摘要:

Groups ofPuntius gonionotuswere brought into breeding condition by treatment with extracts of homoplastic pituitary material. Spawning inP. gonionotusincludes a number of distinctive features which appear to be adaptations to reproduction in a riverine habitat. These features include the absence of a specific substrate requirement, the production of non‐adhesive, buoyant eggs, an elaborate circling display by the male, and a long spawning run during which gametes are dispersed across the current.Spawning activity began 3–4 h after treatment with pituitary material. The relatively sudden increase in female responsiveness and attractiveness to males appears to coincide with the occurrence of ovulation. It is hypothesized that at this time the female releases a chemical signal which attracts and excites the male. Females participate in a number of spawning runs over a period of 30 min, thereafter female activity decreases rapidly.Injections of a prostaglandin (PGF2a) were effective in inducing spawning activity in non‐gravid females. This finding provides support for the hypothesis, based on work with goldfish,Carassius auratus, that prostaglandin provides a link between periovulatory events in the ovary and the brain mechanism governing spawning act

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04289.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Food composition and feeding habits of 102 specimens ofAstatotilapia (Haplochromis) flaviijosephi(Lortet, 1883), collected in Lake Kinneret during 1973–1975 and 1981–1982, was studied.A. flaviijosephiis relatively abundant in the littoral zone of the lake. Females feed mostly on chironomid larvae, oligochaetes and amphipods whilst males consume mostly gastropods. Small fry are rarely preyed upon or collected by both sexes. The adaptive relation between the teeth and the type of food and the ecological statusof A. flaviijosephi inthe Kinneret ecosystem is discus

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04290.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The genetics of disease resistance in fish is examined. Major genes may cause skeletal or other phenotypic deformities and have also been implicated in the development of neoplasia. Others may affect viability through pleiotropic effects, or induce stress and therefore predispose to invasion by pathogens. Resistance usually appears, however, to be of a multifactorial nature. Variations in resistance between related species and between populations of the same species are described. In order to obtain an idea of the within‐population variation, heritability estimates have been obtained in some instances. Generally they are low, but may still indicate a sufficient level to be of use in a selection programme. The results of a limited number of selection programmes are describe

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04291.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

This paper describes the age determination of European yellow eels from a brackish water area in south‐east Norway. Two different methods were used; clearing in 96% ethanol or burning and cracking. When reading the otoliths twice using the same method, the same age was found in 40% of the readings, a discrepancy of 1 year was found in another 40% of the readings (both methods). Burning and cracking yielded age estimates which were on average 1.25 years higher than those obtained by clearin

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04292.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The general composition and diversity of the diets of the 43 most commonly caught pelagic and demersal fish of the Rockall Trough, north‐eastern Atlantic Ocean, are assessed. The fish are divided into three Groups. The 8 species in Group I consist of both pelagic and demersal species feeding on relatively few prey‐classes and having a diet of low diversity and few items per meal. Group II contains 22 pelagic and demersal species with more diverse diets, less restricted dietary composition, but still consuming relatively few items per meal. Group III is the 12 demersal macrourid species with the most diverse diets, a variable dietary composition and the greatest mean number of items per meal. One species,Maurolicus muelleri, had too many unidentified components in its diet to allow classification in terms of Groups I, II or III. All diets contained dominant items, the diversity within diets offish in Groups II and III arising from the inclusion of subdominants and rare items. The diets of species in Groups I and II can be defined in terms of ecological constitution, trophic diversity and prey‐species composition. Those of the Group III macrourids differ in that their definition is liable to be a compromise between the situation where ecological constitution and trophic diversity are adequately defined but not species compos

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04293.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Otoliths of eels recaptured up to 5 years after tagging were used for comparative work on the determination of annual ring patterns. It was possible to locate false annuli caused by the tagging procedure and subsequently to define annual rings in otoliths within the known period between first tagging and final catch. This determination gave an estimate of the size of the annual zones. Growth depression caused by tagging could be shown in cross sections of otoliths. Well defined annulus patterns in micrographs of otoliths from tagged eels were compared with otoliths from untagged eels. This comparison allowed a dimensional calibration of the ageing method and the recognition of misleading additional rings. Mean annual length increments of 47.88 mm and Lx, of 123.3 mm were determined.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04294.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

X‐ray studies of gastric emptying ofPleuronectes platessaforce‐fed a moist, artificial diet give the relationship:where GET is gastric emptying time (h),Sis meal size (g),Wis body weight (g) andTis temperature (°C).The corresponding gastric emptying curve is predicted to be:where stomach contents (g net weight) areS0at start andStat time th. Direct observations of residual stomach contents using serial slaughter are in close agreement with the predicted curve, save for small plaice (below 50 g body weight) which empty at only 50–60% of the rate found in larger fish.The small effects of body weight on gastric emptying rate may reflect the relatively small role of the stomach [Volume (ml) = 0.024 body weight (g)] in digestion when compared with other flatfish.The emptying curve established here can be used in field studies to estimate feeding rate on natural food items, provided fish greater than 50 g body weight are used and the energy density of the food is greater than 0.5 kcal/g wet weight. Smaller fish will have emptying rates which are only 30–60% of those found in larger fish; the change appears to be abrupt and corresponds to the size at which young plaice move offshore from their nursery

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04295.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

A total of 1145 stomachs from Atlantic salmon caught over the shelf off Helgeland/Trøndelag, and in the oceanic waters off Andenes, northern Norway during late winter–spring, 1969–1972 were examined. Food was found in 52.9% of the stomachs examined. The most important food items found in fish caught in the Helgeland/Trøndelag area were euphausids and hyperid amphipods while the myctophidBenthosema glaciale, the squidGonatus fabriciland euphausids were found most frequently in the salmon caught off Andenes. Most salmon had preyed upon only one species, and few stomachs contained three or more prey species. The type of food did not appear to be related to the length of the fish. It is suggested that some mesopelagic feeding occ

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04296.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Intensive culture of grass carp and hybrid grass carp(Ctenopharyngodon idellaxAristichthys nobilis) larvae was conducted under Florida (U.S.A.) conditions. The influence of different rearing facilities (indoor tanks, outdoor tanks and cages) and different methods of fish feeding using live zooplankton and artificial food was tested. High survival (86–100%) and satisfactory grass carp growth (47–56 mg) were obtained in the outdoor tanks and cages during the 10–day experiment. It is believed, that the technique described can be used after some improvements for commercial–scale grass carp larvae rearing. Low survival (1–3%) was obtained in the hybrid culture experiment even though satisfactory growth rates (84–212 mg) were obtained after 13 days. High mortality was attributed to genetic abnormalities caused by hybridization. The hybrid does not appear to be a promising fish

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04297.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

A modification of a previously described method of fish blood lymphocyte culture is described and discussed with the results of various chromosome banding protocols as applied to fish chromosomes.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04298.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY