摘要:

Abstract.The fry of four species of planktivorous carp, silver carp,Hypophthalmichthys molitrix(Valenciennes), bighead carp,Aristichthys nobilis(Richardson), rohu,Labeo rohita(Hamilton), and catla,Catla catla(Hamilton), were grown in monoculture in ponds in Mymensingh, Bangladesh in order to determine electivity and the extent of dietary overlap. Other than an avoidance for Cyanobacteria, electivity was found to be low in most instances, although the low productivity of the ponds may have had some influence. Dietary overlap was greatest between catla and silver carp (0–52) and between catla and bighead carp (0–

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00518.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.One hundred and ninety‐eight fry of common carp,Cyprinus carpioL., were reared in outdoor tanks containing 9580 1 of water under five management schemes — separate live‐food system (LF), intermediate system (I), static manured system (M), manured system with water exchange (EM) and supplementary food system (SF) — in triplicate for a growing period of 90 days. Examination of frequency distribution of different weight groups of fishes at the time of harvest showed a maximum proportion of larger and smaller fishes in the live‐food and supplementary food system, respectively. Maximum growth and production of common carp in the LF treatment was the consequence of greater abundance of plankton food and improvement of water quality expressed in terms of higher values of pH and DO and lower values of CO

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00519.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.The aim of this investigation was to evaluate the phenotypic coefficient of regression of weight gain on initial weight as a correction factor in genetic testing programmes. A correction factor is required in order to remove the biasing effect of variation in initial weight among genetic groups tested, on their weight gain. In a genetic testing programme, involving common carp,Cyprinus carpioL., the environmentally generated coefficient of regression of weight gain on initial weight was used as a correction factor. It was estimated with the aid of the‘multiple nursing technique'. In other genetic testing programmes, not accompanied by multiple nursing, the phenotypic regression coefficient of weight gain on initial weight was used as a correction factor. These factors were compared by computing a series of each coefficientfrom a data set, consisting of the results of 10 yearly experiments and including 21 different experimental treatments. The results of this analysis showed that the phenotypic regression coefficient generated unreliable and often inflated estimates of the correction factor, relative to the estimate generated from multiple nursing, which we regard as reliable. Adequate genetic testing programmes therefore need to be accompanied by multiple nursing, unless test progenies are stocked at identical weight

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00520.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Hatching responses of the Japanese whiting, Sillago japonica Temminck et Schlegel, to a series of temperature changes were measured by exposing the fertilized eggs to eight constant incubation temperatures which ranged from 20·0 to 34·0°C. For a control, hatching temperature was kept the same as temperature of the ambient environment. Hatching responses were expressed as hatching percentages. Altogether 18 experimental trials were conducted during the natural spawning season of the species which extended over a period of 2 months from late July to mid‐September 1988, when seawater temperature varied between 24·0 and 30·0°C. Optimum and limiting temperatures were recorded and the data were optimally fit to the quadratic model. Results indicated that viable hatch occurred at almost all ranges of hatching temperature from 22·0 to 32·0°C. However, no hatching was recorded at either 20·0 or 32·0°C. The experiment showed that the optimum hatching temperature varied with the ambient temperature changes during the spawning season, indicating the latter to be a dependent factor for any hat

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00521.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.The effect of salinity on the survival and growth ofBatanga lebretonis(Steindachner) from the Lagos Lagoon, Nigeria was monitored in the laboratory for 24 weeks. Survival was excellent (90–100%) at all salinity levels tested except sea water. Growth rate differed significantly for the specimens held at 0·1, 5, 10, 15 and 20%o. The best growth in weight and food utilization was obtained at a salinity of

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00522.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Polychlorinated biphenyls (PCBs), chlorinated pesticides and mercury were analysed in cultivated eels,Anguilla anguillaL., and their food. In one experiment the eels were mainly fed with a low‐fat diet. In another experiment cultivated eels were fed a high‐fat diet. Both experiments showed that the major part of the organochlorine compounds and mercury present in the diet was retained by the eel. The retention of the organochlorine compounds and mercury was estimated at 50–70% after an exposure period of about 1 year.Although the mechanisms of accumulation of mercury and organochlorine compounds clearly differ, no differences in retention were found. The remaining mercury, PCBs and pesticides which were not retained possibly pass through the alimentary canal rather than being accumulated first and metabolized or excreted during the feeding period.Due to these high levels of accumulation monitoring levels of PCBs, chlorinated pesticides and mercury in the diet is essential for protection of the quality of cultivated

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00523.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.In temperate regions of North America, the culture of rainbow trout,Oncorhynchus mykiss(Walbaum), in ponds is constrained to the period mid‐November to early April by water temperature. Feeding practice may influence production time. The effects of three feeding practices on growth and body composition of rainbow trout raised in ponds during a 142‐day winter growth period were investigated. Feeding practices were (1) hand‐feeding to satiation, (2) feeding according to a fish size/water temperature chart, and (3) feeding by demand feeder.Fish fed to satiation consumed 66% more diet than fish fed according to a feeding chart and 163% more than fish fed by demand feeders. Fish fed to satiation had significantly higher (P0·05) between treatments. These data indicate that by using satiation feeding, marketable size rainbow trout can be produced in temperate region ponds without increases in percentage body fa

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00524.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Dorsal fin condition was evaluated in two groups of hatchery‐reared steelhead trout,Oncorhynchus mykiss(Walbaum), and compared to wild fish. Hatchery fish were reared either in nursery tanks with baffles or in isolation (1 fish/rearing space). Evaluations were conducted to determine differences in dorsal fin condition between these groups and to monitor the progression and severity of fin damage. Isolated hatchery and wild steelhead trout maintained perfect dorsal fins with characteristic white margins. Hatchery fish reared in nursery tanks with baffles experienced dorsal fin erosion that started when the fish were about 40mm total length (30 days after being on feed). This erosion continued until dorsal fin length averaged only 2·3 mm in fish 161–200 mm total length in contrast to an average dorsal fin length of 20·9mm in wild fish of the same

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00525.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Macrobrachium vollenhovenii(Herklots), the largest freshwater shrimp in West Africa, has been selected for culture in Nigeria. The oxygen uptake, metabolic rates and energy of inetabolism were investigated by known respiratory method in salinities of 0, 7, 15 and 20ppt. There were no significant differences in response to various salinities. This supposes similar physiological response to oxygen consumption with changes in salinity between 0 and 20ppt. These results are also discussed in relation to the culture conditions for the species.

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00526.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.This paper describes tests which were made to determine if smolt age at release influences the migratory pattern of three different stocks of salmon,Salmo salarL. The fish were hatchery‐reared and released in two different rivers, the River Imsa and the River Akerselv. Based on the tag returns we found that Baltic salmon from the River Neva, USSR differed in migratory pattern from two Norwegian stocks from the River Lone and the River Imsa. A large proportion of the 2+ River Neva smolts stayed in the fjord during the summer and autumn after release. On the other hand, 2+ smolts of the Norwegian stocks left the fjord and migrated to the feeding areas in the Norwegian Sea within a short time after release. The 1+ smolts of all stocks showed the same migratory pattern as the 2+ smolts of Norwegian origin. We propose that the observed differences in migratory pattern are influenced by the developmental rate of the smolts. The effect of developmental rate on the migration may differ among stocks. Our results show that it is possible to develop a fjord fishery by releases of 2+ smolts of Neva salmon. However, such releases must be carried out with the utmost caution, preferably in fjords with no salmon rivers, so that the possibility of gene flow between populations is minimize

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1991.tb00527.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY