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Growth of sablefish (Anoplopoma fimbria) in marine net-pens
Aquaculture, 36 (1984) 379-386 Elsevier Science Publishers B.V., Amsterdam -Printed
GROWTH OF SABLEFISH NET-PENS
379
in The Netherlands
(ANOPLOPOMA FIMBRIA)IN MARINE
KURT X. GORES and EARL F. PRENTICE Northwest and Alaska Fisheries Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, 2725 Montlake Boulevard East, Seattle, WA 98112 (U.S.A.) (Accepted
12 May 1983)
ABSTRACT Gores, K.X. and Prentice, E.F., 1984. Growth marinenet-pens.Aquaculture, 36: 379-386.
of sablefish (Anoplopoma
fimbria)
in
Sablefish (Anoplopoma fimbria) were reared in 1.6 X 2.0 X 1.2 m deep net-pens for 36 months using low-cost, locally available diets (frozen salmon and herring). Post-capture mortality, wound repair, and adaptability to floating net-pens were investigated. Results showed no mortality directly related to capture and rapid healing of wounds resulting from capture. All fish adapted to captivity without apparent difficulty. For grow-out trials, 36 age l+ fish were tagged for individual identification. Male and female fish were identified using an immunodiffusion technique. Net-pen adaptability studies tested three diets. Maximum observed mean weight gains were 0.10 kg per fish per month. After 2 years, there was no significant difference in growth (length or weight) between any of the diets. A different weight gain was recorded between male and female fish fed the salmon diet.
INTRODUCTION
The present annual U.S. catch of sablefish (Anoplopoma fimbriu), commonly called black-cod, exceeds 3600 metric tons. An additional 180 t are imported. Sablefish are processed in several different ways; the largest percentage of the catch is smoked, followed in order of magnitude by fresh steak and fillets, salted portions, and pickled products (Low et al., 1976). The highest prices paid for sablefish are for fish from 2 to 3 kg or more (dressed weight), because of their increased palatability and the usefulness of larger fillets for smoked, salted, and pickled products. Lower prices are paid for sablefish from 1 to 2 kg, but this size is supplying an increasing demand for steaks and fillets. A lower price is paid for injured fish (cuts, abrasions, etc.). At present, there is no market for sablefish weighing less than 1 kg. In order to augment the present supply of eablefish, large, injured fish or undersize fish might be held in captivity until reaching favorable conditions
0044-8486/84/$03.00
o 1984 Elsevier Science Publishers B.V.
for market. A study was begun in 1977 on the feasibility of rearing sablefish in floating seawater net-pens for this purpose. The study investigated postcapture mortality; wound repair; adaptability to floating net-pens; and subsequently, growth and survival using three low-cost, readily available diets which might be used by a commercial rearing operation. METHODS
AND MATERIALS
Fifty-nine sablefish were captured by bottom trawling in Puget Sound near Port Susan, WA. All fish were about l-year old. Mean length and weight were 288 mm and 228 g, respectively. The fish were transferred to the Northwest and Alaska Fisheries Center’s Manchester Marine Experimental Station on Clam Bay (Fig. 1) and divided into four groups. Three groups were held in circular fiberglass tanks (1.2 m in diameter X 0.8 m deep). The fourth group was held in a floating net-pen (1.6 X 2.0 X 1.2 m deep). All groups were fed frozen Pacific herring (Clupea harengus pallasi) and/or juvenile salmon (Oncorhynchus spp,) which had not survived culture at the station. Post capture, wound repair, and adaptability to floating net-pens were monitored. After 6 months, all remaining fish (n=39) were redistributed equally into three net-pens and a serially-numbered Monel strap tag was attached to the operculum of each fish. Individual growth rate and survival with three, lowcost, easily available diets were monitored for 2 years. Although the natural diet of sablefish changes seasonally and even daily depending on food availability (Low et al., 1976), the sablefish in each net-pen were maintained on one of three fixed diets: (1 j frozen juvenile salmon from a local commercial salmon producer, (2) frozen herring from a nearby bait supplier, or (3) an alternating (mixed) diet of salmon on one day and herring the next day. The sablefish were fed once daily, 5 days a week. Salmon and herring >lO cm in length were chopped into 2 to 4 cm pieces before feeding. Smaller salmon and herring were fed whole. Food was weighed before feeding; uneaten food was removed and weighed each day to allow calculation of gross food conversion. Rations were adjusted so that nearly all food was consumed daily. Water absorption contributed significantly to the weight of the uneaten food. Water absorption curves were established for frozen herring and salmon to adjust the weight of the uneaten portion. Before removal of uneaten food, each pen was inspected for mortalities. The fish were anesthetized with MS-222 (tricaine methanesulfonate), weighed to the nearest 5 g, and measured (fork length) to the nearest millimeter at 30- to 60day intervals. The concentration of MS-222 was not calculated. However, as noted by Kennedy (1969), sablefish are able to withstand more than ten times the concentration of MS-222 fatal to salmon. Seasurface temperature and salinity were recorded daily and ranged from 6.2 to 13.O”C (Fig. 2) and 24.0 to 32.0°/,,0. Net-pens were changed at 5- to g-month intervals depending on the amount of biofouling. A nondestructuve serological test was performed to identify females in
Strait of Juan de
15 Nautical
miles
Fig. 1. Location of Northwest and Alaska Fisheries Center’s Manchester Marine Experimental Station on Clam Bay.
382
Fig. 2. Surface seawater temperature
at Clam Bay.
each group, as described by Utter and Ridgway (1965). The test detects the presence or absence of a serum vitellin component (HM factor) by an immunodiffusion technique. A positive result of the test indicates a female (capable of synthesizing vitellin); a negative result indicates either a male or female not capable of synthesizing vitellin. Scale samples were removed from each fish to determine age. Scales were removed individually from the left side midway between the first dorsal fin and lateral line, and read using standard methods. The effects of the three test diets on weight and length gain were analyzed using predictive samples reuse, described by Geisser and Eddy (1979). Males and females were analyzed separately. For both weight and length gain data, five models, M,, . . ., M,, were formulated: MI assertsthat all three diets are the same for weight gain or length gain; M, asserts that the salmon and herring diets are the same but differ from the alternating diet; M3 asserts that the herring and alternating diets are the same, but the salmon diet differs from them; M, asserts that the herring diet differs from the salmon and alternating diets, but the latter two are the same; and M, asserts that all three diets differ. The data were used to select one of the five possible models. The criterion used was the low structure selection criterion described in Section 3 of Geisser and Eddy (1979). The set of covariates 2, in their notation, consisted of indicator variables specifying population sampled and date. Four cases (weight gain for females, weight gain for males, length gain for females, and length gain for males) were considered. The same analysis was used to compare males and females for a given diet. Here, there are only two possible models, M, and M,, where M, asserts that males and females do not differ, and M, asserts that they do differ for weight gain or length gain. RESULTS
AND DISCUSSIONS
There were no short-term mortalities related to capture, even though 90% of the fish exhibited fin hemorrhaging. After 3 months only 1% of the fish
383
continued to show signs of hemorrhaging. Initial mortalities included 16 fish from low-dissolved oxygen during a water pump failure, one fish from furunculosis (Aeromonas sulmonicida), and three fish from unknown causes. After redistribution of the fish into net-pens, survival was 82.0% for the a-year grow-out period. Mortalities were attributed to Vibrio anguilhrum in two fish; furunculosis in one fish; and four fish lost to river otter (Lutra cunudensis) predation. The fish suffered no physical or environmental stress which allowed furunculosis or other disease to reach epizootic levels as seen by Kennedy and Smith (1972). The wound from the opercular tag healed after 1 month. In many cases, tissue growing over the tag had to be removed to read the tag number each month. Kennedy (1969) reported rapid healing of scalpel slashes cut into the musculature to identify individual fish. Tag loss was high, and approximately 50% of the fish had to be retagged at least once during the study. The fish had no difficulty adapting to confinement in the net-pens. However, lesions at the base of the pectoral fins, on the operculum, and/or on the anal fin periodically appeared without apparent cause. These lesions (5 to 8 mm in diameter), at times affecting nearly 40% of the test group, remained 1 to 7 months (mean 2 months) with the greatest incidence from September through December. Lesions appeared with similar frequency on fish receiving all three diets. Attempts were made to culture pathogenic bacteria from lesions on tripticase soy agar (TSA) without success. Snout abrasions also occurred, presumably from contact with the net-pen. Both the lesions and snout abrasions are visual blemishes which could affect marketability. The occurrence of these blemishes, however, may be reduced by rearing the fish in larger net-pens. Approximately 38% of the fish became blind in at least one eye from abrasion by the net-pen, nutritional deficiency, or other unknown factors. Several fish developed severe eye infection causing the eyes to protrude. Similar eye problems were seen by Kennedy (1969). This may also affect marketability. Based on size at capture and scale analyses, all fish were in the same ageclass. At the start of the grow-out trials, all the fish were age l+. Natural mortality occurs at about 5 to 7 years, with males maturing earlier (5+) than females (Low et al., 1976). The presumed spawning period in nature is from late January to early March (Kennedy and Fletcher, 1968). In this study, however, a single mature male (age 2+) from the herring diet test group was observed. Milt was easily pressed from the fish. The same male ripened again the next year and remained ripe for 4 months (late February to late May). A second male at age 3+ remained ripe for 3 months (late February to late April). No ripe females were observed during the study. The sablefish in all test groups consumed widely varying amounts of food. Often a substantial portion of the daily food ration would not be consumed for consecutive days, then feeding would resume and the total ration would
384 4000
-
3800
-
3600
-
3400
-
3200
-
3000
-
2800
-
2000
-
Herting Salmon
-.-.-
Alternating
~herringidnonl
DJFMAMJJASONDJFMAMJJASOND 1978 I+
1979
1980 TIME
Fig. 3. Growth of sablefiih reared in seawater net-pens and fed one of three test diets.
be consumed daily. During several measurement periods, little if any growth was seen which corresponded to periods of sporadic feeding (Fig. 3). This variation may be due to changes in water temperature, maturation, or diet quality. Long term diet evaluation tests were conducted for the grow-out trials in net-pens. The predictive sample reuse criterion of Geisser and Eddy (1979) selected M, as the most appropriate model for all four cases considered. There was no significant difference in fish length or weight between any of the diet lots. In the comparison between males and females for a given diet, the only case where M, was selected by computer analysis as the most appropriate of the two models was for weight-gain difference between males and females on the salmon diet. It should be noted, however, that the mean size and growth rate of males was always lower (even through not statistically different) than females within any diet group (Table I), Pruter (1954) reported that female sablefish were larger than males from age 3+ to 8+ in nature. A size difference was noted at the time of capture (age l+), but this could be related to the small sample size or to the specific population sampled. Pruter (1954) also reported a lack of differential growth between sexes for wild fish less than age 2+. These data showed a trend towards differential growth that would probably have become statistically significant in all cases had the study continued. The growth rate of fish within any of the three diet groups exceeded that reported by Pruter (1954) for fish in the wild (0.04 kg/month). The mean overall growth (length and weight) after 25 months of culture was: 3.1 mm per fish per month and 0.10 kg per fish per month for fish fed the herring diet, 3.0 mm per fish per month and 0.08 kg per fish per month for fish fed
385 TABLE
I
Growth
of sablefish in relation
Diet
Sex
Herring M F Salmon M F Mixed M F aDataonly
na
Mean starting
Mean ending
Weight CB)
Length (mm)
Wei&t (9)
Length (mm)
Weight (kg per fish per month)
Length (mm per fti per month)
496.6 495.4 419.3 500.1 474.8 497.3
3122.5 4266.0 2046.7 3650.0 2915.0 3955.7
661.6 677.2 681.7 674.4 623.8 677.7
0.07 0.12 0.05 0.09 0.07 0.11
6.23 1.27 6.50 6.97 6.96 7.22
__ 1357.5 1312.0 766.7 1375;o 1138.8 1319.3
4 5 3 9 4 7
for those
to sex and diet Mean growth
rate
fish which could be individuallyidentified throughout the study.
TABLE II Growth rates of sablefish in relation to period of culture, seawater temperature, and diet Seawater temperature
Period
Above 10°C
11-17-78 to 12-20-78
Below 10°C
Diet
Growth rate Weight (kg per fiih per month)
Length (kg per fish per month)
Herring Salmon Mixed
0.20 0.19 0.21
23.5 23.5 20.9
04-20-79 to 12-17-79
Herring Salmon Mixed
0.11 0.08 0.07
7.4 7.8 4.8
04-22-80 to 12-04-80
Herring Salmon Mixed
0.07 0.05 0.07
2.7 2.4 2.9
12-20-78 to 04-20-79
Herring Salmon Mixed
0.12 0.11 0.14
10.4 10.4 13.0
12-17-79 to 04-22-79
Herring Salmon Mixed
0.09 0.08 0.11
8.0 6.3 8.6
the salmon diet, and 2.7 mm fish per month and 0.09 kg per fish per month for fish fed the mixed diet. Kennedy and Smith (1972) reported growth rate8 up to 0.25 kg per fish per month for fish reared for 14 months under similar conditions. A relationship between growth rate and seawater temperature was reported by Kennedy (1972) and Kennedy and Smith (1972) for sablefish reared in tanks and net-pens. A reduced growth was reported for fish weighing > 1.8 kg when seawater temperatures were >lO” C during May to September. These result8 were not supported by this work (Table II). The growth rate
366
appeared to be more closely related to fish age, length of culture, and diet rather than water temperature. These factors are thought to have masked the effect of water temperature on the growth of our fish. In conclusion, the sablefish are well suited for culture in many respects, but their growth rate may preclude commercial production because of labor, facility, and food costs. The growth achieved in this study exceeded growth in nature; however, this is insufficient reason to make long-term holding to full market size practical at this time. From biological and technical viewpoints, large fish, especially females could be held in captivity to allow wound repair or to take advantage of off-season price changes. Site selection for such practices would be critical for the economic success of the operation. REFERENCES Geisser, S. and Eddy, W.F., 1979. A predictive approach to model selection. J. Am. Stat. Assoc., 74: 153-160. Kennedy, W.A., 1969. Sablefish culture - a preliminary report. Fish. Res. Board Can. Tech. Rep., 107 : l-20. Kennedy, W.A., 1972. Preliminary study of sablefish culture, a potential new industry. J. Fish. Res. Board Can., 29: 207-210. Kennedy, W.A. and Fletcher, F.T., 1968. The 1964-1965 sablefish study. Fish. Res. Board Can. Tech. Rep., 74: l-24. Kennedy, W.A. and Smith, M.S., 1972. Sablefish culture - progress in 1971. Fish. Res. Board Can. Tech. Rep., 309: l-17. Low, L.L., Tanonaka, G.K. and Shippen, H.H., 1976. Sablefish of the Northeastern Pacific Ocean and Bering Sea. Natl. Mar. Fish. Serv., Northwest and Alaska Fish. Cent., Seattle, WA, Processed Rep., 115 pp. Pruter, A.T., 1954. Age and growth of the Oregon sablefish, Anoplopoma fimbria. Pac. Mar. Fish. Comm. Bull., 3: 122-128. Utter, F.M. and Ridgway, G.J., 1965. A serologically detected serum factor associated with maturity in English sole, Parophrys vetulus, and Pacific halibut, Hippoglossus stenolepis. Fish. Bull., U.S., 66: 47-58.
GROWTH OF SABLEFISH NET-PENS
379
in The Netherlands
(ANOPLOPOMA FIMBRIA)IN MARINE
KURT X. GORES and EARL F. PRENTICE Northwest and Alaska Fisheries Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, 2725 Montlake Boulevard East, Seattle, WA 98112 (U.S.A.) (Accepted
12 May 1983)
ABSTRACT Gores, K.X. and Prentice, E.F., 1984. Growth marinenet-pens.Aquaculture, 36: 379-386.
of sablefish (Anoplopoma
fimbria)
in
Sablefish (Anoplopoma fimbria) were reared in 1.6 X 2.0 X 1.2 m deep net-pens for 36 months using low-cost, locally available diets (frozen salmon and herring). Post-capture mortality, wound repair, and adaptability to floating net-pens were investigated. Results showed no mortality directly related to capture and rapid healing of wounds resulting from capture. All fish adapted to captivity without apparent difficulty. For grow-out trials, 36 age l+ fish were tagged for individual identification. Male and female fish were identified using an immunodiffusion technique. Net-pen adaptability studies tested three diets. Maximum observed mean weight gains were 0.10 kg per fish per month. After 2 years, there was no significant difference in growth (length or weight) between any of the diets. A different weight gain was recorded between male and female fish fed the salmon diet.
INTRODUCTION
The present annual U.S. catch of sablefish (Anoplopoma fimbriu), commonly called black-cod, exceeds 3600 metric tons. An additional 180 t are imported. Sablefish are processed in several different ways; the largest percentage of the catch is smoked, followed in order of magnitude by fresh steak and fillets, salted portions, and pickled products (Low et al., 1976). The highest prices paid for sablefish are for fish from 2 to 3 kg or more (dressed weight), because of their increased palatability and the usefulness of larger fillets for smoked, salted, and pickled products. Lower prices are paid for sablefish from 1 to 2 kg, but this size is supplying an increasing demand for steaks and fillets. A lower price is paid for injured fish (cuts, abrasions, etc.). At present, there is no market for sablefish weighing less than 1 kg. In order to augment the present supply of eablefish, large, injured fish or undersize fish might be held in captivity until reaching favorable conditions
0044-8486/84/$03.00
o 1984 Elsevier Science Publishers B.V.
for market. A study was begun in 1977 on the feasibility of rearing sablefish in floating seawater net-pens for this purpose. The study investigated postcapture mortality; wound repair; adaptability to floating net-pens; and subsequently, growth and survival using three low-cost, readily available diets which might be used by a commercial rearing operation. METHODS
AND MATERIALS
Fifty-nine sablefish were captured by bottom trawling in Puget Sound near Port Susan, WA. All fish were about l-year old. Mean length and weight were 288 mm and 228 g, respectively. The fish were transferred to the Northwest and Alaska Fisheries Center’s Manchester Marine Experimental Station on Clam Bay (Fig. 1) and divided into four groups. Three groups were held in circular fiberglass tanks (1.2 m in diameter X 0.8 m deep). The fourth group was held in a floating net-pen (1.6 X 2.0 X 1.2 m deep). All groups were fed frozen Pacific herring (Clupea harengus pallasi) and/or juvenile salmon (Oncorhynchus spp,) which had not survived culture at the station. Post capture, wound repair, and adaptability to floating net-pens were monitored. After 6 months, all remaining fish (n=39) were redistributed equally into three net-pens and a serially-numbered Monel strap tag was attached to the operculum of each fish. Individual growth rate and survival with three, lowcost, easily available diets were monitored for 2 years. Although the natural diet of sablefish changes seasonally and even daily depending on food availability (Low et al., 1976), the sablefish in each net-pen were maintained on one of three fixed diets: (1 j frozen juvenile salmon from a local commercial salmon producer, (2) frozen herring from a nearby bait supplier, or (3) an alternating (mixed) diet of salmon on one day and herring the next day. The sablefish were fed once daily, 5 days a week. Salmon and herring >lO cm in length were chopped into 2 to 4 cm pieces before feeding. Smaller salmon and herring were fed whole. Food was weighed before feeding; uneaten food was removed and weighed each day to allow calculation of gross food conversion. Rations were adjusted so that nearly all food was consumed daily. Water absorption contributed significantly to the weight of the uneaten food. Water absorption curves were established for frozen herring and salmon to adjust the weight of the uneaten portion. Before removal of uneaten food, each pen was inspected for mortalities. The fish were anesthetized with MS-222 (tricaine methanesulfonate), weighed to the nearest 5 g, and measured (fork length) to the nearest millimeter at 30- to 60day intervals. The concentration of MS-222 was not calculated. However, as noted by Kennedy (1969), sablefish are able to withstand more than ten times the concentration of MS-222 fatal to salmon. Seasurface temperature and salinity were recorded daily and ranged from 6.2 to 13.O”C (Fig. 2) and 24.0 to 32.0°/,,0. Net-pens were changed at 5- to g-month intervals depending on the amount of biofouling. A nondestructuve serological test was performed to identify females in
Strait of Juan de
15 Nautical
miles
Fig. 1. Location of Northwest and Alaska Fisheries Center’s Manchester Marine Experimental Station on Clam Bay.
382
Fig. 2. Surface seawater temperature
at Clam Bay.
each group, as described by Utter and Ridgway (1965). The test detects the presence or absence of a serum vitellin component (HM factor) by an immunodiffusion technique. A positive result of the test indicates a female (capable of synthesizing vitellin); a negative result indicates either a male or female not capable of synthesizing vitellin. Scale samples were removed from each fish to determine age. Scales were removed individually from the left side midway between the first dorsal fin and lateral line, and read using standard methods. The effects of the three test diets on weight and length gain were analyzed using predictive samples reuse, described by Geisser and Eddy (1979). Males and females were analyzed separately. For both weight and length gain data, five models, M,, . . ., M,, were formulated: MI assertsthat all three diets are the same for weight gain or length gain; M, asserts that the salmon and herring diets are the same but differ from the alternating diet; M3 asserts that the herring and alternating diets are the same, but the salmon diet differs from them; M, asserts that the herring diet differs from the salmon and alternating diets, but the latter two are the same; and M, asserts that all three diets differ. The data were used to select one of the five possible models. The criterion used was the low structure selection criterion described in Section 3 of Geisser and Eddy (1979). The set of covariates 2, in their notation, consisted of indicator variables specifying population sampled and date. Four cases (weight gain for females, weight gain for males, length gain for females, and length gain for males) were considered. The same analysis was used to compare males and females for a given diet. Here, there are only two possible models, M, and M,, where M, asserts that males and females do not differ, and M, asserts that they do differ for weight gain or length gain. RESULTS
AND DISCUSSIONS
There were no short-term mortalities related to capture, even though 90% of the fish exhibited fin hemorrhaging. After 3 months only 1% of the fish
383
continued to show signs of hemorrhaging. Initial mortalities included 16 fish from low-dissolved oxygen during a water pump failure, one fish from furunculosis (Aeromonas sulmonicida), and three fish from unknown causes. After redistribution of the fish into net-pens, survival was 82.0% for the a-year grow-out period. Mortalities were attributed to Vibrio anguilhrum in two fish; furunculosis in one fish; and four fish lost to river otter (Lutra cunudensis) predation. The fish suffered no physical or environmental stress which allowed furunculosis or other disease to reach epizootic levels as seen by Kennedy and Smith (1972). The wound from the opercular tag healed after 1 month. In many cases, tissue growing over the tag had to be removed to read the tag number each month. Kennedy (1969) reported rapid healing of scalpel slashes cut into the musculature to identify individual fish. Tag loss was high, and approximately 50% of the fish had to be retagged at least once during the study. The fish had no difficulty adapting to confinement in the net-pens. However, lesions at the base of the pectoral fins, on the operculum, and/or on the anal fin periodically appeared without apparent cause. These lesions (5 to 8 mm in diameter), at times affecting nearly 40% of the test group, remained 1 to 7 months (mean 2 months) with the greatest incidence from September through December. Lesions appeared with similar frequency on fish receiving all three diets. Attempts were made to culture pathogenic bacteria from lesions on tripticase soy agar (TSA) without success. Snout abrasions also occurred, presumably from contact with the net-pen. Both the lesions and snout abrasions are visual blemishes which could affect marketability. The occurrence of these blemishes, however, may be reduced by rearing the fish in larger net-pens. Approximately 38% of the fish became blind in at least one eye from abrasion by the net-pen, nutritional deficiency, or other unknown factors. Several fish developed severe eye infection causing the eyes to protrude. Similar eye problems were seen by Kennedy (1969). This may also affect marketability. Based on size at capture and scale analyses, all fish were in the same ageclass. At the start of the grow-out trials, all the fish were age l+. Natural mortality occurs at about 5 to 7 years, with males maturing earlier (5+) than females (Low et al., 1976). The presumed spawning period in nature is from late January to early March (Kennedy and Fletcher, 1968). In this study, however, a single mature male (age 2+) from the herring diet test group was observed. Milt was easily pressed from the fish. The same male ripened again the next year and remained ripe for 4 months (late February to late May). A second male at age 3+ remained ripe for 3 months (late February to late April). No ripe females were observed during the study. The sablefish in all test groups consumed widely varying amounts of food. Often a substantial portion of the daily food ration would not be consumed for consecutive days, then feeding would resume and the total ration would
384 4000
-
3800
-
3600
-
3400
-
3200
-
3000
-
2800
-
2000
-
Herting Salmon
-.-.-
Alternating
~herringidnonl
DJFMAMJJASONDJFMAMJJASOND 1978 I+
1979
1980 TIME
Fig. 3. Growth of sablefiih reared in seawater net-pens and fed one of three test diets.
be consumed daily. During several measurement periods, little if any growth was seen which corresponded to periods of sporadic feeding (Fig. 3). This variation may be due to changes in water temperature, maturation, or diet quality. Long term diet evaluation tests were conducted for the grow-out trials in net-pens. The predictive sample reuse criterion of Geisser and Eddy (1979) selected M, as the most appropriate model for all four cases considered. There was no significant difference in fish length or weight between any of the diet lots. In the comparison between males and females for a given diet, the only case where M, was selected by computer analysis as the most appropriate of the two models was for weight-gain difference between males and females on the salmon diet. It should be noted, however, that the mean size and growth rate of males was always lower (even through not statistically different) than females within any diet group (Table I), Pruter (1954) reported that female sablefish were larger than males from age 3+ to 8+ in nature. A size difference was noted at the time of capture (age l+), but this could be related to the small sample size or to the specific population sampled. Pruter (1954) also reported a lack of differential growth between sexes for wild fish less than age 2+. These data showed a trend towards differential growth that would probably have become statistically significant in all cases had the study continued. The growth rate of fish within any of the three diet groups exceeded that reported by Pruter (1954) for fish in the wild (0.04 kg/month). The mean overall growth (length and weight) after 25 months of culture was: 3.1 mm per fish per month and 0.10 kg per fish per month for fish fed the herring diet, 3.0 mm per fish per month and 0.08 kg per fish per month for fish fed
385 TABLE
I
Growth
of sablefish in relation
Diet
Sex
Herring M F Salmon M F Mixed M F aDataonly
na
Mean starting
Mean ending
Weight CB)
Length (mm)
Wei&t (9)
Length (mm)
Weight (kg per fish per month)
Length (mm per fti per month)
496.6 495.4 419.3 500.1 474.8 497.3
3122.5 4266.0 2046.7 3650.0 2915.0 3955.7
661.6 677.2 681.7 674.4 623.8 677.7
0.07 0.12 0.05 0.09 0.07 0.11
6.23 1.27 6.50 6.97 6.96 7.22
__ 1357.5 1312.0 766.7 1375;o 1138.8 1319.3
4 5 3 9 4 7
for those
to sex and diet Mean growth
rate
fish which could be individuallyidentified throughout the study.
TABLE II Growth rates of sablefish in relation to period of culture, seawater temperature, and diet Seawater temperature
Period
Above 10°C
11-17-78 to 12-20-78
Below 10°C
Diet
Growth rate Weight (kg per fiih per month)
Length (kg per fish per month)
Herring Salmon Mixed
0.20 0.19 0.21
23.5 23.5 20.9
04-20-79 to 12-17-79
Herring Salmon Mixed
0.11 0.08 0.07
7.4 7.8 4.8
04-22-80 to 12-04-80
Herring Salmon Mixed
0.07 0.05 0.07
2.7 2.4 2.9
12-20-78 to 04-20-79
Herring Salmon Mixed
0.12 0.11 0.14
10.4 10.4 13.0
12-17-79 to 04-22-79
Herring Salmon Mixed
0.09 0.08 0.11
8.0 6.3 8.6
the salmon diet, and 2.7 mm fish per month and 0.09 kg per fish per month for fish fed the mixed diet. Kennedy and Smith (1972) reported growth rate8 up to 0.25 kg per fish per month for fish reared for 14 months under similar conditions. A relationship between growth rate and seawater temperature was reported by Kennedy (1972) and Kennedy and Smith (1972) for sablefish reared in tanks and net-pens. A reduced growth was reported for fish weighing > 1.8 kg when seawater temperatures were >lO” C during May to September. These result8 were not supported by this work (Table II). The growth rate
366
appeared to be more closely related to fish age, length of culture, and diet rather than water temperature. These factors are thought to have masked the effect of water temperature on the growth of our fish. In conclusion, the sablefish are well suited for culture in many respects, but their growth rate may preclude commercial production because of labor, facility, and food costs. The growth achieved in this study exceeded growth in nature; however, this is insufficient reason to make long-term holding to full market size practical at this time. From biological and technical viewpoints, large fish, especially females could be held in captivity to allow wound repair or to take advantage of off-season price changes. Site selection for such practices would be critical for the economic success of the operation. REFERENCES Geisser, S. and Eddy, W.F., 1979. A predictive approach to model selection. J. Am. Stat. Assoc., 74: 153-160. Kennedy, W.A., 1969. Sablefish culture - a preliminary report. Fish. Res. Board Can. Tech. Rep., 107 : l-20. Kennedy, W.A., 1972. Preliminary study of sablefish culture, a potential new industry. J. Fish. Res. Board Can., 29: 207-210. Kennedy, W.A. and Fletcher, F.T., 1968. The 1964-1965 sablefish study. Fish. Res. Board Can. Tech. Rep., 74: l-24. Kennedy, W.A. and Smith, M.S., 1972. Sablefish culture - progress in 1971. Fish. Res. Board Can. Tech. Rep., 309: l-17. Low, L.L., Tanonaka, G.K. and Shippen, H.H., 1976. Sablefish of the Northeastern Pacific Ocean and Bering Sea. Natl. Mar. Fish. Serv., Northwest and Alaska Fish. Cent., Seattle, WA, Processed Rep., 115 pp. Pruter, A.T., 1954. Age and growth of the Oregon sablefish, Anoplopoma fimbria. Pac. Mar. Fish. Comm. Bull., 3: 122-128. Utter, F.M. and Ridgway, G.J., 1965. A serologically detected serum factor associated with maturity in English sole, Parophrys vetulus, and Pacific halibut, Hippoglossus stenolepis. Fish. Bull., U.S., 66: 47-58.