摘要:

Abstract.Chinook salmon,Oncorhynchus tshawytscha(Walbaum), from a northern streamtype (Bear River) and a southern ocean‐type (Robertson Creek) population in British Columbia were mated within populations in a nested breeding design and the resulting juveniles were challenged with high water temperatures. Juveniles in the southern population died significantly later than those in the northern population, but none of the variation among families in mortality rate or time to death in the southern population was attributable to additive genetic variation. Non‐additive genetic or maternal effects or both were observed for mortality rates in the Robertson Creek population, whereas additive genetic effects were observed for mortality at temperatures less than 22°C in the Bear River population. Larger fish survived better during the challenges than did smaller fish, and there was a negative genetic correlation (based on dam variance components) between body weight and morta

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00502.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.An Aquatector oxygen injection unit was used to supersaturate a hatchery water supply to 200% oxygen saturation (18–20mg/l) and increase the total gas pressure to 120% of saturation. Nitrogen saturation was reduced to near 100%. Rainbow trout,Oncorhynchus mykiss(Walbaum), held in the treated water developed signs of gas bubble disease in 4 days, and 50% died within 20 days. We demonstrated that supersaturated total gas pressure due to excessive oxygen saturation causes gas bubble disease in the absence of supersaturated nitrogen gas. It is recommended that users of oxygen injection systems closely adjust the amount of oxygen added to the water to keep the total gas pressure near saturatio

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00503.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Production of Florida red tilapia seed (eggs, sacfry and fry) in 34‐m2above‐ground tanks using recirculated brackishwater (12 ppt) was studied over a 5‐month period on Lee Stocking Island (Exuma Cays, Bahamas). Four tanks were stocked with year class 1 (YCI) breeders, while 2 tanks were stocked with year class 2 (YCII) breeders at densities of 200 and 240/tank (5·9 and 7·1/m2), respectively, and at a sex ratio of 3 females to 1 male, beginning in November 1988. Seed production was measured by removing free‐swimming fry from tanks and eggs and sacfry from the mouths of brooding females, and assessing the number of each at 15 to 16‐day intervals from February to June 1989. Average seed production (seed/m2/day) was significantly higher in YCI (52·3) than in YCII (36·0) broodstock, indicating the advantages of replacing broodstock with yearling breed

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00504.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Fifty each of F2‐generation gold (gg), bronze (Gg), and black (GG)Oreochromis mossambicus(Peters) and either zero, four or eight largemouth bass,Micropterus salmoides, (Lacepède) were stocked in 20‐m2concrete tanks. After 7 days, water in all tanks was drained, and fish in each tank were censused. Largemouth bass ate 18% of the tilapia in the four‐bass treatment (1 tilapia/bass/day) and 60% of the tilapia in the eight‐bass treatment (1·6 tilapia/bass/day); the difference was significant (P=0–05). In the four‐bass treatment there was a greater observed mean predation rate on gold than that on black or on bronze tilapia, but the difference was not significant: largemouth bass ate 25% of the gold tilapia, 16% of the bronze tilapia, and 13% of the black tilapia. In the eight‐bass treatment, predation on the gold tilapia was significantly greater than that on both bronze (P=0·05) and on black (P=0·06) tilapia; predation on bronze and black tilapia was similar: largemouth bass ate 80% of the gold tilapia, 48% of the bronze tilapia, and 51% of the black tilapia. Overall average total predation (both treatments combined) on gold tilapia was significantly (P=0·06) greater than that on both bronze and on black tilapia, which did not differ: largemouth bass ate 52% of the gold tilapia, 32% of the bronze tilapia, and 32% of the black tilapia. The increased vulnerability of gold tilapia to predation was a negative pleiotropic effec

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00505.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.A feeding experiment was conducted in aquaria to evaluate growth, survival and food consumption by paddlefish, Polyodon spathula (Walbaum), fry fed live Daphnia pulex, brine shrimp nauplii, Artemia sp. (L.), from two different geographical sources, or one of three commercial dry diets. Fry were fed from first feeding (day 8 post‐hatch) to day 17 post‐hatch. All diets had similar percentages of crude protein and lipid. Fatty acid composition was similar in all diets except for Great Salt Lake brine shrimp nauplii which had a higher percentage of linolenic acid, 18:3 (n‐3), and a lower percentage of eicosapentaenoic acid, 20:5 (n‐3). Paddlefish fed live food organisms were significantly (P<0·05) larger than those fed non‐living diets. Survival was significantly higher (P0·05) among treatments. Poorer growth and survival by fish fed prepared diets may have been due to limited digestibility of the dry diets

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00506.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.A 156‐day cage feeding trial was conducted with fingerling seabass,Lates calcarifer(Bloch), and grouper,Epinephelus tauvina(Forskal), so as to test six different dietary feeding regimes, namely no exogenous feeding (NF), frozen fish (FF), commercial shrimp finisher pellet (SP), in‐house prepared dry pellet RDI (RDI) and RD2 (RD2), and an in‐house prepared moist pellet (frozen fish: diet Rd1, 40:60 mixture w/w — code MP). Seabass fed FF and MP displayed the best growth response, with fish (30/m3) growing from an initial weight of 8·9g and 8·5g to a final weight of 285·5g and 257·5 g in 156 days, with a food conversion ratio of 3·77–5·10 (dry matter basis 1·15 – 1·95), and with a survival of 93·3 and 93·3% respectively. Similarly, grouper fed FF and MP also displayed the best growth response, with fish (30/m3) growing from an initial weight of 23·8 g and 25·8g to a final weight of 471·7g and 388·7g in 156 days, with a food conversion ratio of 3·53–4·16 (dry matter basis 0·89–1·06) and 1·73–2·96 (dry matter basis 1·06–1·80), and with a survival of 90 and 98·3% respectively. The results are analysed from an economical viewpoint and discuss

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00507.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.A 91‐day cage trial was conducted with juvenile seabass, Lates calcarifer (Bloch), and grouper, Epinephelus tauvina (Forskal), to ascertain the capacity of kerosene pressure lamps and fluorescent electric lamps as night‐lights above the cages to attract pelagic food organisms into the cage and consequently sustain the survival and growth of the cultured fish. The experiment was conducted using 1×1×1·5m floating cages with three different net mesh sizes (1, 13, and 19mm) and four fish stocking densities (seabass—10, 20,30 and 40/m3; grouper —10/m3). A positive growth response and survival was observed with seabass and to a lesser extent with grouper with increasing net mesh size and decreasing fish stocking density. At the lowest tested density of 10 fish/m3seabass survival increased from 5·0 to 95·0% and total cage fish biomass increased from −95·1% to +56·9% with an increase in net mesh size from 1 to 19mm over the 91‐day culture trial, respectively. The results are discussed in relation to the current commercial marine finfish cage farming practices emp

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00508.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.The determinants of shellfish aquaculture production in Atlantic Canada are investigated through the estimation of Cobb‐Douglas production functions, relating production output to several independent input variables. The statistical analysis is carried out for both mussel and oyster culture, based on data collected in a survey of aquaculturists. For both production processes, capital investment and labour usage have a significant effect on production output. In addition, the level of managerial experience (estimated by the number of years in operation) plays a significant role in determining oyster production levels. Increasing returns to scale seem to exist for oyster culture techniques, while mussel culture exhibits constant returns to scale. Furthermore, our preliminary analysis suggests that from a private operator's perspective, labour usage on the average mussel farm is roughly optimal, while for the average oyster farm, an increased use of labour could be profitable. In contrast, for both mussel and oyster culture processes, there appears to be no economic incentive for increased capital investmen

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00509.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Aspects of gametogenesis of the carpet‐shell clam,Ruditapes decussatus(L.), in two lagoons on the Atlantic coast of north Morocco were studied during December 1986 to February 1988. The clams sampled did not show any sign of hermaphroditism and the percentage of males was 42%. The gonads started developing in mid‐winter and were ripe in spring. Successive spawnings and reconstitution of gametes look place simultaneously starting from May up to the end of September. Two major spawning periods were noticed: a partial one in May‐June and a complete spawning in August‐September. From October to December the gonads were at resting stages. In coastal ecosystems where freshwater input is a very important factor, gametogenesis may be affected if clams are exposed to low salinities (less than 15%) for prolonged

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00510.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.In order to assess the attitudes of fish farmers towards data management, and discover the major sources of influence upon planning production, a postal survey among 293 salmon and trout farmers was conducted in the summer of 1987. The degree of microcomputer use and the uptake of automation were examined in this perspective.Salmon and trout fanners collected production records which, in most cases, were unsuitable for planning. Microcomputers were used mainly for accounting and word processing. Software was commonly purchased‘off‐the‐shelf’. Computerization when rejected was primarily on grounds of excessive costs and time requirements. Other automation comprised feeding systems and to a lesser extent water parameter monitoring. For decision making, directors and owners relied heavily on their site managers and foremen to provide feedback. When farms were members of marketing cooperatives or owned by larger firms the latter directed their production and outlets. Accountants were employed part‐time to draw the financial accounts, and the proportion of fish farms hiring experts and computer consultants was small. The findings showed that information technology is not a priority among fish farm

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00511.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY