摘要:

Abstract.We describe a rapid, non‐destructive method for determining lean body mass (LBM; i.e. total body mass — total lipid mass) and lipid content in live fish. This method provides non‐invasive determination of body composition by measuring the total body electrical conductivity (TOBEC) of an animal placed within a low‐frequency electromagnetic field. This principle is governed by the different electrical properties of body fat and fat‐free tissues. Relationships between TOBEC analysis and body composition were examined using juvenile sunshine bass (hybrid striped bass,Morone chrysops(Rafinesque) ♀×M. saxatilis(Walbaum) ♂) in a size range of 24–124g. Whole‐body conductivity was significantly correlated to LBM, lipid, protein, water, and ash content. Analyses of an independent group of fish indicated TOBEC to be a reliable indicator of body composition. This method should prove useful for deriving body composition data at various phases of an experiment or a life cycle, rather than a single point in time as with d

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00634.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.An investigation was undertaken to study the effect of 17α‐methyiteslosterone (17‐MT) on the sex reversal and growth of tilapia,Oreochromis spilurus(Günther), in brackish water (3–5 ppt) and sea water (40 ppt). Seven experiments were performed; four in brackish water and three in sea water. Yolk‐sac fry (1 or 3 day age) were immersed (7 or 24 h/day) in water containing hormone at a concentration of 0–10mg/l for 4–25 days. The swim‐up fry were subsequently fed either normal or hormone‐impregnated diets (30–70 mg/kg) for another 35 days starting from first feeding. The growth and SGR of fry were better in groups which received hormone both in water and food as compared with water or food alone. Immersion In 5–10 ppm (24 h/day) brackish water solution for 5 days did not bring any change in growth or sex ratio. However, immersion in sea water solution for 25 days (7 h/day) at a concentration of 1 ppm induced positive growth but no change in sex ratio. Higher doses either did not affect or reduced growth and SGR but induced higher percentages (77–83%) of males. Complete masculinization (100%) was observed only in brackish water when fish were immersed in 2·5 ppm solution for 4 days (24 h/day) and later fed 50 mg/kg in diets for 35 days. These results were further confirmed when the immersion schedule was modified to 10 days (7 h/day) and feeding 50–70 mg/kg hormone. It can be concluded from these studies that in brackish water complete masculinization ofO. spilurusis possible through immersion in 5·0 ppm for a minimum of 75 h followed by feeding with 50 mg/kg food for a minimum of 40 days

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00635.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.From February 1987 to September 1989, the monthly variations of eight indices of condition which are commonly used in bivalve aquaculture were determined forEgeria radiata(Lam. 1804) (Bivalvia: Tellinacea: Donacidae) from the Cross River, Nigeria. The indices were compared and their suitability for determining the spawning season ofEgeria radiatawas assessed. In general, a fall in condition index was observed during the rainy season (June‐October) and coincided exactly with minimum phytoplankton and pigment abundance. This decline in condition at the end of the wet season is as likely to be due to tissue depletion for maintenance under poor environmental condition as it is due to reproduction. The indices could be used as a quick and fast tool in assessing the spawning cycle of bivalves in the tropic

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00636.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.A study was conducted to obtain a measure of the potency of some potential and commercially used feeding attractants forPenaeus monodonFabricius. Behavioural trials monitoring the feeding response of the shrimp were used to gauge the attractant qualities of the substances. A growth trial recording the feed intake, feed assimilation, growth, food conversion and survival rates of the shrimp was used to assess further the feeding stimulant properties of the substances.Replicate groups of juvenile shrimp were fed semi‐purified diets containing 1·5% by weight of a range of potential feeding attractants.In the behavioural trial, diets containing taurine and a yeast extract were found to be significantly preferred to the control and all other diets. However, none of the substances appeared to act as potent feeding stimulants, producing statistically similar feed intake and assimilation rates to the control diet. However, taurine and an amino acid mixture designed to mimic a clam extract promoted the best performance of the attractants tested in terms of growth rate and feeding efficiency.Overall, the behavioural response of the shrimp to the feeding attractants was found to show similarities to the effects of attractant supplementation of feed on subsequent ongrowing performance, but not significantly

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00637.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.Oocyte maturation, ovulation and spawning were successfully achieved in the African catfish,Heterobranchus longifilisValenciennes, using frog pituitary extract. During artificial spawning, oocyte maturation and ovulation were induced at a dosage of 7mg per kg of individual fish weight. Latency period varied from 7 h at 29°C to 11 h at 25°C. Dead eggs became opaque between 8 and 10h after fertilization while embryogenesis was found to be temperature dependent. Mean hatching and larval deformity rates were 63·08%± 7·56 and 8·08%± 1·93 respectively. During induced natural spawning, the extract was applied at a dosage of 35 mg per kg of female fish weight. Spawning occurred between 10 and 11 h after hypophysation. Mean hatching and larval deformity rates were 41·38%± 8·48 and 10·00%± 2·00

