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Post-harvest seasonal quality of selected molluscan broodstock Pacific oysters (Crassostrea gigas) raised in Alaska and Washington

Stuart R Thomas*1, Ray RaLonde2, Chris Langdon3 & Alexandra Oliveira1

1University of Alaska Fairbanks, School of Fisheries and Ocean Sciences. Fishery Industrial Technology Center Kodiak 2Ray RaLonde - University of Alaska Anchorage

3Dr. Chris Langdon - Professor, Oregon State University,1Dr. Alexandra Oliveira - Associate Professor, University of Alaska Fairbanks

*Presenting Author – University of Alaska Graduate Student

The Alaskan oyster farming industry has shown significant growth in recent years, with a 6-fold increase from 1990-2005, valued at over $566,000 in 2005. However farm gate value of Alaskan oyster has shown an overall decline in marketable oyster production in recent years to a sales value of $441,781 based on figures from 2009 (Latest data: Alaska Department of Fish & Game 2011). The primary objective of this project was to evaluate the biochemical properties, physical and reproductive condition of selected Pacific oysters (Crassostrea gigas) from the USDA-funded Molluscan Broodstock Program (MBP) planted in either Alaska (Kachemak Bay [KB]: Latitude: 59.64oN) or Washington State (Thorndyke Bay [TB]: Latitude: 47.80oN). MBP selects oyster broodstock that results in higher yields, faster growth, and better survival of progeny. To date substantial increases in yields and reduced variability in growth of oysters within families has been achieved, characteristics that could benefit Alaska’s oyster Growers. . A seasonal comparison was also used to determined the effect of overwintering in the two very different environments, upon the intrinsic quality parameters mentioned above, of the MBP oysters. The data will be used to describe the quality of live oysters for the half-shell market.

Kachemak Bay, AK benefits from pristine, unpolluted waters, with high and sustained summer productivity. Here oysters are farmed using lantern nets (figure 1), suspended at controlled heights in the water column. In contrast at Thorndyke Bay, in the similarly productive Puget sound (WA), oysters are grown on trays in the intertidal zone (figure 2). Although the two sites share many oceanographic similarities, there a significant climatic differences between them, in particular with regards to temperature and its effect on feeding, metabolism, growth and reproductive biology of the Pacific oyster.

Selected families of oysters were planted at both sites in 2006 Families observed to have unique and desirable quality attributes identified as important to consumers (Harrington, 2005) will enable the MBP to improve identification criteria to help determine Pacific oyster broodstock best suited for optimal production and grow-out by the Alaskan oyster industry. The top performing MBP families identified at Kachemak Bay have some distinguishing characteristics which may warrant their inclusion when establishing pedigreed lines to serve as the foundation of a long-term breeding program in Alaska.

Replicates of MBP families of oysters grown sub-tidally at KB ended the growout period with significantly lower values than those grown inter-tidally at TB (ANOVA: p < 0.05) in terms of mean yields (KB: 691.52 ± 235.70 g rep-1 vs. TB: 5318.13 ± 1434.42 g rep-1; Fig 3), survival (KB: 39.23 ± 0.98 % vs. TB: 49.48 ± 0.23 %;), and sizes (KB: majority Smalls vs. TB: majority Large; Fig 4). The oyster dry meat condition index [CIHN] developed by Hand & Nell (1999) indicated that the majority oysters at both KB and TB were in “Excellent condition” (Table 3). Dry meat condition index correlated with per cent solid composition (Fig 6) and protein composition (Fig 7). At KB per cent solid decreased significantly between October 2009 (16.59 ± 0.54 %; Fig 7) and June 2010 (13.88 ± 1.26 %; Fig 7); at TB the opposite was true in terms of solids between October (15.42 ± 0.55 %; Fig 7) and June (19.23 ± 0.85 %; Fig 7). At KB per cent protein decreased significantly between October 2009 (50.07 ± 1.65 % w/s; Fig 7) and June 2010 (42.59 ± 1.90 % w/s; Fig 7), and at TB the opposite was true in terms of protein between October (51.52 ± 2.74 % w/s; Fig 7) and June (58.82 ± 1.44 % w/s; Fig 7). Observed changes in protein levels correlated exactly with significant seasonal changes in CIHN (KB Oct 2009 > June 2010: 153.49 ± 13.30 vs. 129.16 ± 7.68 respectively; KB Oct 2009 < KB June 2010: 149.15 ± 9.96 vs. 181.46 ± 8.34 respectively; Fig 7). Glycogen levels were significantly higher (ANOVA: p < 0.05) at KB than at TB in both Oct 2009 (27.01 ± 1.37 % w/s vs. 24.50 ± 1.97 % w/s; Fig 7) and June 2010 (34.64 ± 2.55 % w/s vs. 22.67 ± 1.35 % w/s; Fig 7). MBP oysters grown at KB have reached significantly lower (ANOVA: p < 0.05) levels of apparent reproductive development when compared to those grown at TB, based on per cent gonad area occupying the entire cross-sectional area of whole visceral mass in both Oct 2009 (40.20 ± 13.78 % vs 43.53 ± 18.89 %; Fig 5) and June 2010 (34.63 ± 10.33% vs. 46.74 ± 8.95 %; Fig 5). In June 2010 Oyster grown at KB show significantly lower (ANOVA: p < 0.05) levels of SFA and MUFA than those at TB, and significantly greater levels of beneficial PUFAs, particularly omega-3 (See Fig 8 for values).

In October 2009 and June 2010, a total of 288 oysters from each site from the top seven yielding MBP families and one non-select control group were collected from KB and TB (Table 1). Biometric data were collected and condition indexes calculated for each family. Compositional analyses were performed to determine moisture, protein, glycogen, lipids, ash content (% w/w), and Fatty Acid composition. Reproductive condition was determined by estimating area of visceral mass occupied by gonad. Data were compared and statistically analyzed for differences using ANOVA, taking into consideration the interactions between genetics, latitude, and location.

Hand RE. Nell JA. 1999. Studies on triploid oysters in Australia. XII. Gonad discoloration and meat condition of diploid and triploid Sydney rock oysters ( Saccostrea commercialis) in five estuaries in New South Wales, Australia. Aquaculture 171:181-194.

Harrington E. 2005. Assessment of the oyster market distribution chain and its implications for cooperative formation in the Alaska mariculture industry. [M.Sc. Thesis]. Fairbanks, AK: Univ. Alaska Fairbanks: 85 p. Available from Univ. of Alaska Fairbanks Library.

Imai T. Sakai S. 1961. Study on breeding of Japanese oyster, Crassostrea gigas. Tohoku Journal of Agricultural Research. 12:125-171.Mann R. 1979. Some biochemical and physiological aspects of growth and gametogenesis in Crassostrea gigas and Ostrea edilus grown at sustained elevated temperatures. Journal of the Marine Biological

Association of the U.K. 59:95-110.Steele S. Mulcahy MF. 1999. Gametogenesis of the oyster Crassostrea gigas in southern Ireland. Journal of the Marine Biological Association. 79: 673-686.

RaLonde R. Painter R. 1993. Alaska oyster: Maintaining quality from harvest to halfshell. A quality assurance manual for Alaska oyster growers. Alaskan Shellfish Growers Association. Pp. 5

MBP families designed for success in conditions found at lower latitudes of WA, do not necessarily perform as well in Alaskan waters in terms of growth and survival. As such we identify the need for the Alaskan oyster industry to develop a unique and tailored oyster broodstock and hatchery program. Oysters exhibit reduced feeding, metabolic and growth rates at depressed temperatures. Decreased solids ,protein levels, and associated reductions in CIHN suggest starvation is occuring amongst oysters overwintering sub-itidally in the colder KB, AK when compared to the generally warmer inter-tidal site at TB, WA in the central Puget Sound. Another interesting relationship was observed with regards differences in temperature regimes between the two sites and storage of glycogen over the winter. It appeared that MBP oysters that were thought to be starving over the cold Alaskan winter had adapted a mechanism to store greater levels of glycogen than their counterparts from Washington. This conservation of resources is linked to the oysters inability to reproduce in the colder (<20OC) waters of Alaska (Mann 1979 Steele and Mulcahy, 1999). The adaptation appears to show that oysters in Alaska are metabolizing protein (in the form of muscle) in place of glycogen as an energetic resource over the winter. However gametogenesis begins as waters warm at ~12.5OC, a process which uncompromisingly requires glycogen as a metabolic resource, and we do observe associated partial gametogenesis at both KB and WA. AK oysters benefit from unique nutritional circumstances and cold-water adaptation and as a result are higher in beneficial ω-3 lipids, particularly the marine sourced and reputedly healthy fatty acid DHA (22:6 ω-3) The benefit to consumers of AK oysters is a sweeter tasting oyster, high in healthy omega-3 FAs, in generally excellent condition which farmers are able to provide year round.

This portion of the project presents three hypotheses:

1. There will be significant differences in post harvest product quality between top 7 yielding families

2. Families that have gone through selection for increased yield will differ in post-harvest product quality when compared to non-selected control families?

3. There will be differences in post-harvest product quality as a result of interactions between family and environment?

4. There will be differences in post-harvest product quality between October 2009 and June 2010

INTRODUCTION HYPOTHESES MATERIALS AND METHODS

RESULTS

DISCUSSION

REFERENCES

Total # Oysters Total # Families Oysters/ Family

Physical Analysis

Biochemical Analysis

Reproductive Condition

288 7 + Control 36 12 (n=12) 12 (n=3) 12 (n=3)

Figure 1. Sub-tidal lantern

net culture AKFigure 2. Intertidal Tray

culture WA

Table 1. Breakdown of oyster numbers per family and per analysis per sampling

Acknowledgements: Alaska SeaGrant (NOAA); Evan Durland & Ford Evans (Molluscan Broodstock Program and Oregon State University); Kathryn Brenner, Naim Montazeri, Melanie Chombeau, Trina Lapis, Vanessa Ribeiro,

Huseyin Biceroglu, Kristina Miller, Ralph Elston – The University of Alaska Fairbanks, FITC, Kodiak;

Oyster Growout StudyAugust 2006 to October 2009

Oyster Biometrics Oyster Condition Indices

Oyster Biochemical composition

Oyster Reproductive Condition**

Growth (grams)Survival (Per cent)

Length (mm)Width (mm)

Cup depth (mm)Cavity VolumeLive weight (g)

Meat weight (g)Shell weight (g)

Dry meat IndexEconomic Size IndexWidth: Length RatioCup Depth: Length

Ratio

Moisture (%)Solids (%)

Ash (% w/s)*Protein (% w/s)

Glycogen (% w/s) Lipids (% w/s)

Gut area (%)Gonad area (%)

• % w/s = per cent of solid component** % = per cent of tissue occupying cross section of visceral mass, determined using image analysis software

Table 2. List of recorded data, analyses and post harvest parameters of interest among MBP oysters in this study

0 10 20 30 40 50 60 70 800.00

1000.00

2000.00

3000.00

4000.00

5000.00

6000.00

7000.00

8000.00

K20

K21 K34

K28K24

K44

K46

K0

T20

T21T24 T28

T34

T44

T46

T0

R² = 0.974859550014708

TB (WA)Lin-ear (TB (WA))KB (AK)Lin-ear (KB (AK))

Per cent survival (%) from initial plant out

Mea

n f

amil

y yi

eld

(g

rep

lica

te-1

)

R2 = 0.0749

Runts

0 - 50

.8

Extra S

mall 50

.8 -7

6.2

Small

76

.2 - 1

01.6

Med

ium 10

1.6 -

127.0

Large 1

27.0

≤0

10

20

30

40

50

60

70

Kachemak Bay - Oc-tober 2009

Thorndyke Bay - Oc-tober 2009

Size range (mm)

Pro

por

tion

of

oyst

ers

(%)

Category

Kachemak Bay (AK)October

2009

Thorndyke Bay (WA)October

2009

Kachemak Bay (AK)

June 2010

Thorndyke Bay (WA)

June 2010

  % % % %

CIHN < 60 - Poor condition 

1.04 0.00 3.42 0.00

CIHN 60-80 - Average condition 3.13 0.00 5.13 3.13

CIHN 80-100 - Good condition 7.29 0.00 12.82 2.08

CIHN > 100 - Excellent condition 87.50 100.00 78.63 94.79

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

100.00

Unidentified somatic tissue (%)

Gut area (%)

Gonad area (%)

Location - Season

Per

cen

t (%

)

Ash

Protein

Lipid

Glycogen

KB

(AK

) Oct

09

TB (W

A) O

ct 0

9

KB

(AK

) Jun

e 10

TB (W

A) J

une

10

0

10

20

30

40

50

60

70

Perc

ent w

/s (%

)

Figure 3. Mean percent family survival (August 2006 – October 2009) versus mean family yield (g family-1) of families sampled from KB (AK) and TB (WA)

Figure 4. Distribution of MBP oysters by site within size categories as defined in Painter and RaLonde (1993), for

Alaskan oysters, at the end of the growout period

Figure 5. Per cent area composition (gonad, gut and unidentified somatic tissues) of cross sectional area of whole visceral mass of oyster sections

by sampling location and season

M o is tu re

S o lid s

KB

(AK

) Oct

09

TB (W

A) O

ct 0

9

KB

(AK

) Jun

e 10

TB (W

A) J

une 1

0

1 0

2 0

7 0

8 0

9 0

1 0 0

Perc

ent (

%)

Figure 7. Mean chemical composition (per cent of wet solid weight) of MBP oysters at KB and TB in October 2009 and June 2010 (Whiskers:

Standard deviation)

Figure 6. Mean per cent moisture and solid composition of MBP oysters at KB and TB in October 2009 and June 2010 (Whiskers:

Standard deviation)

Figure 8. Mean composition of key fatty acid groups (per cent of total lipid) of MBP oysters at KB and TB in June 2010 (Whiskers:

Standard deviation)

Table 3. Distribution of MBP oysters by site and sampling time within categories for dry meat condition (CIHN) as defined by Westley (1959), for Alaskan oysters

S F A

M U F A

P U F A

O m ega -3

O m ega -6

K B (A K ) Ju n e 1 0 T B (W A ) Ju n e 1 00

1 0

2 0

3 0

4 0

5 0

6 0

Perc

ent (

% o

f lip

id)