t4t5NOTES

Growth and Survival of Hailitock (Melanogranxmus aeglefrnus)Larvae in Relation to Planktonic Prey Concentration

Gnorrnnv C. L.tunnNcr

National Marine Fisheries Service, Northeast Fisheries CenterNarragansett Laboratory, Narragansett, R.I. 02882' USA

LaunrNcr, G. C. 1974. Growth and survival of haddock (Melanogrammus aeglefinus)larvae in relation to planktonic prey concentration. J. Fish. Res. Board can.3l: 1415-1419.

When newly hatched haddock (Melanogrammus aeglefinus) larvae were fed zoo-plankters at nominal rates of 0.5, 1.0, and 3.0/m1 in the laboratory at7 C, they grew atsimilar rates. After 6 wk, they averaged 8.7, 10.0, and 11.2 mm in standard length and810, 1300, and 1728 pg in dry weight, and had condit ion factors of 1.25, 1.22, and 1.32.

when fed at 0 . 1 and 0.01 plankters/ml, all larvae died in 3 and 2 wk; at 0. 5-3 .0 plank-

ters/ml, daily instantaneouJ mortality coefficients were 0.06-0.02 during 6 wk. Larvaebegan feeding 2 days after hatching, and the point of no leturn after they were deprivedof-food *u. Z duy. after hatching, yolk absorption being completed on day 6 or 7. A1llarvae deprived offood until B and 10 days after hatching, although initiating feeding' didnot survive another 4 days. Prey concentration also influenced delayed feeding with greaterpercentages of larvae abie to initiate feeding at higher plankton 1evels on the point-of-no-return day.

LaunpNcr, G. C. 1974. Growth and survival of haddock (Melanogrammus aeglefinus)larvae in relation to planktonic prey concentration. J. Fish. Res. Board can.3l:1415-1419.

Les larves d'aiglefln (Melanogrammus aeglefinus) nouvellement 6closes croissent au

m6me rythme, lorsque nourries d- zooplankton d des taux nominaux de 0.5, 1.0 et 3'0organismes/ml en laboratoire i 7 C. Au bout de 6 semaines, elles ont en moyenne unelongueur standard de 8.7, 10.0 et 11 .2 mm, un poids sec de 810, 1300 et 7728 pg, et windice d'embonpoint de l :25,1.22 eI 1.32. Nourries d des taux de 0.1 et 0.01 organismes/ml, toutes les lirves meurent au bout de 3 et 2 semaines; d des taux de 0.5-3.0 organis'mes/ml, Ies coefficients de mortalit6 instantan6e sont de 0.06-0.02 pendant 6 semaines.Les larves commencent d se nourrir 2 jours aprds 6closion, et le point critique, sans retourpossible, lorsqu'elles sont priv6es de nourriture, se situe d 6 jours aprds 6c1osion,lat6-sorption du vitellus 6tant cbmpldte au jour 6 ou 7. Toutes les larves priv6es de nourriturejus[u'd 8 et 10 jours aprds 6closion, bien qu'elles commencent d se nourrir, meurent aprbs+ jour. additionnels. La concentration des proies affecte 6galement I'alimentation diff6r6e'un plus fort pourcentage de larves 6tant capables de commencer d se nourrir au jour critiquelorsque les concentrations de plancton sont plus 61evdes.

Received February 11, 1974Accepted May 15, 1974

Requ le ll f6vrier,1974Accept6 le 15 mai, 1974

Ir has been demonstrated for haddock (Melano- plankters/ml) on growth, survival, and conditiongrammus aeglefinus) that alargedifferential mortality factor during the first 6 wk after hatching, and theoccurs during the planktonic larval stage which time larvae could suryive in the absence of foodmay affect thi recruit level of a year-class (Parrish and still retain the ability to initiate successful1950; Saville 1956). Likely causes oflarge differential feeding (point of no return).mortalities between years are the availability of asuitable food supply in sumcient quantity u.tA th" .Matetials and.methods -Fertilized eggs were ob-

critical timing involved between prey encountere.n tained from a pair of naturally spawning adults in the

feeding initiation. This research was d"sig.red'iI 56,700-liter experimental aquarium of the Narragansett

examine the innuence of nve nominar pr;kto;i; Hlil3i?i?;il3:'.r:Tffiit[l;$ H1[363#ir]ff:!?:prey concent ra t ions (3 .0 , 1 '0 ,0 .5 ,0 '1 , and 0 .01 (approx imatedvo lumet r ic -a l l y )werep laced inseawater

(29/ss) in each of five 37.8liter all glass aquaria paintedPrinted in Canada (J3312) black for the prey concentration studies. For the point-Imprimd au Canada (J3312) of-no-return studies, 100 newly hatched larvae were

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1416 I. FISH. RES, BOARD CAN., VOL, 31(8), 1974

placed in 3.8liter plastic aquaria painted black. Allexperimental aquaria were provided with airstones,and the temperature was maintained at 7 t 0.5 C.Photoperiod lvas manipulated to approximate thenormal day:night ratio during the haddock spawningseason.

Zooplankton concentrations (Fig. 1) were establishedat hatching by maintaining a constant volume of seawater in each aquarium and adding the desired numberof plankters. Counts for the concentrations werebased on the mean of duplicate 5-ml samples from eachaquarium after gentle stirring. Concentrations weremaintained generally near the nominal values by adding,every day or every second day, known quantities ofzooplankton taken with 35-iz mesh plankton nets fromthe Narragansett Bay area and sieved through 210-pmesh strainers. The addition of sea water with zoo-plankton caused the salinity to vary between 28 and307n dwing the experiment.

The zooplankters were mainly nauplii of Acartiaclausi, Centropages hamatus, and Balanus balanoidesand included some adults of A. Clausi and Podon sp.,all known as food items of larval haddock in fie1dstudies (Marak 1960; Ogilvie 1938).

As all eggs and larvae came from the same spawning,initial dry weights and standard lengths were measuredon the basis of a sample of 10 larvae (two from eachof the five experimenial aquaria) taken before foodwas introduced. Thereafter, 10 larvae from each ofthe experimental concentrations were collected every7 days for measurements. Dry weight was determinedby rinsing larvae in distilled water, pipetting onto aglass petri dish, drying to a constant weight at 90 Cfor 24 h, and weighing individually to the nearest 0.1pg on a Chan Gram electrobalance. Standard lengthswere measured to the nearest 0.1 mm with a filarocular micrometer in a dissecting microscope.

Condition factors were measured weekly after yolkwas absorbed and were calculated by dividing the mean

l* l

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E ,"ri , "1

3 t 2

D A Y O F E X P E R i M E N '

Ftc. I. Monitored plankton concentrations for thefive nominal concentrations (in parentheses) for theduration of the experiment. Horizontal lines representmean monitored values.

dry weight (pg) by the cube of the mean standardlength (mm).

Average daily instantaneous mortality coefficientswere calculated from the formula:

- log, 51 - log, Syt : -T ( r )

where Ss and Sr, are the numbers of survivors at thebeginning and end of the time interval in days (T).Numbers surviving at the beginning of T were cal-culated from studies of G. C. Laurence and C. A.Rogers (unpublished data) which indicated that 353of 1000 fertilized haddock eggs hatched when subjectedto 7 C and 28Voo, and numbers surviving to the endof T were determined by actual count. To correct S1for potential survivors that had been removed in thesampling, the following formula was used:

$ ' : s r+ r c f e - z r z Q )h- l

where 10 : number of individuals removed each week,w : number of weeks of sampling, 7 : days in 1 wk,Z : ayeraEe daily instantaneous mortality coeffi-cient.The initial Z value in equation (2) was chosen to

reflect the maximum possible mortality rate, i.e. nosurvivors from the samples taken, and was used toiteratively correct Sy in equation (1) so as to give anunbiased estimate of Z for each experiment.

Daily specific growth rates were calculated fromthe formula:

SGR _ 1OOLogu GT - Logu Gr

T

where GT and G; are the sizes (mean dry weight) atthe beginning and end of the time interval in days (T).

The point-of-no-return experiment was designed todetermine the latest point after hatching when foodhad to become available for the larvae to initiatesuccessful feeding. Larvae in separate aquaria werefed ad libitum (approximately 2 plankterslml) startingat successive 2-day intervals from hatching, andsamples of 10 larvae were taken every 24 h after feedingand analyzed for stomach contents to determine wben50/6 or more fed or it was obvious that larvae couldnot feed successfully. Then an experiment was set upat the 5 plankton concentrations in the feeding levelstudies to determine if plankton concentration on theday of the point of no return affected feeding capability.

All statistical analyses of the growth data used inthese experiments are described in Steel and Torrie(1e60).

Mortality - Daily instantaneous mortality coeffi-cients for the duration of the experiments from hatchingdecreased with increasing feeding level at 3.0, 1.0,and 0.5 pl/ml. The total numbers of survivors and theunbiased coefEcients for the three prev concentrationswere:

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Concn (pl/ml) 3.0No. of survivors 139Coefficient (z) 0.02

Mortality was 70A/6 at 0.1 and 0.01 p1/m1 in 2 and 3wk.

When larvae were deprived of food until 8 and 10days after hatching and then provided with planktersad libitum, all died within another 4 days even thoughmore than 507o had, food in their alimentary tracts.Larvae deprived of food until day 12 after hatchingwere all dead on day 12 apparently of starvation.Yolk absorption was complete on day 6 or 7, and 507oor more of the larvae deprived until days 2, 4, and 6all initiated feeding and remained healthy to day 14when observations ceased. These results indicatedthat day 6 after hatching was the point of no return,and that the criterion of 50/6 feeding initiation wasnot necessarily valid for haddock larvae without sub-sequent observation.

The percentages of larvae that fed on day 6 at the5 prey concentrations and subsequently survived were:

C o n c n 3 . 0 1 . 0 0 . 5 0 . 1 0 . 0 1/6 feeding 80 60 50 30 10

Growth - On the basis of the semilogarithmictransformations of the growth in mean dry weightand mean standard length vs. weeks after hatchingand the slopes of the regression equations (Fig. 2),growth at 0 . 5-3 .0 pl/ml tended to inqease (P > 0 . 05)with prey concentration. Of course, the total mortalityat concentrations of 0.1 and 0.01 p\/ml negated anygrowth at these feeding levels.

Condition factors of larvae increased with time forall feeding levels (Fig. 2), the rates of increase beingrandomly associated with feeding level.

Discussion - Relating mortality estimates of theseexperiments to those determined in laboratorystudies of other species reveals some similarities.O'Connell and Raymond (1970) working withnorthern anchovy (Engraulis mordax) larvae re-corded high mortalities at concentrations of 0. 1copepod nauplius/ml and below, as in these studies.Saksena and Houde (1972) found variable survivalof bay anchovy (Anchoa mitchilli) and scaled sardine(Harengula pensacolae) larvae in the laboratory,but concluded that prey concentrations of 0.5-1.0copepod naupliusiml provided adequate food forgrowth and survival.

The mortality percentages noted for prey con-centrations of 0.1-3.0 pl/ml in this research aresimilar to field estimates noted by other researchers.Saville (1956) recorded field estimates of dailymortality percentages for haddock larvae frcmhatching to 10-21 mm in size, which approximatesthe sizes of haddock in this research. His estimatesfor 2 yr range from 4.8 to 10.77o. A calculation

t4 l7

based on Colton's (1965) field data for GeorgesBank larval haddock produced mortality rates of6.5-:7.1%lday. This may indicate that the presentlaboratory studies approximate conditions in thenatural environment.

The fact that condition factor at each of thethree higher feeding levels increased with timeindicated a disproportionate increase in dry weightgrowth as compared with the cube of standard lengthgrowth. Blaxter (1965) also noted an increase incondition factor in healthy herring larvae andattributed it to the result of allometric growth andthe addition of skeletal structures. The interpretationof condition factors is apt to be difficult; however,it does give a basis for comparison of the treatments(planktonic-prey concentrations) in these experi-ments.

The speciflc growth rates in standard lengthcomputed in these laboratory studies at 7 C fromthe data of Fig. 2 were 1 .12, 0.99, and 0.857oldayat 3.0, 1.0, and 0.5 pl/ml. These rates, especiallyat 3.0 pl/m1, are similar to results of Saville (1956)who estimated larval haddock growth rates interms of length from field data. His computedgrowth coemcient (no temperature data given) for40-45 days after hatching was 0.0118, or a specificgrowth rate on a daily basis of t.l8%' These arealso very similar to the growth rate of 1'.15%ldaycalculated by Saville from Walford's (1938) fieldresearch. In view of the 100% mortality at con-centrations of 0. 1 and 0 .01 pl/ml and the similarityof these laboratory growth rates to the computedfield estimates, it appears that haddock larvae mayneed prey concentrations of 0.5-3.0 pl/ml forsuitable growth.

The results of this laboratory research corroborateseveral field investigations in which prey concentra-tions encountered by larvae were directly relatedto their abundance or survival. Lisivnenko (1961)noted that in years when plankton organisms wereless than 0.01 pl/m1 larval Baltic herring werescarce in field collections, and in years when con-centrations were higher than 0.01 pl/ml larvaewere much more abundant. The same relationshipwith an apparent critical density of 0.01 pl/ml wasrecorded for the Black Sea anchovy (Pavlovskaya1961). Sysoeva and Degtereva (1965) reported thatthe minimum abundance of Calanus finmarchicusin the plankton when the intensity of feeding of codlarvae decreased was from 0.01 to '005/m1, andthat a concentration of 0.02/ml provided sufficientfood for good survival. Bogorov (1939) discoveredthat cod larvae were much more abundantly asso-ciated 'uvith water masses where the number ofcopepod nauplii was 0.01/ml than at lower con-centrations.

1 . 0790 .03

0 . 51 l0 .06

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1418 J. FISH. RES. BOARD CAN., VOL. 31(8), 1974

The above field study estimates of prey concentra-tions indicate larval success for some species at con-centrations somewhat lower than indicated forhaddock in this laboratory study. However, thefield study prey concentrations represent averagedensity over a linear or oblique distance sampledby a plankton net. Copepods have contagious

3.O PLlHL --- t r

t .o PL/ i lL -o

o .5 PL IML - ' - o

distributions and larvae may well be associatedwith clumps of prey that are more densely con-centrated than indicated in a plankton tow madeover some arbitrary distance. The range of densitiesin this experiment may approximate at least a partof the range of densities encountered by larvalhaddock in contagiously distributed plankton.

E$, ao.oIF(tzlrl

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2000

LoG Y. l .5 l+O.a8r

, \LOG Y. l.6l+0.22r

LOG Y. 1 .59+O.25r

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WEEK AFTER HATCHING

Ftc. 2. Dry weights, standard lengths, and condition factors in relation toweek after hatching of haddock larvae fed at three zooplankton concentrationsa t 7 C .

rooo8 0 0

600

400

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The delayed feeding study at 7 C revealed that thecriterion of 507o of a sample of larvae initiatingfeeding after deprivation is not valid for establishinga point of no return for haddock and that preyconcentration directly affects the ability of thelarvae to initiate feeding. As far as is known resultslike these have not been demonstrated before withother species and show that the point of no returnmay be flexible. Ability to feed after deprivationdepends on several other factors including species,initial egg size or yolk reserve, and temperature.The point after which larvae are living but unableto feed successfully has been reported to vary fromas few as 4 days for bluegill lawae (Lepomis macro-chirus) at 23.5 C (Toetz 1966) to 36 days at 3-4 Cfor cisco (Leucichthys artedii, John and l{asler 1956)with many intermediate values (Blaxter 1970).Some researchers have considered delayed feedingability as a critical factor in relation to larval survival.Toetz (1966) deflned the so-called "critical period"of larval survival as being from feeding initiationto the point of no return.

This laboratory research implies that haddocklarvae do have a critical period in which mortalitymay be great, that it is a relatively short time duringthe first weeks after hatching, and that it is con-trolled to a certain degree by the critical timing oflarvae encountering planktonic prey in sufficientnumbers so that successful feeding is promoted.

Acknowledgments -I wish to acknowledge Dr D.Au, Mr J. B. Colton Jr., Mr R. C. Hennemuth, andMr R. R. Marak for their critical review of the manu-script. Thanks also go to Mr T. Halavik and Mr A.Smigielski for their technical heip, to Ms M. Marshwho drafted the figures, and to Mr Hennemuth andDr E. Heyerdahl who aided in the calculation of theunbiased mortality coefficients.

Braxtnn, J. H. S. 1,965. The feeding of herringlarvae and their ecology in relation to feeding.Calif. Coop. Oceanic Fish. Invest. Vol. X: 79-88.

1970. Development: eggs and larvae, p. 178-241. /n W. S. Hoar and D. J. Randall [ed.] Fishphysiology. Vol. II. Academic Press, Inc., NewYork, N.Y.

Boconov, V. G. 1939. Characteristics of seasonalappearances in the plankton of polar seas and theirsignificances for forecasts of ice [Osobennostisezonnykh yavlennii v planktone polyarnykh moreii ikh z nachenie dlya ledovykh prognozovl. Zool.Zh. Yol. l8(s): 17-32.

l419

Cor-rox, J. B. Jn. 1965. The distribution andbehavior of pelagic and early demersal stages ofhaddock in relation to sampling techniques. Int.Comm. Northwest Atl. Fish. Spec. Publ. No. 6:J I / - J J J .

JonN, K. R., aNo A. D. Hasr,En. 1956, Observationson some factors affecting the hatching of eggs andthe survival of young shallow-water cisco, Leu-chichthys artedi. Le Sueur, in Lake Mendota,Wisconsin. Limnol. Oceanogr. l: 176-1'94.

LrsrvNnNro, L. N. 1961. Flankton and feeding oflarvae of the Baltic herring in the Riga Gulf. Tr.Nauchno-Issled. Inst. Ryb. Khas. Latvian SSR 3:105-1 38.

Manar, R. R. 1960. Food habits of larval cod,haddock, and coalfish in the Gulf of Maine andGeorges Bank area. J. Cons. Int. Explor. Mer25: 147-157.

O'CoNNrn, C. P., aNo L. P. R.nvrrloNo. 1970. Theeffect of food density on survival and growth ofearly post yolk-sac larvae of the northern anchovyEngraulis mordax Girard) in the laboratory. J.Exp. Mar. Biol. Ecol. 5:187-197.

Ocrr-vrr, H. S. 1938. The food of post larval had-dock with reference to the annual fluctuations inthe haddock broods. Rapp. P-V Reun. Cons.Perm. Int. Explor. Mer. 107(3): 57-66.

Pannrsu, B. B. 1950. Brood fluctuations in theNorth Sea haddock population. Challenger Soc,Abstr. 3(2): 18.

PAvoLvsKAyA, R. M. 1961. La survie des larves deI'anchois de la Mer Noire en fonction de leur ali-mentation. Rapp. Comm. Int. Mer Medit. XVI:345-350.

S.a.rsrN.l, V. P., aNo E. D. Houon. 1972. Effect offood level on the growth and survival of laboratory-reared larvae of bay anchovy (Anchoa mitchilliValenciennes) and scaled sardine (Harengula pensa-colae Goode and Bean). J. Exp. Mar. Biol. Ecol.8: 249-258.

Savrr,rp, A. 1956. Eggs and larvae of haddock(Gadus aeglefinus L.) at Faroe. Mar. Res. 1956(4):I a 1

Srpnr-, R. G. D., aNo J. H. Tonnm. 1960. Principlesand procedures of statistics. McGraw-Hill BookCo., Inc., New York, N.Y. 481 p.

Svsorva, T. K., lNo A. A. Drcrsnvr.. 1965. Therelation between the feeding of cod larvae and pelagicfry and the distribution and abundance of theirprinciple food organisms. Int. Comm. NorthwestAtl . Fish. Spec. Publ. No. 6: 411-416.

Tonrz, D. W. 1966. The changes from endogenousto exogenous sources of energy in bluegill sunfishlarvae. Invest. Indiana Lakes Streams 7 (4) : 115-146.

War,rono, L. A. 1938. Effects of currents on distri-bution and survival of the eggs and larvae of thehaddock (Melanogrammus aeglefinus) on GeorgesBank. Bull. U.S. Bur. Fish. 49QD: 1-73.

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