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00638.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.Four cladoceran species of importance as fish food organisms, viz.Daphnia similes(Claus),Simocephalus vetulus(Schodler).Moina macrocopa(Straus) andCeriodaphnia cornuta(Sars), were raised in the laboratory on nutrient sources including manures, rice bran andChlorella.The organisms responded better with rice bran andChlorella.The productivity of culture organisms appeared to depend upon inoculum and residual densities, indicating a relationship between periodic harvesting and increased production. Associated study reveals the importance of space per individual in the success of laboratory cultures. The optimum space requirement of each species determined by the size of culture organism may vary from 4·5cm3per individual for small species likeCeriodaphniato 41·8cm3per individual for the larger species,Daphni

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00639.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.For initiating the development of tetraploid breeding lines in rainbow trout,Oncorhynchus mykiss(Walbaum), using different populations as a genetic basis, four populations out of a total of 11 were selected according to gene marker differences. Egg batches resulting from single‐pair and group matings and representing purebred and crossbred progenies of these populations were exposed to a late pressure shock for inhibition of first mitosis. In six out of 26 treated egg batches tetraploid embryos were identified by chromosome examinations. In the case of successful ploidization single‐pair matings yielded exclusively tetraploid embryos, while group matings contained some diploids. Successful tetraploidization was dominated by mating partners from one population. In total 413 putative tetraploid fry were available for further rearing. Besides diploids, triploids obtained by thermally induced retention of the second polar body were kept as controls mainly for methods to identify genome manipulated trout. Survival rates of tetraploids were low and loss frequencies did not stabilize till the age of 9 months. Thirty‐three tetraploid fish, individually checked by measurements of DNA content, nuclear cell size and number of nucleoli per cell, were found at the age of 17 months. Body weights of survivors were similar for tetraploids and diploids throughout the whole testing proc

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00640.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.In total, 10014 hatchery‐reared 1+ and 2+ rainbow trout,Oncorhynchus mykiss(Walbaum), were released near the mouth of the River Imsa, south‐western Norway, and in the Oslofjord, south‐eastern Norway. The reported recapture rate was significantly higher in the Oslofjord(15·4%) than at Ims(3·6%). Between 70 and 80% of the recaptures were made in the year of release. The fish were recaptured in rivers and the sea along the Norwegian coast, most of them near the release sites. In total, 60% were recaptured in salt water and 40% in fresh water. Fish released in the Oslofjord were largely captured with rod and line. Of those released at Ims most of the freshwater recaptures were made in a fish trap in the River Imsa. In salt water most fish were captured by nets. Specific growth rate varied inversely with body weight at release, decreased with time after release and decreased faster for fish released in the Oslofjord than at Ims. In general, the proportion of fish recaptured increased with mean fish weight at release. Recaptured biomass per 1000 fish released was higher when released in the Oslofjord (87·12kg) than at Ims (24·42kg). Stocking of rainbow trout in fjords is feasible and may contribute to local recreational fisheries. Yield was highest when relatively small (∼50g) fish were released. Economically, the best results may be obtained when the fish are released in nutrient

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00641.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.In 1991, the progeny of female Atlantic salmon,Salmo salarL., were sampled at emergence from sites in 16 rivers in western and northern Scotland. The progeny of farmed females that had escaped from sea‐cages were identified by detecting the presence of maternal canthaxanthin in the juveniles’ pigment load. Canthaxanthin was detected among fish sampled from 14 of the 16 rivers examined. Overall, 109 of the 2373 fry sampled carried canthaxanthin with an average frequency over all the rivers examined of 5·1%. This value will underestimate the real frequency of occurrence of the progeny of escaped farmed salmon: some escapees do not contain canthaxanthin and male fish do not contribute to the pigment load of their pro

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00642.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.Rod catches at four sites on the River Spey were analysed over the period 1970–1991. The year‐by‐year trends and seasonal patterns of rod catches varied according to site location. During the 1970s and 1980s the spring salmon catch from the Spey as a whole declined, mirroring a decline in catch at the lower sites in the river early in the year. Catches at the study sites did not always follow trends in the fishery as a whole, however, illustrating that the catch at any given site is not a simple function of the total number of available fish in the river. In the first 2 years of the 1990s the decline in early season catches continued, accompanied by a more general drop in catches throughout the angling season at three out of four

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00643.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY