oxygen consumption rates and water flow requirements of pacific salmon (oncorhynchus spp.) in the...

.4quaculture, 109 (1993) 281-313 Elsevier Science Publishers B.V.. Amsterdam

281

AQUA 40026

Oxygen consumption rates and water flow requirements of Pacific salmon (Oncorhynchus

spp.) in the fish culture environment*

William E. McLean”, Jorgen O.T. Jensenb and Donald F. Alderdiceb,’ aDepartment ofFisheries and Oceans, Enhancement Operations Branch, Quinsam Salmon Hatchery.

Campbell River, B.C., Canada bDepartment of Fisheries and Oceans, Pacific BiologicalStation, Nanaimo. B.C.. Canada

(Accepted 9 July 1992)

ABSTRACT

McLean, W.E., Jensen, J.O.T. and Alderdice, D.F., 1993. Oxygen consumption rates and water flow requirements of Pacific salmon (Oncorhynchus spp.) in the fish culture environment. Aquaculture, 109: 281-313.

In salmon culture facilities, the balance between oxygen consumption and supply is critical and so a model to predict oxygen levels in rearing facilities has been constructed. The oxygen concentration at the outflow of a rearing pond ( Cf) was expressed as a function of oxygen concentration of the inflow stream (C,), loading rate (Lr=biomass of fish per unit water flow), reaeration rate within the pond (k) and oxygen consumption of the fish (Ro). Of these variables, Ro is the most complex and difficult to model.

To model Ro, oxygen consumption rates for both juvenile and adult salmon were measured under typical fish culture conditions. Average daily Ro values for juveniles had a mean of 245.5 mg kg-’ h-’ (s.d.=67.4, n= 129) and ranged between 83 mg kg-’ h-’ for starved fish, to over 400 mg kg-’ hh’ for fed fish. Peak daily Ro values often were 20% higher than average daily values (mean peak- to-average ratio= 1.2048, s.d. = 0.075, n = 79). Ro values for nonfeeding adult salmon varied between 35 mg kg-’ h-’ for fish holding quietly in low velocity ponds to over 300 mg kg-’ h-’ for actively migrating and spawning adults.

Measured Ro values for juveniles were related to ration level, temperature and fish weight using a variety of empirical models. It was found that the product of ration and temperature accounted for 65% of the variation in measured values. The most accurate predictor of Ro was the Response Surface Analysis (RSA) model of Schnute and McKinnell ( 1984).

The maximum allowable load rate, or carrying capacity of the water supply, occurs when C, is at the lowest acceptable level. These limits to Lr define the water flow requirements forjuvenile rearing.

Correspondence to: William McLean, Department of Fisheries and Oceans, Enhancement Op- erations Branch, Quinsam Salmon Hatchery, Box 467, Campbell River, B.C., Canada V9W 5Cl. *Dedicated to Dr. J.R. (Roly) Brett, who passed away 4 February 1991 at Nanaimo, B.C., Canada. ‘Present address: Biological and Environmental Consultant, 63 12 Icarus Drive, Nanaimo, B.C., Canada V9V 1 B5.

0044-8486/93/$06.00 0 1993 Elsevier Science Publishers B.V. All rights reserved.

282 W.E. MCLEAN ET AL.

Using oxygen criteria of Davis ( 1975) to define acceptable oxygen levels and Ro values predicted from the RSA model, carrying capacity under a variety of conditions was calculated. The limitations of this model also are discussed; it is recognized that other water quality factors or disease considera- tions may further limit the carrying capacity of a water supply.

INTRODUCTION

Salmon consume oxygen and excrete detrimental waste products such as ammonia, carbon dioxide and suspended solids. This must be accounted for in the design and operation of salmon culture facilities if environmental quality is to be maintained. The simplest way to satisfy the demand for oxygen and prevent the accumulation of ammonia and suspended solids is to provide the fish culture facility with a large inflow of aerated water of high quality. A high inflow rate supplies oxygen and flushes away waste products so that the pond environment satisfies the requirements for fish health and growth.

In single use facilities, where water passes through the pond once, oxygen depletion rather than waste product accumulation is usually the factor that limits the number of fish (Colt and Orwicz, 199 1). In reuse ponds where the water is aerated and recycled, the accumulation of waste products can be detrimental and limit production. However, oxygen reduction generally is the first limiting factor and therefore is of prime concern in fish culture operations.

The pond outflow oxygen concentration is measured routinely in fish culture facilities as a way of monitoring environmental quality. Detection of low oxygen levels at the pond outflow requires an increase in water flow rate or a decrease in fish biomass.

The oxygen concentration in an idealized pond is a function of the oxygen inflow, the number of fish in the container and their rate of oxygen consumption (Ro). Of these, the oxygen consumption rate is the most variable and difficult to predict. A realistic model for Ro would not only assist fish culturists in predicting water flow requirements, but would also provide insight into how oxygen concentration varies under different conditions.

This report presents a framework for predicting the pond oxygen level and its carrying capacity and also discusses the problems associated with devel- oping a general oxygen consumption rate model. Furthermore, Ro values measured for feeding juvenile fish in large-scale rearing ponds are presented. Some oxygen consumption rates for non-feeding adult fish in holding ponds and spawning channels also are included.

The collected data involve a limited range of temperature and ration levels, from which both empirical and semi-empirical predictive models are developed for juvenile salmon. These models relate Ro to fish weight, temperature and ration level. Also, a theoretical predictive model is built from basic knowledge governing how these variables influence metabolism. The accu- racy and limitations of the predictive models are compared.

OXYGEN CONSUMPTION OF PACIFIC SALMON AND WATER FLOW 283

The oxygen consumption rates examined in this paper were attained largely in salmon enhancement facilities of the Department of Fisheries and Oceans, Canada, located on Vancouver Island, British Columbia. These include the Conuma, Nitinat, Puntledge, Big Qualicum and Quinsam (hatchery and juvenile culture) facilities, and the Big Qualicum and Little Qualicum spawning channels. In these facilities the species under culture are predominately Pacific salmon (Oncorhynchus). Data are presented for the following species: 0. nerka - sockeye; 0. kisutch - coho; 0. tshawytscha - chinook; 0. keta - chum.

FRAMEWORK FOR A GENERAL OXYGEN MODEL

The oxygen consumption rate (Ro) is defined as oxygen consumed in mil- ligrams per kg of fish (wet weight ) per hour (mg kg- ’ h- ’ ) . This value can be calculated by measuring the oxygen concentration at the pond outflow ( C,) . Ro is related to the change in oxygen concentration through the pond ( C, - C,), the water flow rate (Q) and the total biomass of fish in the pond (B) where

Ro=((C,- Cr) Q60)lB (1)

and Ro = oxygen consumption rate (mg kg- ’ h- ’ ), C, = oxygen concentration at pond inflow (mg l- ’ ), Cp oxygen concentration at pond outflow (mg l- ’ ) , Q= water flow (1 min- ’ ) and B= total biomass of fish in the pond (kg).

Oxygen consumption values based on a few grab samples taken over a day are difficult to interpret. The values simply may reflect a momentary disturbance among the cultured fish and may not be representative of the pond under normal conditions. Hence Ro data based on sporadic grab samples are highly variable and difficult to model. Continuous oxygen monitoring, in general use in this study, overcomes most of these difficulties. Ro values can be calculated using equation 1 at any time to reveal daily patterns of oxygen consumption. Hence, more meaningful peak and average daily Ro values can be calculated.

The Ro value approximates the respiration rate of the fish. However, since Ro is calculated from oxygen depletion over the whole pond (C, - C,), its estimate will be influenced by reaeration within the pond, photosynthesis of algae and by the oxidation of pond wastes. In most single pass production rearing units these effects will be small compared to fish respiration. Hence, for rearing ponds monitored in this study, it has been assumed that the Ro value is a reasonable approximation of the metabolic rate.

Equation 1 can be made into a predictive model for oxygen concentration at the pond outflow by solving for C’ that is,

Cf= Ci - (Ro B/60 Q) = Ci - (Ro b/60) (2)


Load rate Lr is the ratio of fish biomass B (kg) to water flow rate Q (1 min- ’ ), Lr=B/Q.

Equation 2 applies to both circulating (mixed flow) and raceway (plug flow) type ponds when steady state conditions prevail (i.e. when Ci and Ro are constant over time). In an ideal raceway the flow of fluid through the vessel is orderly with no element of fluid mixing with any other element. The oxygen concentration decreases down the length of the raceway from Ci at the inflow to C’at the outflow. In circulating ponds the inflow water is uniformly mixed almost immediately; the oxygen concentration is the same throughout the pond and there is no gradient. In this case the oxygen concentration throughout the pond is given by the outflow oxygen C,

If Ro or Ci change, C’also changes to reflect the new conditions. However, the change in C’is not instantaneous and is affected by the volume Vand flow Q through the rearing container (Steffensen, 1989). In an idealized rearing vessel the time lag in C’is a function of the mean residence time, V/Q.

The lag in C’can be derived from the mass balance for oxygen. The change in the mass of oxygen in a pond during a small time increment Dt is given by: Change = O2 flowing in - O2 flowing out - O2 consumed by fish In time increment Dt, the change in mass DM is:

DM=Ci Q Dt-CfQ Dt- (RO B/60)Dt (3)

Dividing both sides of this equation by VDt and taking the time increment to the limit dt (i.e. converting to a differential equation) gives:

dc ,dt,c’ Q-ROBl6O-CfQ f V

Note. DM/ V-change in mass/volume ’ Dt change in time

= dC/dt in limiting case.

Equation 4 is a first order linear differential equation which can be solved analytically using the method of integrating factors. If the oxygen consumption rate has been steady at Ro and suddenly increases to Ro’ at time t=O, then the oxygen concentration at the pond outflow C,is given by:

Cf=Ci-RoLr/60+ (Ro’ito) Lr (exp(-Qt/V) - 1)

At t= 0, Cf is given by Ci-RO Lr/60 and as t increases, C’approaches the new steady state level Ci- Ro’ Lr/60. The rate at which C, approaches this new level depends on the mean residence time of the rearing container. Fig. 1 shows how C-approaches the new level at different residence times if the oxygen consumption rate suddenly increases from Ro= 150 to Ro’ = 300 mg kg- ’ h- ’ at mid-day ( 12 h) . Values were calculated for ponds with mean residence


10

I I I I I I 1 1 I I I t lo 0 2 4 6 8 10 12 14 16 16 20 22 24

Time (hours)

Fig. 1. Simulation of pond outflow oxygen concentration C, when the metabolic rate suddenly increases from 150 (Ro) to 300 (Ro’ ) mg kg- ’ h- ’ at midday. Outflow oxygen was calculated for ponds with mean residence times (MRT) of 30,60 and 120 min, Lr of 0.6 kg I-’ min and C, of 11 mg I-‘. Ro values calculated from C,are also shown.

times ( V/Q) of 30,60 and 120 min, a load rate Lr of 0.6 kg I- ’ min and C, of 11 mgl-‘. Ro values calculated from C, (using equation 1) will be in error during this

transition to a new steady state. Calculated Ro values are shown in Fig. 1. For a mean residence time of 30 mitt, the calculated Ro finally approaches the actual Ro of 300 mg kg-’ h- ’ 2 h after Ro was altered.

In production rearing ponds where Ro varies in complex ways over the day, equation 4 can be solved numerically for C’using the Runge-Kutta method (Spain, 1982). To quantify the error in the calculated Ro value, simulation trials were performed for ponds with different mean residence times. In these trials the actual Ro has been changed every 6 min to reflect the rapid changes in fish activity that occur in rearing ponds. To simulate a typical daily pattern, Ro reached a maximum in the afternoon. Ro calculated from C’would be expected to follow the actual Ro values if the mean residence time was short. Fig. 2 shows calculated values and actual values for ponds with residence times of 30 and 120 min. The calculated values lag behind the actual values slightly and also fail to show the complex variation in Ro. However, even with a mean residence time of 120 min, the calculated Ro values can be used to give an accurate estimate of the average daily Ro value. In this example the average daily Ro was 248.9 mg kg- ’ h- ’ while the average calculated value was 249.1 mg kg-’ h-‘. This difference represents the error in average daily values when Cfand equation 1 are used to calculate Ro.

Simulation runs were performed for mean residence times between 30 and


400

_- ,

; 7 300

cn Y

F 200

cz

100

I / * Calc. Ro MRT 12d I

I I I

01 1 ’ 1 1 1 1 ’ 1 1 1 I 0 2 4 6 '3 10 12 14 16 18 20 22 24

Time (hours)

Fig. 2. Simulation showing differences between actual and calculated Ro values for ponds with residence times of 30 and 120 min. Actual Ro values vary frequently (every 6 min) over the day while Ro values calculated from C,fail to track the actual Ro unless MRT is short.

600 min. For mean residence times less than 90 min the error in average daily values is negligible. Since the mean residence times of juvenile rearing ponds examined in this paper were short, the simple steady state model (equations 1 and 2) has been used to model oxygen. However, for ponds with long residence times, the full implications of equation 4 must be taken into account in the development of a predictive model.

If the minimum acceptable oxygen concentration at the outflow (C’) is specified, equation 2 can be used to predict the maximum allowable load rate (Lr) or carrying capacity of the water supply

Lr= 60 ( C; - Cr) /Ro. (6)

In long shallow spawning channels, reaeration can be significant. The Stree- ter Phelps equation (Clark et al., 197 1) describes how oxygen concentration varies when water is simultaneously deoxygenated and reaerated. This equation was used by McLean ( 1979) to predict the combined effects of fish respiration and reaeration. The oxygen concentration at the outflow of the channel ( Cr) is

c’=cs-gf (l-exp(-k~/Q))-(C,-C;) exp(-kV/Q) (7)

where C,= saturation oxygen concentration (mg l- ’ ), V= volume of container (1) , k= reaeration coefficient (min- ’ ) , exp (x) = e” and Lr, Q, C,, C’ and Ro are defined in equations 1 and 2.

Equation 7 can be solved for Ro:


R. = vk60 [(Cs-Cf)-(Cs-Ci) expG-k VQ)l LrQ [l-ewGWQ)l

Thus, measuring oxygen depletion over the length of the channel ( C,- CJ), and knowing the reaeration coefftcient (k), allows calculation of the oxygen consumption rate of the fish (Ro).

The coefficient (k) was calculated from an empirical relationship for reaeration within streams (Gromiec, 1989):

kzO = C @.969/~‘.673 (9)

where k,,=reaeration coefficient at a temperature of 20°C (min- ’ ),

C=constant (0.0015 1250), U=average stream velocity (m min-’ ) and H= average stream depth (m ). The value of k at any temperature t is related to kzO by the following formula (Gromiec, 1989)

k=kzO 1.024’r-20’ (10)

MATERIALS AND METHODS

Rearing ofjuvenile salmon

Rearing pond description. At Puntledge Hatchery, approximately 1 million chum salmon fry were reared in a rectangular concrete raceway. This rearing unit (4.56 x 16.75 m) was operated at a water depth of 0.95 m. A V-notch weir at the pond inflow measured water flows. The average flow over the study period was 2300 1 min-‘.

Chum fry at Conuma Hatchery were also reared in a rectangular concrete pond. This pond, 7.0 x 26.5 x 1 m deep, held approximately 2.5 million fry (Sucwoa River stock). Water was introduced via a diffuser at the head of the pond and also by means of an inclined chute. The chute purposely was set off centre so that a circulating motion was established around the pond. This tended to concentrate solid waste in the centre of the pond and increase cleaning efficiency. Water flows were measured using a broad crested weir at the pond outflow. Average flow was 2500 1 min- ‘.

Coho at Quinsam and Puntledge Hatcheries were reared in Burrows circulating ponds (Burrows and Chenoweth, 1970). The ponds at Quinsam each contained approximately 100 000 fish while the Puntledge pond contained 225 000 coho at the time of oxygen monitoring. These ponds were 22.86 x 5.18 m, and operated at a water depth of 0.9 1 m. Water flows, measured using a V-notch weir at the pond outflow, varied between 2300 and 2700 1 min-’ when oxygen measurements were made.

Chinook fingerlings were reared in concrete raceways at Nitinat Hatchery. One intensively monitored pond contained approximately 600 000 fish; it was


3 1.7 x 4.5 m with a maximum operating depth of 1.69 m. Water flow was measured using a 90” V-notch weir at the pond outflow. Average water flow over the rearing period was 3740 1 min- ‘.

Fish culture procedures and parameters. Study ponds were treated as typical production rearing units. Normal fish culture operations such as cleaning, sampling and removal of dead fish were performed routinely. In all cases fish were fed Oregon Moist Pellet (OMP ). At Conuma, hand feeding was carried out during the daylight hours; at other facilities hand feeding occurred in con- junction with use of automatic feeders. Feed rates were calculated in grams of dry food per 100 g of fish (wet weight ) per day (or % dry food per day). Dry food input was calculated by taking 70% of the total daily ration fed; that is, it was assumed that OMP had a moisture content of 30%.

Pond biomass was estimated from a knowledge of the pond population and average fish weight. The population at a particular time was estimated by subtracting the daily count of dead fish from the number initially ponded. Average weight was calculated from length/weight samples taken every 2 weeks.

These samples were used to construct simple growth models so that the average weight of fish on non-sample days could be estimated. It was assumed that fish grow in short exponential bursts (Brett, 1979).

At Quinsam, Nitinat and Puntledge Hatcheries, average daily water temperature was calculated from the hatchery thermograph records. At Conuma, average daily temperature was calculated from spot checks made in the morn- ing and afternoon.

Oxygen monitoring. Daily oxygen concentration profiles were measured for juvenile fish at Conuma, Puntledge, Quinsam and Nitinat Hatcheries. Oxy- gen concentration at the pond outflow was monitored continuously and consumption rates were calculated at l-h intervals over 24 h. The resulting data for a single day consisted of 24 equally spaced rate measurements, and the mean daily oxygen consumption rate was calculated by simply averaging these 24 values. At Nitinat the oxygen profile was more intensively monitored. Ox- ygen readings were taken at the inflow and outflow of the pond every IO min over the day so that average daily oxygen consumption rates were calculated from 144 individual values.

Oxygen consumption rates of adult salmon were measured at Big Qualicum Hatchery and at the Little Qualicum spawning channel. These fish were near- ing maturity and were not feeding. Monitoring was performed over a range of fish culture operations such as crowding and sorting, producing activity levels in the adults typical of those found in the fish culture environment.

Oxygen was monitored continuously using a variety of oxygen meters: Or- bisphere model 2603 (Puntledge chum); Leeds and Northrup model 7931


(Puntledge coho); Yellow Springs Instruments model 57 (Quinsam coho and Conuma chum); Leeds and Northrup model 7932 (adult chum and chinook) ; and Oxyguard model 4 (Nitinat chinook). Data were recorded either on Houston Instruments or Leeds and Northrup chart recorders. At Nitinat an electronic data acquisition system was used to send the oxygen signal directly to a personal computer.

Meters were calibrated using the Winkler titration method for the deter- mination of dissolved oxygen (A.P.H.A., 1980). The Winkler test also was used to measure the oxygen concentration of the inflow water. Oxygen concentration data, along with those for biomass and water flow, were used to calculate the average daily oxygen consumption rate Ro (equation 1).

Laboratory measurements. Oxygen consumption rates of feeding sockeye salmon were measured at the Pacific Biological Station, Nanaimo, B.C. using methods fully described by Brett ( 1976). These measurements, made on small groups of fish under controlled conditions, involved a wide range of ration levels and water temperatures.

The fish were fed OMP and the ration level originally was reported in “grams of dry food per 100 g of dry fish per day”. To convert these ration levels to the more common hatchery unit of percentage dry food per day (grams of dry food per 100 g of fish flesh per day), the fish were assumed to have a moisture content of 75%. Therefore a ration level of 4 g dry food per 100 g dry fish per day would be equivalent to 1 g dry food per 100 g wet weight of fish per day (% day- ’ ) . This assumption was reinforced by 2 10 measurements made on Quinsam coho ( 17 to 37 g); mean moisture content = 75.5%, s.d. = 1.55.

Adult holding and spawning

Little Qualicum spawning channel. This channel, 4 170 x 6.1 m, has an average water depth of 0.4 m. Water flowing into the channel is measured by a calibrated gauge at the inflow. Typically, the channel operates at 76.5 m3 min- ’

(45 cfs). Adult salmon are counted into the facility and the dead are removed daily to obtain an estimate of the number and size of live fish in the channel.

Oxygen consumption rates were calculated from continuous oxygen monitoring at the channel outflow. Container residence time was not taken into account. However, the effect of reaeration was included in the calculation of Ro (equations 8 to 10).

Big Qualicum adult holding facilities. The holding ponds are constructed of concrete and are 82 x 4.9 m and 1.3 m deep. Water flow rates were measured using a rectangular weir at the pond outflow. Oxygen consumption rates were measured under normal conditions when the fish were at rest and also during


crowding operations. At that time, fish culturists would push a screen down the length of the pond to force fish into a mechanical lift.

RESULTS

Oxygen consumption rate data were collected along with temperature, fish size and daily ration at five locations. Data are summarized for different species and locations in Table 1.

Juvenile salmon

Puntledge Hatchery chum. Average daily oxygen consumption rates (Ro) for chum fry were calculated from equation 1 (Table 1 entries 1- 17). Mortality over the rearing period was low - less than 0.5% loss occurred between com- pletion of ponding on 25 April and release on 29 May (34 days).

Length/weight samples provided a relationship between mean weight and time. Between the initial sample on 16 April (day 0) and release on 29 May (day 43), mean weight was predicted by W~O.376 exp (0.0324 T), where IV’, mean weight (g ), T= time (no. of days from 16 April). This relation (r=0.998) yielded a specific growth rate of 3.24% day-’ and predicted a final weight at release on 29 May of 1.5 1 g.

Oxygen concentration of the inflow water varied between 10.9 and 12.0 mg 1-l over the study period. These levels were consistently near saturation (mean = 100.02%, s.d. = 0.90, n = 18 ) and hence changes in oxygen concentration simply reflected changes in water temperature.

Outflow concentrations generally were 2 to 5 mg l- ’ lower than the inflow levels. The lowest oxygen concentration measured was 6.8 mg 1-l; this occurred at 16.00 h on 28 May.

Water flows were reasonably constant, varying between 2200 and 2400 1 min-‘. Hence the pond load rate, Lr (kg l- ’ min) increased steadily as the fish grew and pond biomass increased. The highest load rate noted during the study was 0.6 kg 1-r min. Fish density in the pond at that time was 19.8 kg rnm3.

Conuma Hatchery chum. Eighteen measurements of average daily oxygen consumption rate were made on chum salmon (Sucwoa River stock) at Con- uma Hatchery between 12 March and 12 April (Table 1, entries 18-35 ).

Sucwoa River chum fry were ponded on 24 February 198 1 and released to their river of origin on 13 April 198 1. Oxygen monitoring began on 10 March and was carried on until release. During this period, overall accountable mortality was 1.34%. As described earlier, the 7-m-wide pond at Conuma did not have the characteristic flow pattern of a raceway. Instead there was a circulating motion around the perimeter of the pond. This flow pattern was modified


and the pond was converted back to a conventional raceway on 28 March. Hence the rearing environment was characterized by higher water velocities between 24 February and 28 March and lower velocities between 28 March and release.

Accordingly, two separate models were used to quantify growth of Conuma chum. Between 24 February and 28 March growth was described by I++ 0.504 exp(0.0159 T), and between 28 March and 13 April by W~O.840 exp(0.0309 T). Thus the specific growth rate over the high velocity period was 1.59% day-’ while the rate of growth over the low velocity period was 3.09% day-‘.

Oxygen concentration of the inflow stream was measured nine times during the study. Levels were very near saturation (mean = 97.4%, s.d. = 1.13) and varied between 11.7 and 12.5 mg 1-l. Outflow concentration dropped to a minimum of 6.2 mg 1-l at 18.00 h on 9 April. As the fish grew and the biomass increased, the load rate increased to a maximum, just prior to release, of1.375kgl-‘min (flow=24321min-‘).Ponddensityatthistimewas 17.5 kg mW3.

Quinsam Hatchery coho. Oxygen consumption rates for Quinsam coho are summarized in Table 1 (entries 36-59). Oxygen concentrations at the inflow of the ponds were between 10.5 and 11.3 mg 1-l while outlet concentrations generally did not drop below 6 mg l- ’ .

Coho were ponded in late February of 1975 at an average weight of 0.35 g and released as smolts over the spring of 1976 (410 days later) at approximately 30 g. Growth occurred in two distinct phases. Over the first 175 days fish grew with a specific growth rate of 2.0% day-‘; over the last 200 days of rearing, growth decreased to 0.47% day-‘. Over the entire rearing period there was an accountable mortality of 10%.

Puntledge Hatchery coho. Oxygen consumption rates for Puntledge coho are summarized in Table 1 (entries 60-63 ) . Outflow oxygen concentrations were above 6 mg l- ’ while inflow levels were between 9.5 and 10 mg l- ’ .

The group of coho under study at Puntledge experienced a severe outbreak of furunculosis just prior to the period of oxygen monitoring. Mortality rate peaked on 4 July at 3.2% day-‘. By the time oxygen testing began on 9 July the rate had dropped to 0.3% day-‘. Over this period the specific growth rate was only 0.76% day-‘.

Pacific Biological Station sockeye. As described earlier, oxygen consumption rates of feeding sockeye fingerlings (Brett, 1976 ) were measured on fish held under laboratory conditions at the Pacific Biological Station in Nanaimo. These involved a wide range of ration levels and water temperatures. This information is presented for comparison with the production scale hatchery data (Table 1, entries 64-9 1).


TABLE 1

Average daily oxygen consumption rates (Ro mg kg-’ h-l), temperature (“C), fish weight (g) and ration level (% dry food day-‘) for four species of juvenile Pacific salmon examined at five sites. Descriptive statistics for these parameters are given following presentation of each data set

No. Date Weight

(9)

Temp.

(“Cl

Ration (Oh day-‘)

Ro (mg kg-’ h-‘)

Puntledge Hatchery chum fry-l 980 I 12 May 0.873 2 13May 0.902 3 14 May 0.932 4 15 May 0.962 5 16 May 0.994 6 17 May 1.027 7 18 May 1.061 8 19 May 1.096 9 20 May 1.132

10 21 May 1.169 11 22 May 1.208 12 23 May 1.247 13 24 May 1.288 14 25 May 1.331 15 26 May 1.375 16 27 May 1.420 17 28 May 1.467

Mean 1.146 s.d. 0.187 Minimum 0.873 Maximum 1.467

Conuma Hatchery chum fry-l 98 1 18 12 Mar 0.651 19 13 Mar 0.661 20 14 Mar 0.672 21 21 Mar 0.751 22 22 Mar 0.763 23 23 Mar 0.775 24 26 Mar 0.813 25 31 Mar 0.92 1 26 I Apr 0.950 27 2 Apr 0.980 28 3 Apr 1.01 29 4 Apr 1.04 30 7 Apr 1.14 31 8 Apr 1.17 32 9 Apr 1.21 33 10 Apr 1.25 34 1 I Apr 1.29 35 12Apr 1.33


9.25 2.550 316.0 9.75 2.469 310.9 9.75 2.389 329.8 9.75 2.315 309.3

10.00 2.241 323.2 10.50 2.169 314.5 10.80 2.100 348.8 10.00 2.033 345.9 10.50 3.102 321.5 10.50 3.004 305.9 10.00 2.907 259.0 10.50 2.817 201.9 10.50 2.727 259.0 11.10 2.639 283.8 10.60 2.555 324.0 11.10 2.474 350.2 11.00 2.395 367.4 10.33 2.523 310.1 0.53 0.313 40.5 9.25 2.033 201.9

11.10 3.102 367.4

6.9 1.226 212.3 6.5 1.207 221.0 6.5 1.188 251.5 6.4 1.803 220.6 6.1 1.776 225.8 6.1 1.767 235.4 6.9 1.689 255.4 5.8 1.495 290.7 5.6 1.755 275.0 5.9 1.703 261.2 5.7 1.651 237.0 5.7 1.602 230.1 5.8 1.462 205.6 5.7 1.417 216.4 5.5 1.543 223.0 5.8 1.497 211.4 5.6 1.451 201.8 6.2 1.407 173.6 6.04 1.535 230.4 0.439 0.199 28.2 5.5 1.188 173.6 6.9 1.803 290.7


No. Date Weight

(9)

Temp.

(“C) Ration (% day-‘)


Quinsam Hatchery coho juveniles-1975/76 36 13 Sept 1975 12.0 37 I7 Sept 12.6 38 18 Sept 12.8 39 23 Sept 13.2 40 24 Sept 13.2 41 6 Feb 1976 21.9 42 7 Feb 22.1 43 12Feb 22.8 44 13Feb 23.0 45 16Feb 23.4 46 26 Feb 24.9 47 2 Mar 25.0 48 5 Mar 24.6 49 I I Mar 25.3 50 4 Apr 30.3 51 8 Apr 30.8 52 9 Apr 30.9 53 13Apr 31.3 54 15Apr 31.7 55 16 Apr 31.8 56 17Apr 31.9 57 22 Apr 32.5 58 28 Apr 33.2 59 29 Apr 33.3


Puntledge Hatchery coho juveniles-l 98 1 60 9 July 4.65 61 13 July 4.92 62 14 July 4.99 63 15 July 5.06


10.2 1.616 214.9 10.0 1.688 262.4 9.9 1.781 276.4

10.0 1.711 227.3 10.0 1.711 242.6 8.6 1.023 182.7 8.8 1.017 202.1 8.4 0.991 219.4 8.4 0.988 215.3 8.8 1.013 208.9 8.3 1.120 207.7 8.3 0.747 157.6 8.9 1.417 284.9 9.0 1.361 218.7 9.9 0.921 251.3 9.8 0.904 192.0

10.0 0.903 216.1 9.6 0.890 241.0 9.5 0.884 197.0 9.7 0.880 196.9

10.0 0.877 199.3 9.7 0.862 226.6

10.0 0.844 238.3 10.0 0.842 238.6 9.41 1.125 221.6 0.67 0.338 29.5 8.3 0.747 157.6

10.2 1.781 284.9

15.4 1.85 464 16.4 1.64 359 16.6 1.62 420 17.2 1.60 443 16.4 1.68 422 0.748 0.116 45.4

15.4 1.60 359 17.2 1.85 464

Pacific Biological Station sockeye (Brett, 1976) 64 3.45 20.0 65 5.15 20.0 66 7.10 20.0 67 11.25 20.0 68 17.80 20.0 69 9.51 15.0 70 11.60 15.0 71 14.40 15.0 72 18.50 15.0 73 20.10 15.0 74 19.30 15.0 75 10.20 10.0

0.00 132.0 0.38 184.0 0.755 279.0 1.090 265.0 1.413 317.0 0.00 83.9 0.388 146.8 0.713 179.7 0.988 226.9 1.213 224.1 0.975 180.0 0.00 82.7

294

TABLE 1 (continued)

W.E. MCLEAN ET AL.

No. Date Weight

b.s)

Temp. (“C)

Ration (%day-‘)


76 12.70 77 15.20 78 16.90 79 15.70 80 18.30 81 19.60 82 19.60 83 19.20 84 20.80 85 17.80 86 17.90 87 22.20 88 23.60 89 18.30 90 19.60 91 24.30


Nitinat Hatchery chinook juveniles-1990

10.0 0.388 134.8 10.0 0.700 136.2 10.0 0.963 151.0 10.0 1.125 188.3 5.0 0.250 138.8 5.0 0.750 119.6

10.0 0.375 126.1 10.0 0.625 153.2 10.0 1.000 187.6 15.0 0.500 179.9 15.0 0.875 230.6 15.0 1.125 291.3 15.0 1.500 310.2 20.0 0.875 233.4 20.0 1.250 299.1 20.0 1.625 416.7 14.29 0.78 198.0 4.66 0.448 79.4 5.0 0.00 82.7

20.0 1.625 416.7

92 1 Apr 1.90 6.30 1.43 203.48 93 2 Apr 1.94 6.30 1.03 196.51 94 3 Apr 1.98 6.40 1.73 185.85 95 4 Apr 2.02 6.50 1.34 200.22 96 6 Apr 2.10 6.60 1.36 210.74 97 7 Apr 2.15 6.70 1.34 222.24 98 8 Apr 2.19 6.70 1.30 217.37 99 9 Apr 2.24 6.80 1.71 212.61

100 10Apr 2.28 6.80 1.19 2i 1.29 101 11 Apr 2.33 6.80 1.76 241.48 102 l2Apr 2.38 6.80 1.70 237.16 103 13Apr 2.43 6.90 1.49 219.15 104 14Apr 2.48 6.90 1.46 209.39 105 15 Apr 2.53 6.90 1.43 207.94 106 16Apr 2.58 7.00 1.69 211.84 107 17Apr 2.63 7.00 2.06 232.44 108 18Apr 2.69 7.00 1.51 237.83 109 19Apr 2.74 7.10 1.48 237.95 110 20 Apr 2.80 7.10 1.45 255.77 111 21 Apr 2.86 7.20 1.42 259.47 112 22 Apr 2.92 7.20 1.39 273.28 113 23 Apr 2.98 7.20 1.37 291.61 114 25 Apr 3.10 7.30 1.75 271.90 115 26 Apr 3.17 7.30 1.71 279.08 116 27 Apr 3.23 7.30 1.68 301.38 117 28 Apr 3.30 7.40 1.64 330.36 118 29 Apr 3.37 7.40 1.61 309.99 119 2 May 3.58 7.40 1.51 268.81 120 4 May 3.73 9.25 1.70 316.72 121 5 May 3.81 11.30 2.85 384.45


No.

122 123 124 125 126 127 128 129 130

Date

8 May 9 May

11 May 12May 13 May 14May 15 May 16May 17May Mean s.d. Minimum Maximum

Weight Temp. Ration Ro

(g) (“C) (% day-‘) (mg kg-’ h-‘)

4.05 9.10 1.68 304.27 4.13 10.10 1.97 312.27 4.30 11.30 1.89 235.94 4.39 9.80 1.85 211.33 4.48 9.50 1.82 245.65 4.58 9.90 1.78 267.57 4.67 10.50 1.74 270.47 4.77 10.20 1.71 274.74 4.86 10.70 1.67 290.35 3.09 7.84 1.62 252.59 0.91 1.54 0.30 44.46 1.90 4.3 1.03 185.85 4.86 11.3 2.85 384.45

TABLE 2

Oxygen consumption rates for adult chum salmon at the Little Qualicum spawning channel. Gross Ro (equation I), Ro value corrected for reaeration (equation 8) and associated load rates are given, Sample types: G, grab; DA, daily average; P, daily peak Ro; M, daily minimum Ro

Date Sample type Temp. DO Load rate Gross Ro and time (“C) (mg I-‘) (kg I-’ min) (mg kg-’ h-t) Tzg kg-’ h-l)

18 Nov 1986 G, 19Nov 1986 G, 19 Nov 1986 G, 20 Nov 1986 G, 21 Nov 1986 G, l2Nov 1987 DA I2 Nov 1987 P, 13 Nov 1987 DA 13Nov 1987 M 13 Nov 1987 P, 14 Nov 1987 DA 14 Nov 1987 P. IS Nov 1987 DA 15 Nov 1987 P. 23 Nov 1987 G, 24 Nov 1987 G, 25 Nov 1987 G. 27 Nov 1987 G.

1 Dee 1987 G, 2 Dee 1987 G,

16.30 17.00 19.00 17.00 17.00

20.00

23.00

01.00

22.00 13.15 16.30 15.30 13.20 15.35 16.15

9.3 5.5 2.17 1163 194 7.1 3.4 2.113 225 262 7.5 4.8 1.65 241 271 8.0 4.9 I .44 271 301 8.8 5.6 1.40 219 244 9.9 6.2 1.01 265 313

5.9 1.01 288 340 9.4 5.7 1.13 268 317

6.1 1.13 245 290 5.1 1.13 296 351

8.6 5.9 1.24 232 273 5.6 1.24 247 291

8.7 5.9 1.19 243 286 5.6 1.19 259 305

9.2 7.5 0.99 193 226 8.7 5.8 1.21 247 284 9.2 6.2 0.90 324 366 9.3 7.5 0.94 233 267 7.8 8.6 0.67 200 225 8.1 9.0 0.5 1 230 260


TABLE 3

Oxygen consumption rates (equation 1) for adult chinook salmon at Big Qualicum holding ponds and associated load rates. Sample types: P, daily peak Ro; Da, daily average

Date Sample type Temp. DO Load rate and time (“C) (mgl-‘) (kgl-‘mitt)

Ro (mgkgg’h-‘)

12 Ott 1987 P, 20.00 9.0 4.8 1.84 221 13 Ott 1987 DA 8.7 9.4 1.84 69 13 Ott 1987 P, 00.00 7.7 1.84 122 14 Ott 1987 DA 9.2 9.4 1.84 65 14Oct 1987 P, 09.15 5.5 3.12 113 15 Ott 1987 DA 9.0 10.1 1.84 45 15 Ott 1987 P, 17.00 9.1 1.84 79 16 Ott 1987 DA 10.0 10.3 1.93 39 16Oct 1987 P, 17.00 9.2 1.93 70 17Oct 1987 DA 10.0 10.4 1.93 35 17 Ott 1987 P. 18.00 9.8 1.93 54 18 Ott 1987 DA 10.0 10.3 1.93 36 18 Ott 1987 P. 19.00 9.5 1.93 61

Nitinat Hatchery chinook. Average daily oxygen consumption rates are summarized in Table 1 (entries 92-l 30). .The oxygen concentration of the inflow water ranged between 10.3 and 11.8 mg 1-l (near 100% of saturation) while the lowest outflow concentration recorded was 6.6 mg l- ‘.

Oxygen consumption of chinook fingerlings was monitored continuously between 3 1 March 1990 and 18 May 1990 when resulting smolts were released to the ocean. Accountable mortality was less than 0.5% over the entire rearing period. Average fish weight ( W’) increased with time (T days) whereby W~0.56exp(0.02045 T); ~0.9990, n= 15. Average specific growth rate over the rearing period was 2.045% day- ‘.

Peak vs average daily oxygen consumption rates forjuvenile salmon. A number of daily oxygen profiles were examined to estimate the relationship between peak and average daily oxygen consumption rates. The peak rate was defined as the average rate over the most active 2-h period of the day (24-h period). This usually occurred in mid to late afternoon. The ratios of the peak daily to average daily oxygen consumption rates varied between 1.03 and 1.44 with a mean of 1.2048 (n=73, s.d.=0.075).

Adult salmon Oxygen concentrations at the outlet of both the adult holding facilities at

Big Qualicum (BQ) and the spawning channel at Little Qualicum (LQ) dropped below 6 mg 1-l during periods of peak activity. The lowest measured concentration ( 3.4 mg l- ’ ) occurred at the Little Qualicum on 19 November


1986. Inflow concentration at these sites was near saturation (above 10.5 mg 1-l). In the holding pond at BQ, oxygen depletion was related to fish culture activities such as crowding and sorting; in the spawning channel, oxygen min- ima coincided with aggressive upstream movement and intense spawning activity. Hence the lowest oxygen levels tended to occur at night. Oxygen consumption rates were obtained for chum salmon at the LQ spawning channel (Table 2) and for chinook at the BQ holding facility (Table 3). These data are based both on grab samples taken at specilic times and on average daily values. The oxygen concentration at the pond outflow and the load rate are also shown. Average fish weights of 4.5 and 10 kg respectively were used to calculate the biomass of chum at LQ and chinook at BQ.

OXYGEN CONSUMPTION RATE MODELS

Physiological relationships The effects of temperature, swimming speed, lish weight and ration level

on metabolic rate have been investigated for sockeye (Brett, 1964, 1965, 1976; Brett and Glass, 1973 ) . These studies were directed at answering basic ques- tions about fish physiology, and most of the work was performed in a respi- rometer or in small tanks where experimental conditions could be highly controlled. Nevertheless, many of the insights obtained can be related directly to the problem of oxygen supply in production rearing operations.

A significant finding of this work was the fact that the level of activity affected the relationship between metabolic rate (Ro) and body weight (w). When fish were in a resting state and temperature was constant, Ro decreased as body weight increased. However, as the level of activity increased, the effect of weight decreased until Ro was almost independent of weight at the maximum sustained swimming speed. The relationship is described by: log Ro= log k+ b log w or Ro = k w’, where k= constant, b = weight exponent and w= body weight. The exponent b (slope of log Ro vs log w) increased from -0.12 at standard metabolism to -0.01 at the maximum aerobic activity level. An exponent close to 0 indicates that Ro is almost independent of w (if b=O, Ro=constant).

The relationship between Ro and temperature (t) also was explored. At constant activity, Ro increased exponentially between 0 and 25 ‘C; that is Ro = k exp (ct ). Furthermore, there was a steady increase in Ro as the level of activity increased. However, at maximum sustained swimming speed, the steady increase in Ro with temperature ceased abruptly at 15 ‘C. One expla- nation for this discontinuity lies in the fact that as temperature increases, the oxygen concentration of air-saturated water decreases. Hence, at temperatures above 15 “C, the ambient oxygen concentration may actually limit the active metabolic rate.

The effects of ration level on metabolic rate are complex. Obviously, Ro


increases due to increased swimming activity as fish search for food. How- ever, there is also a substantial increase in oxygen consumption associated with processing of food. Significant increase in metabolic rate occurs following ingestion of a high protein meal. This effect, termed specific dynamic ac- tion (SDA) , is associated with amino acid metabolism ( Priede, 198 5 ) .

Priede proposed a theoretical model for oxygen consumption where total aerobic metabolism is partitioned into three components: standard metabolic rate (Rs) , SDA (Rf) and metabolism due to swimming activity (Ra ) . Then the total oxygen consumption rate Ro= Rs+ Rf+ Ra.

Brett and Glass ( 1973 ) underline the theoretical problems inherent in modelling Ro. It was noted that metabolic rate, as well as being a function of temperature, weight and ration level, was also influenced by many factors difficult to quantify (e.g. excitement, feeding strategy) and could vary rap- idly between wide limits. They also described the limits within which fish must function as lying between the standard and active metabolic rates, defined as the oxygen consumption rates of fish at rest and at their maximum 60-min sustained swimming speed, respectively.

The standard (Rs) and active metabolic rates (Ra) were modelled from data reported by Brett and Glass ( 1973) for sockeye salmon. These measurements were made at temperatures between 5.3 and 20 “C and with fish varying between 1 and 3200 g. Rs and Ra as functions of temperature t ( “C) and weight w (g) were described by the following equations:

Rs~33.175 exp(0.1005 t) w-o.1183 (11)

Ra~316.3 exp(0.0734 t) w--0.0144, t< 15°C (12)

Ra= 1465.3 exp(-0.0288 t) w-0.0053, 15<t<20”C (13)

The metabolic limits and measured average daily Ro values (Fig. 3 ) show that increased activity can cause the metabolic rate to rise by a factor of 10. Note that the active rate as defined earlier refers to the maximum aerobic swimming speed sustainable over a 60-min period. Increased activity would have less influence on the average daily metabolic rate than on the rate measured over a l-h period. Hence average daily values would be somewhat less variable than the limits shown in Fig. 3. Nevertheless, these theoretical limits on metabolism serve to highlight the problem of modelling Ro when swimming speed is unknown.

Predictive models for juveniles The above relationships along with the measured Ro values were used to

develop several predictive models for Ro.

Empirical models. These models are based solely on measured values of Ro (Table 1) . Linear and curvilinear regression equations relating Ro to weight,


Standard Ro

4 6 8 10 12 14 16 18 20 22

Temperature (“C)

Fig. 3. Measured average daily oxygen consumption rates for juvenile salmon ( n = 129, see Table 1 ) as a function of temperature. Ro values (mg kg-’ h-i) are contrasted with the standard and active metabolic rate boundaries calculated from equations 11 and 12.

TABLE 4

Empirical relationships between Roand temperature (t), ration level u) and fish weight (w). A.B,C....T represent constants

Number Model description Form of relationship

I Overall avg Ro value Ro=constant=245.5 mg kg-’ hh’ 2 Simple linear Ro=A+Bf(see Fig. 4)

regression 3 Multiple linear Ro=C+Df+E ~+Fw

regression 4 Multiple curvilinear Ro=I+Jf+Kr+L w+Mf*+N t’+O ~*+Pfl+Q.fw+R wf

regression 5 Stepwise multiple Ro=S+Tji (see Fig. 5)

curvilinear regression

temperature and ration level are shown (Table 4) along with their least squares regression coefficients (Table 5 ). Note that experimental Ro data point number 12 (Table 1) was more than three s.d.s from the multicurvilinear model and was therefore rejected as an outlier. Hence, regression models were derived from the remaining 129 values.

Model 5 is derived using a stepwise procedure where variables that have a very small effect on Ro are cast out of the multiple curvilinear model. The procedure is somewhat arbitrary, but eliminating all variables except ‘f t” (the product of ration level and temperature) results in only a small decrease


TABLE 5

Regression coefficients, standard deviation from regression (s.d. ) *, degrees of freedom (d.f. ) and the multiple R2 for models 1 to 5 in Table 4

Mode1 number

s.d. d.f. R R2 Coefficients

1 67.415 128 2 49.489 127

3 42.445 125

4 31.437 119

5 39.978 127

Not applicable 0.682 0.465 A=136.8916

B=75.1560 0.783 0.613 C= 52.2693

D= 85.6654 E=6.7813 F=0.2749

0.893 0.798 I= 163.4867 J=32.7026 K= -0.4601 L= -1.5529 M= -32.6382 N=0.0343 0=0.2439 P=11.2138 Q= 1.4761 R= -0.2802

0.807 0.65 I S= 146.0663 T= 7.2026

*s.d.* = Sum ( Y,- Y,)2/d.f.; where Yi= measured value and Y,= value predicted by regression.

in predictive ability. The stepwise model with the single most important variables Cft ), still accounts for 65% of the variation in the Ro values. Ro is plot- ted against feed ratefin Fig. 4 and also against product of feed rate and temperature (ft ) in Fig. 5.

Limitations of the empirical models. The empirical models (Table 4) are valid only within a limited range of temperatures, ration levels and fish weights. Extrapolation of empirical relations can lead to erroneous results. For example, at t = 15 ‘C and w= 1 g, the multiple curvilinear model (Model 4) pre- dicts that oxygen consumption rate will increase as a function of ration up to a level of about 3% day- ’ but will decrease dramatically as ration levels approach the maximum level of about 6% day- ‘. This predicted effect is obviously unrealistic and is simply a result of lack of data at ration levels above 3% day- ‘.

Model 4 also gave unrealistic predictions at low ration levels. For example, at 0 ration, Ro was predicted to decrease as temperature increased. These difficulties limit the usefulness of the multiple curvilinear relationship as a general oxygen consumption rate model for juveniles. Data voids must be


__k

600 I I I I 1 I

l C&m - ouch - PuCm A PIT.20

o PBSk II NiCn - Pooled (o= 129)

500 -

. .

e 400 -

0’ 1 I 1 I I I I

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Ration level (%dry day’)

Fig. 4. Measured average daily oxygen consumption rate Ro (mg kg-’ h- ’ ) as a function of ration level (O/o dry food day-‘) for chum (Cm), coho (Co), sockeye (Sk) and chinook (Cn) salmon at Conuma (Co), Quinsam (Qu), Puntledge (Pu) and Nitinat (Ni) Hatcheries and by Brett and colleagues at The Pacific Biological Station (PB). The trend line is for the 129 pooled values (e0.682 ).

01 I I I I I I I 0 5 10 15 20 25 30 35

f*t (%dry day-‘“C)

Fig. 5. Measured average daily oxygen consumption rate Ro (mg kg-’ h-r ) as a function of the product ofthe ration level (% dry food day-‘) and temperature for chum (Cm), coho (Co), sockeye (Sk) and chinook (Cn) salmon at Conuma (Co), Quinsam (Qu), Puntledge (Pu) and Nitinat (Ni) Hatcheries and by Brett and colleagues at The Pacific Biological Station (PB). The trend line is for the 129 pooled values (r=0.807).


clearly delineated and filled if these relationships are to be useful predictive models.

Although the 129 measured values (Table 1) reflect a wide range of fish weights (0.65-33.3 g), temperatures (5-20°C) and ration levels (O-3.1% day- ’ ), the data are not evenly distributed over the experimental space. For example, all the data for small fish ( < 1.5 g) are concentrated around water temperatures of 6 and 10°C. Furthermore, no tish were fed below 1% day-’ or near the maximum ration as predicted by equation 14.

Similar problems exist with the distribution of data for intermediate sized (9.5-l 9.6 g) and larger (20-33 g) juveniles. The most obvious deficiency is a lack of data at the high ration levels theoretically possible at water temperatures over 12 ‘C.

Semi-empirical models. Because of data voids, these models used theoretical results to augment the existing set of data. Theoretical results were introduced at 0 ration and also at the maximum ration level. Maximum ration (jinax) was predicted from equation 14 (Stauffer, 1973 ) :

jinax=w-0.3333 (10.73 ln( l&+32)-37.71) (14)

where jinax = % dry food per day; w = fish weight (g ); t = temperature ( ’ C ) . Ro values at 0 ration level were calculated from the expression for standard metabolic rate (equation 11) and those at the maximum ration level were estimated by taking 60% of the active metabolic rate (equation 12). Data used to augment the existing set of measured values are shown in Table 6.

The values in Table 6 were pooled with the 129 measured feeding metabolic rate values to form an augmented data set. Both multiple curvilinear regression (MCR) and response surface analysis (RSA) (Schnute and McKinnell, 1984) were used to derive non-linear relations between Ro and weight (w), temperature (t) and ration level (j).

The MCR model is defined by entry 4 in Table 4. Values for the regression coefficients were I= 115.8436; J=47.9020; K= 1.6391; L = -5.1972; M= - 12.3847; N~0.0238; 0~0.0887; P=6.0036; Q=2.2760; R= -0.0234.

The RSA model is defined by the following equations involving the transformed variables (Schnute and McKinnell, 1984)

rl=p+qi& +& +q3t3 +rlI&*+r22t2*+r3353*

+ r12&r2+r13&5;+ r23<2<3 (15)

~i=(2~i-up~_u~i)/(~i_upi) (16)

&?= (2yY- vy-vY)/( vy-VY) (17)

That is, y is the response Ro (transformed to q, eq. 17) to the original x variables (transformed ri, eq. 16 ) , w (weight, i = 1 ), t (temperature, i= 2 ) and j


TABLE 6

Theoretical Ro values (derived from equations 1 I and 12) used to augment the existing set of measured feeding metabolic rate data

Weight

(9)

Temperature

(“Cl

Ration ( % dry food day- ’ )

Ro (mg kg-’ hh’)

IO IO IO 20 20 20 30 30 30 50 50 50

I 1

5 0 54.83 10 0 90.63 15 0 149.80 5 0 41.76

10 0 69.02 15 0 114.08 5 0 38.47

10 0 63.59 15 0 105.10 5 0 36.67

10 0 60.6 I 15 0 100.18 5 0 34.52

10 0 57.05 15 0 94.30 10 4.21 395 15 6.04 570

TABLE 7

Differences between measured and predicted estimates of Ro calculated from the 129 measured values in Table 1 and for the 146 values in the augmented data set (Table 1 plus Table 6)

Table I values (n= 129) Augmented data set ( n = 146 )

Model Mean diff. (mg kg-’ h-‘)

s.d. Mean diff. (mg kg-’ h-‘)

s.d.

RSA 1.03 34.19 1.44 32.63 MCR 0.69 34.98 0 34.48

(ration, i = 3 ) . Typical low and high values for y are ZJ and V and for x variables are uj and U,. Hence the predicted Ro is obtained from the backtransform

Ro= [ ( VY+vY+ (I/“- vy)q)/2 ]l’y (18) where

304

aI =0.8176527 a2 = 3.0500690 a,=0.6149418 y=O.3393800 p=O.6368755 q1 = 0.20782 15 q,=O.l829668 q3 = 0.9546940

rl,=0.2153913 r22= -0.1896812 r33= -0.2516344 r12= - 0.0549703 r,3=0.3698584 r,3=0.0425568 uI =0.651 {low w} U,=5 {low t}

W.E. MCLEAN ET AL.

?.43=0 (IOWJ)

U, = 50 {high w} U2=20 {high t}

U, = 6.04 {highs) U= 34.5 {low Ro} I/= 570 {high Ro} w=fish weight (g) t = temperature ( ‘C ) f= ration (% day- ’ )

The mean and standard deviation of the individual differences between measured and predicted Ro values were used to evaluate the models (Table 7).

The RSA model was slightly more biased than the MCR equation. How- ever, its s.d. was smaller and it was well-behaved at extreme ration levels. Hence the RSA model was accepted as the best overall predictor of Ro.

Oxygen consumption rates of adult salmon The oxygen consumption rates of adult salmon, unlike those of juveniles,

could not be easily related to the influence of environmental factors. Hence no attempt was made to model the Ro values of adult salmon. Not only were the data collected over too narrow a range of temperature and fish size, but the activity levels of adults held in these facilities were so variable that the effects of environmental factors were secondary.

Ro values for chum salmon at the Little Qualicum spawning channel were

100 - 0 0

.--.-0 0 I / I I I I

6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5

Temperature (“C)

Fig. 6. Measured average daily oxygen consumption rates for adult salmon (see Tables 2 and 3) as a function of temperature. Ro values (mg kg-’ h- ’ ) are contrasted with the standard and active metabolic rates calculated from equations 11 and 12.


very high. These fish either were moving upstream or were engaged in spawning. Furthermore, water velocities in the spawning channel ranged between 46 cm s-l (1.5 ft s-*) and 61 cm s-l (2 ft s-l) depending on water flow. Thus, even if fish were simply holding position in the current, their metabolic rate would be elevated.

The average oxygen consumption rate for chum salmon at this site was 283 mg kg- ’ h- ’ (sd. = 43, n = 20). Rates were high enough that even at the maximum water flow, oxygen concentrations often fell below 6 mg 1-l for extended periods. Rate measurements were made at water temperatures ranging between 7.1 and 9.9”C. The average weight of chum salmon in the channel was 4.5 kg.

Oxygen consumption rates were much lower at the Big Qualicum holding facilities. There, measurements were made on chinook salmon at approximately 9 ‘C, and the average weight of the fish was 10 kg.

However, rates were elevated for short periods during fish culture operations such as crowding and sorting. Ro rates ranged between 35 mg kg-’ h- ’ for fish holding quietly to 22 1 mg kg- ’ h- ’ for active fish that had just moved from the Iishway into the holding pond. As the average water velocity in the pond was only 3.7 cm s- ’ (0.12 ft s- I ), the resting metabolic rates would be expected to be low.

Ro values increased to 122 mg kg- ’ h- ’ during crowding operations. It was noted during a disturbance that the oxygen consumption rate increased very quickly and then recovered slowly over several hours.

Measured Ro values are contrasted with the standard and active rates (eqs. 11 and 12 ) in Fig. 6. Average daily rates for actively migrating and spawning chum salmon were approximately half of the active rate while chinook salmon holding in quiet water consumed oxygen at about 1.7 times the standard rate.

CARRYING CAPACITY MODEL FOR JUVENILES

Model components

Prediction of carrying capacity. Carrying capacity is defined here as the maximum biomass of fish that could be reared in a pond while acceptable oxygen concentrations are still maintained at the outflow. An idealized model was derived by substituting the peak daily oxygen consumption rate (Ro) into equation 6 (Lr= (Ci- C,) 60/Ro) to obtain the maximum allowable load rate Lr. This value is an estimate of the maximum biomass of Iish (kg) that can be reared at a given water flow (1 min- ’ ). Equation 6 also requires input of the oxygen concentration at the inflow (C,) and specification of an acceptable oxygen level at the outflow of the pond ( C,).

InjZow oxygen concentration. It is convenient to express the inflow oxygen


concentration (mg 1-l) C, as a function of the saturation level so/o and the oxygen concentration at saturation C’s; Ci = 5% C’s/ 100. The oxygen concentration of water in equilibrium with the atmosphere (Cs) was related to temperature, barometric pressure and salinity by Hitchman ( 1978 ). If the molec- ular weight of oxygen gas is 3 1.9988 g, the fraction of oxygen in dry air is 0.20946 and the molar volume is 22.4 14 1 (Chemical Rubber Co., 1974) then

Cs=0.39346A (BP-Pw) (19)

where: BP = barometric pressure (mm Hg ) ; Pw = water vapour pressure (mm Hg ); A = Bunsen coefficient for oxygen; C’s= saturation concentration of oxygen (mg 1-l ); and 0.39346 = factor which allows C’s to be expressed in mg 1-l.

Pw is the water vapour pressure of the atmosphere in equilibrium with li- quid water and is a function of temperature (Shrimpton, 1975 ) :

Pw=760exp[Pl -P2/t”K+P3 t”K-9 ln(t”K)]+0.002 (20)

where: Pw=water vapour pressure (mm Hg); Pl = 70.4346943; P2 = 7362.698 1; P3 =0.006952085; and t”K= temperature in degrees kelvin=t+273.16.

The Bunsen coefficient (A) is defined as the volume of oxygen (ml), re- duced to 0°C and 1 atm pressure, which at the temperature of measurement, is dissolved in 1 ml of water when the partial pressure of oxygen is 760 mmHg. “A” is a function of temperature (t) and salinity (Su), and is given by (Hitchman, 1978) as

A=O.OOl (Al +A2 t+A3 t2+A4 t3+A5 t”) -0.001 [ (Su

where:

-0.03)/1.805] (Sl+S2 t+S3 t2+S4 t3+S5 t”) (21)

Al =49.01 A2= - 1.335 A3 =0.02759 A4 = - 0.0003225 A5=0.000001614 t = temperature ( ’ C ) A = Bunsen coefficient for oxygen

S1=0.5516 S2= -0.01759 S3=0.0002253 S4 = - 0.0000002654 S5 =0.00000005362 Su = salinity ( ppt )

Therefore, substituting the expressions for A (equation 2 1) and Pw (equation 20) into equation 19 gives an expression for C, in terms of temperature, barometric pressure and salinity.

Acceptable oxygen concentrations. The oxygen concentration at the pond outflow (C’) was set according to the criteria of Davis ( 1975), whereby three


levels of protection (A, .B and C ) are derived reflecting variation in tolerance of individual fish within a population. Level A satisfies the oxygen requirements of most of the individuals in a population, level B satisfies the average fish while level C meets the needs of only a small fraction of the population. At the lowest level most fish experience sublethal effects of oxygen deprivation.

The Davis criteria are based on mass transfer of oxygen across the gills. Since the transfer rate depends on both the partial pressure gradient (between the ambient water and blood plasma) and the oxygen concentration of the ambient water, both parameters must be satisfied to meet a specific level of protection. Ambient oxygen concentration and partial pressure must be at least 7.75 mg l- ’ and 120 mm Hg to meet level A; 6 mg 1-l and 90 mm Hg for level B and 4.25 mg l- ’ and 60 mm Hg for level C (Davis, 1975 ) .

Because these criteria put limits on both oxygen partial pressure and concentration, they vary with water temperature. Ambient oxygen concentrations required to meet levels A, B and C are shown as a function of temperature in Table 8. Level B is accepted as a minimum standard for hatcheries producing high quality smolts for release to the ocean.

Definition of safe oxygen consumption rates. The Ro value used to calculate carrying capacity must also be carefully chosen. If the estimate of Ro is too low, the predicted carrying capacity will be too high and the fish will experience oxygen concentrations below the desired level. Hence it is better to use an estimate of Ro that is somewhat higher than the actual oxygen consumption rate. As noted previously however, the active metabolic rate of salmon is so high that even in well planned rearing programs there is always the possi- bility that extreme bursts of activity could result in dangerously low levels of dissolved oxygen. Setting the carrying capacity in anticipation of such an un- likely event is not practical; we recommend that Ro be chosen to include most of the consumption rates likely to be encountered in typical rearing operations.

The Ro values generated by the predictive models are average daily rates.

TABLE 8

Ambient oxygen concentrations required to meet Davis ( 1975) level A. B and C criteria as a function of temperature

Temp. (“C) Protection level (mg I- ’ ) Temp. (“C) Protection level (mg I-‘)

A B C A B C

5 9.69 7.21 4.84 15 7.75 6.00 4.25 7 9.22 6.92 4.6 1 17 7.75 6.00 4.25 9 8.79 6.59 4.40 19 7.75 6.00 4.25

II 8.40 6.30 4.25 13 8.04 6.03 4.25


The peak daily consumption rate (over the most active 2 h of the day) was found by multiplying the average daily rate by the peak-to-average ratio. These ratios were quite variable with a mean of 1.2048 and a standard deviation of 0.075 (n = 73 ). The peak daily oxygen consumption rate was calculated from

Peak daily Ro = 1.2048 x (average daily Ro) (21)

The uncertainty in this calculated value can be found by combining the uncertainties in the peak-to-average ratio and the predicted average daily Ro. The standard deviation, s.d .1 =0.075, was used to quantify the uncertainty in the peak-to-average ratio. Uncertainty in the average daily Ro value was estimated from the standard deviation (s.d.2) in the difference between measured (Mi) and predicted (Pi) values. This was found by calculating the standard deviation of the difference (Mi- Pi) for the 129 measured Ro values: [sum(Mi-Pi)2/128]0.5. Ifthe RSA model (equation 18) is used to predict the average daily Ro value, s.d.* is 34.19 (Table 7).

These standard deviations (s.d .,=0.075 and s.d.2=34.19) can be combined to quantify the uncertainty in the predicted peak daily oxygen consumption rate. The standard deviation associated with this value (s.d.p) was calculated from Baird ( 1963)

s.d.p= 1.2048 Ro [ (s.d.,/1.2048)2+ (s.d.2/Ro)2]0.5 (23)

where Ro=average daily Ro value predicted by equation 18, s.d., =s.d. of peak-to-average ratio (0.075 ) and s.d.z = s.d. of difference between measured and predicted Ro ( 34.19 ). The safe oxygen consumption rate was defined as one standard deviation above the predicted peak daily rate

Safe Ro= 1.2048 Ro+s.d.p. (24)

If the average daily Ro value as predicted by equation 18 was 24 1 mg kg- ’

h- ’ then the peak value would be 1.2048 x 24 1 = 290 mg kg-’ h- ’ and its standard deviation would be 45 mg kg- ’ h- ‘. The safe oxygen consumption rate would be 290+45=335 mg kg-’ hh’.

To predict the maximum load rate with a margin of safety, the safe Ro ( 1.2048 Ro+s.d.p) was substituted into equation 6:

Lr=60 (Ci-C’)/( 1.2048 Ro+s.d.p) (25)

where s.d.p= s.d. of peak daily Ro value (equation 23) and Ci, C’ Lr and RO

are as previously defined. This load rate is considered “safe” as the oxygen concentration specified at the pond outflow (C’) would be satisfied most of the time.

In the previous example the average daily oxygen consumption rate was 241 mg kg- ’ h- ’ and the consumption rate actually used to predict a maximum safe load rate was 335 mg kg- ’ h- ‘. If the inflow oxygen concentration is 10.5 mg l- ’ and the acceptable outflow concentration is 6 mg 1-l) the max-


imum allowable load rate would be Lr= (10.5-6) x 60/335=0.81 kg 1-l min.

Model predictions Carrying capacities calculated from equation 25 are shown in Table 9 over

a range of culture conditions. These calculated values assume a barometric pressure of 760 mm Hg, zero salinity and a percentage oxygen saturation of the inflow of 95%. These loads are considered “safe” as the specified oxygen criterion will be satisfied most of the time. This model gives reasonable predictions of carrying capacity for fish under 40 g, water temperatures between 5 and 20 ‘C and at ration levels between 0 and maximum ration (equation 14).

Limitations of the juvenile model The water flow requirement model presented here is based solely on the

oxygen concentration requirements of rearing fish. This idealized model assumes that if the water flow rate is sufficient to meet oxygen needs, then ac- cumulations of ammonia, suspended particulate matter (waste food and feces) and carbon dioxide will not be harmful.

This assumption can easily be violated if water quality is initially poor. It may also be inaccurate if feed rates exceed the appetite of the fish or when feeding is initiated in newly emerged fry. In these cases uneaten food may increase suspended solid levels to the point where gill damage occurs (Banks et al., 1979). That is, water flow rates that satisfy oxygen requirements may not be sufficient to dilute suspended solids to acceptable levels. The model developed also assumes that the flow is uniformly distributed so that the outflow has the lowest oxygen concentration in the pond. However, if flow distribution is poor, the predicted water flow requirements will not protect the fish - localized areas in the pond may have much lower oxygen concentrations than predicted by the idealized model.

Another important consideration in setting water flow requirements, not included in the present model, is the effect of flow rate on the water velocities experienced by the fish. The water flow rate, along with the shape of the pond and nature of the inflow and outflow structures, determines both the distribution of flow and the magnitude of the velocities in the pond. Velocities may have an important influence on fish health. It is well known that fish condi- tion, susceptibility to ectoparasites and exposure to suspended solids are affected by water velocity.

CARRYING CAPACITY MODEL FOR ADULTS

The adult data presented in this report are too limited for development of a general carrying capacity model. However, some inferences can be made.

TA

BL

E

9

Car

ryin

g ca

paci

ties

in k

g of

fis

h I-

’ m

m

of w

ater

fl

ow

( Max

Lr)

at

vari

ous

tem

pera

ture

s,

indi

vidu

al

fish

w

eigh

ts

and

ratio

n le

vels

. V

alue

s ar

e ge

nera

ted

to

mee

t le

vel

A,

Ban

d C

oxy

gen

crite

ria

(Dav

is,

1975

) w

hen

the

infl

ow

satu

ratio

n le

vel

is 9

5%

and

baro

met

ric

pres

sure

is

760

m

m

Hg.

A

vera

ge

daily

R

o va

lues

(mg

kg-

I h-

’ ) c

alcu

late

d fr

om

equa

tion

18 (

RSA

) ar

e al

so

show

n

wt

Tem

p.

Rat

ion

k)

(“C

) (%

dryd

ay-‘

)

1 5

0 I

5 1.

07

1 5

2.14

10

5

0 10

5

0.50

10

5

0.99

20

5

0 20

5

0.39

20

5

0.79

1

10

0 1

10

2.13

1

10

4.27

10

10

0

10

10

0.99

10

10

1.

98

20

10

0 20

10

0.

79

20

10

1.57

1

15

0 1

15

3.02

I

I5

6.04

IO

15

0

10

15

1.40

10

15

2.

80

20

15

0 20

15

1.

11

20

15

2.23

Max

Lr

Do

Max

Lr

DO

M

axL

r D

O

LvA

L

vA

LvB

L

vB

LV

C

LV

C

(kgl

-‘m

in)

(mg

I-‘)

(k

gl-’

m

in)

(mgl

-‘)

(kg

1-l

min

) (m

g I-

‘)

1.06

9.

7 2.

12

7.3

3.18

4.

8 0.

51

9.7

1.03

7.

3 1.

54

4.8

0.40

9.

7 0.

80

7.3

1.21

4.

8 1.

36

9.7

2.72

7.

3 4.

08

4.8

0.75

9.

7 1.

50

7.3

2.25

4.

8 0.

58

9.7

1.16

7.

3 1.

75

4.8

1.53

9.

7 3.

07

7.3

4.60

4.

8 0.

85

9.7

1.70

7.

3 2.

55

4.8

0.64

9.

7 1.

29

7.3

1.93

4.

8 0.

80

8.6

1.62

6.

4 2.

43

4.3

0.31

8.

6 0.

62

6.4

0.94

4.

3 0.

25

8.6

0.50

6.

4 0.

75

4.3

1.03

8.

6 2.

08

6.4

3.14

4.

3 0.

44

8.6

0.90

6.

4 1.

35

4.3

0.33

8.

6 0.

66

6.4

0.99

4.

3 1.

17

8.6

2.37

6.

4 3.

57

4.3

0.49

8.

6 1 .

oo

6.4

1.50

4.

3 0.

35

8.6

0.71

6.

4 1.

07

4.3

0.52

7.

8 1.

03

6 1.

53

4.3

0.18

7.

8 0.

36

6 0.

54

4.3

0.15

7.

8 0.

31

6 0.

46

4.3

0.68

7.

8 1.

34

6 2.

00

4.3

0.26

7.

8 0.

51

6 0.

76

4.3

0.19

7.

8 0.

37

6 0.

55

4.3

0.78

7.

8 1.

55

6 2.

31

4.3

0.29

7.

8 0.

56

6 0.

84

4.3

0.20

7.

8 0.

39

6 0.

58

4.3

Ro (m

g kg

-’

h-r)

79

198

262 54

12

6

171 44

107

152 96

30

1

382 67

200

283 55

17

6

261

137

448

531 97

310

434 80

27

6 40

9


At Little Qualicum spawning channel the carrying capacity of the water supply was calculated by solving equation 7 for the Load rate Lr.

(26)

where symbols are defined in equation 7. The maximum load rate and number of 4.5 kg fish that could be supplied with oxygen at two different water flow rates are shown in Table 10. These projections were made for three outflow oxygen concentrations (Level C=4.4, Level B= 6.7 and Level A= 8.9 mg 1 - ’ ); an Ro value of 326 mg kg- ’ h- ’ (the mean of values in Table 7 + 1

s.d. ); a temperature of 8.5 ‘C and an inflow oxygen concentration of 11.1 mg I- ’ (95% of saturation).

The oxygen consumption rates of chinook held at Big Qualicum were more variable (range 35 to 22 1 mg kg- I h- ’ ) making the calculation of carrying capacity more uncertain. To incorporate a margin of safety, the highest measured rate (22 1 mg kg- ’ h- ’ ) was used to calculate the carrying capacity for holding chinook. With an inflow oxygen concentration of 10.8 mg l- ’ (95% of saturation) and a temperature of 9.5 ‘C, the maximum allowable load rates to meet level A (8.7 mg l-l), B (6.5 mg I-‘) and C (4.4 mg 1-l) oxygen criteria were 0.6, 1.2, and 1.8 kg l- ’ min- I, respectively.

These measurements support the general criterion for adult holding of 1.2 kg 1-l min proposed by Shepherd ( 1984). The results at BQ suggest that this criterion should protect fish from low oxygen concentrations except during exceptional circumstances. It must be recognized that adults have high active metabolic rates (equation 12) and that disturbances can induce a very rapid increase in the oxygen consumption rate and hence an equally rapid drop in

TABLE 10

Little Qualicum spawning channel carrying capacities (kg of fish I-’ min) at flow rates of 76 455 1 min-’ (45 cfs) and 101 941 I min-’ (60 cfs) and for outflow oxygen concentrations (Cr) meeting level A, B and C oxygen criteria (Davis, 1975 )

Maximum load rates (kg 1-l min)

Flow rate Level A (1 mitt-‘) (8.9 mgl-‘)

Level B (6.7 mgl-I)

Level C (4.4mgl-‘)

76 455 0.39 I .oo 1.49 (6604)* (17 012) (25 257)

101 941 0.37 0.96 1.43 (8359) (21 768) (32 390)

*Number of fish, based on average fish weight of 4.5 kg, shown in brackets.


the ambient oxygen concentration. Therefore, fish at the downstream end of a pond could experience very low oxygen levels for extended periods if the pond population is disturbed.

The adult holding criterion ( 1.2 kg l- ’ min) is not applicable to adults in spawning channels (Table 10). Activity levels are so high that a greater water flow is required if reasonable oxygen levels are to be maintained. Further- more, low oxygen concentrations may be more critical for spawning channels than for adult holding operations. Marginal dissolved oxygen concentrations of 5 to 6 mg l- ’ at the downstream end of the Little Qualicum channel have hindered upstream movement and deterred spawning activity.

ACKNOWLEDGMENTS

We especially thank the late Dr. J.R. Brett for the advice, guidance and on- going support he provided for this work. Dr. Brett developed much of the biological framework for the effects of temperature on respiration, activity and growth upon which this paper is based. We are also grateful to Dr. J. Colt for his valuable comments regarding the calculation of Ro. Also acknowledged are Bruce Shepherd for reviewing the manuscript, Joan Bennett for assistance in preparing the data and Ted Sweeten for his help in acquiring the 24-h oxygen profiles required for this study. The assistance of staff at Con- uma, Puntledge, Quinsam, Big Qualicum, Nitinat and Little Qualicum salmon enhancement facilities, who helped in the collection of data, is also gratefully acknowledged.

REFERENCES

A.P.H.A. (American Public Health Association. American Water Works Association and Water Pollution Control Federation), 1980. Standard Methods for the Examination of Water and Wastewater, 15th edn. Washington, DC, 1134 pp.

Baird, D.C., 1963. Experimentation. Prentice-Hall Inc., London, 198 pp. Banks, J.L., Taylor, W.G. and Leek, S.L., 1979. Carrying capacity recommendations for Olym-

pia area national fish hatcheries. Abernathy Salmon Cultural Development Centre, 57 pp. Brett, J.R., 1964. The respiratory metabolism and swimming performance of young sockeye

salmon. J. Fish. Res. BoardCan., 21(5): 1183-1226. Brett, J.R., 1965. The relation of size to rate of oxygen consumption and sustained swimming

speed of sockeye salmon (Oncorhynchus nerka). J. Fish. Res. Board Can., 22 (6): 149 l- 1501.

Brett, J.R., 1976. Feeding metabolic rate of young sockeye salmon, Oncorhynchus nerku, in relation to ration level and temperature. Fish. Mar. Serv. Res. Dev. Tech. Rep. 675: 43 pp.

Brett, J.R., 1979. Environmental factors and growth. In: W.S. Hoar and D.J. Randall (Editors), Fish Physiology Vol. VIII. Academic Press, New York, NY, pp. 599-675.

Brett, J.R. and Glass, N.R., 1973. Metabolic rates and critical swimming speeds of sockeye salmon (Oncorhynchus nerka) in relation to size and temperature. J. Fish. Res. Board Can.. 30( 3): 379-387.


Burrows, R.E. and Chenoweth, H.H., 1970. The rectangular circulating rearing pond. Prog. Fish- Cult., 32: 67-80.

Chemical Rubber Company, 1974. Handbook of Physics and Chemistry, 55th edn. CRC Press Inc., Cleveland, OH.

Clark, J.W., Warren, V. and Hammer, M.J.. 197 1. Water Supply and Pollution Control. Inter- national Textbook Company, Scranton, PA.

Colt, J. and Orwicz, K.. 199 1. Modeling production capacity of aquatic culture systems under freshwater conditions. Aquacult. Eng., 10: l-29.

Davis, J.C., 1975. Minimal dissolved oxygen requirements of aquatic life with emphasis on Canadian species: a review. J. Fish. Res. Board Can., 32: 2295-2332.

Gromiec, M.J., 1989. Reaeration. In: S.E. Jorgensen and M.J. Gromiec (Editors), Mathemati- cal Submodels in Water Quality Systems. Elsevier, Amsterdam, pp. 33-64.

Hitchman, M.L., 1978. Measurement of dissolved oxygen. Wiley Interscience, New York, NY, 255 pp.

McLean, W.E., 1979. A rearing model for salmonids. M.Sc. Thesis, University of British Co- lumbia, Vancouver, B.C.. 134 pp.

Priede, I.G., 1985. Metabolic scope in fishes. In: P. Tytler and P. Calow (Editors), Fish Ener- getics. John Hopkins University Press, Baltimore, MD, pp. 33-64.

Schnute, J. and McKinnell, S., 1984. A biolgically meaningful approach to response surface analysis. Can. J. Fish. Aquat. Sci., 41: 936-953.

Shepherd, B.G., 1984. The biological design process used in the development of federal govern- ment facilities during Phase I of the Salmonid Enhancement Program. Can. Tech. Rep. Fish. Aquat. Sci., 1275: 188 pp.

Shrimpton. N., 1975. Dissolved gas program designed in 1975 by Mr. Neil Shrimpton, for use on WANG-SOOTP. Draft. Pollution Control Branch, Environmental Protection Service, Ministry of the Environment, Victoria, B.C., Canada.

Spain, J.D., 1982. Basic Microcomputer Models in Biology. Addison-Wesley Pub]., London, 354 pp.

Stauffer, G.D., 1973. A growth model for salmonids reared in hatchery environments. Ph.D. Thesis, University of Washington, Seattle, WA, 2 13 pp.

Steffensen, J.F., 1989. Some errors in respirometry of aquatic breathers: how to avoid and cor- rect for them. Fish Physiol. Biochem., 6( 1 ): 49-59.

oxygen consumption rates and water flow requirements of pacific salmon (oncorhynchus spp.) in the...

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