摘要:

Hybrids between bream,Abramis brama, and roach,Rutilus rutilus, occur in the lower reaches of the River Exe and were positively identified by their meristic features and shape of the pharyngeal bone. The growth of bream and hybrids was determined by back‐calculation from scales. Annual checks were laid down in early June. The mean length for age of female bream was significantly larger than that of males for fish 6 years of age and older. This divergence in growth rate was associated with the sexual maturation of the fish. Data for the sexes were combined and compared with the growth rate of hybrids and roach from the same region. Hybrid growth was similar to that of bream for the first 6 years of life but was intermediate between that of the two parent species in the older age groups. Some hybrids with developing gonads were found. A change in the diet of bream from planktonic feeding to a benthophagic habit with age was noted. Detritus, substrate and chironomid larvae formed the bulk of the diet of hybrid

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb04223.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Seven juvenile whale sharks ranging from 550 to 930 mm in length are reported. Measurements of six are tabulated with remeasurements of the single known embryo. The mode of reproduction of this shark is again questioned, and the lack of records of sizes between 1 and almost 4 m is discussed.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb04224.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The purpose of this study was to investigate possible effects of organochlorine residues on cortisol balance in a freshwater fish. The combined stress of netting, handling and blood sampling inSarotherodon aureusnormally results in a twofold increase of circulating cortisol, within 30–60 min. Fish treated with o,p'DDD (50 mg kg−1) had higher resting level of cortisol than before treatment (155.8±12.7 v. 86.9± 11.2 ngmh−1; n=16). No further increase in cortisol level occurred in these fish after exposure to stress; this inability to respond was maintained for more than 120 days. A recovery of the response to ACTH by superfused interrenal tissue from the treated fish was observed 255 days after treatment. Successive blood sampling of o,p'DDD‐treated fish, injected intracardially with labelled cortisol, have shown that the half‐life of the steroid in the circulation is prolonged by 370% compared with controls. The hepatic metabolism of cortisol was studied by incubating liver slices with the labelled hormone. Hepatic tissue from o,p'DDD‐treated fish metabolized cortisol slower than livers from controls. The high resting level of cortisol in plasma of fish treated with o,p'DDD may be attributed to the retarded metabolism of the steroid by the liver. The lack of augmented cortisol levels in response to stress is attributed to the interference of the organochlorine with the response of the interrenal tissue to the stress‐induced surge of

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb04225.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

An intersex specimen of the banded killifish,Fundulus diaphanus, was encountered during the analysis of the annual gametogenic cycle of this species. The simultaneous presence of mature spermatozoa and ova suggests that the potential for self‐fertilization existed in this fish. The spontaneous occurrence of this intersex individual, although a rare event, indicates the potential for the development of the synchronous hermaphroditic condition under natural environmental conditions in this normally gonochoristic specie

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb04226.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

It has been proposed that population‐specific pheromones released by juvenile salmonids guide the adults on their homing migration (Nordeng, 1977). To evaluate this hypothesis, adult coho salmon,Oncorhynchus kisutch, were tested in a two‐choice apparatus with a variety of water sources. Coho salmon preferred home water without coho odours over an unfamiliar water source (city water). Adults preferred water conditioned by juveniles of their own population over plain city water, but did not prefer water conditioned by juveniles of their own population over that of anot

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb04227.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Grass carp,Ctenopharyngodon idella, and hybrid grass carp (grass carp ♀× bighead carp ♀Aristichthys nobilis), were fed duckweed (Lemnasp.), hydrilla (Hydrilla verticillata), chara (Charasp.), filamentous algae (Odogoniumsp.,Spirogyrasp.), and trout chow. Grass carp consumed all plants in greater amounts than hybrids. Grass carp grew best when fed hydrilla and trout chow and showed positive growth on all diets. Hybrids grew equal to grass carp when fed trout chow but did not grow on the vegetation diets. Low consumption rates of aquatic plants may indicate that hybrids are questionable as a plant biocontrol a

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb04228.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Growth of largemouth bass,Micropterus salmoides, in Lake Rebecca, Minnesota began in July and was associated with increased food consumption. Decreased maintenance levels and increased food consumption combined to produce maximum growth in September. Body growth andin vitro[14C]‐glycine uptake by scales varied similarly after the onset of growth; however, during the pre‐growth period, fluctuations in glycine uptake may have reflected physiological changes that were not detected by measurement of scale and body growth, but did relate to feeding activity. Patterns of glycine uptake and scope for growth were positively correlated (r= 0.74,P<0.05), which suggested that uptake may be related to general nutritional st

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb04229.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Arctic charr,Salvelinus alpinus, require diets with protein energy (PE): total energy (TE) ratios of at least 0.35 in order to maintain good rates of growth. The protein requirement is, therefore, similar to that of rainbow trout,Salmo gairdneri. Protein retention efficiency (PPV) declined as the protein content of the diet was increased, the relationship being described by the equation:It is suggested that charr will maintain good rates of growth if fed on diets used for commercial culture of rainbow trout and special formulations for charr should not be necessary.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb04230.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The theoretical limits of net reproduction rates for perch,Perca fluviatilisL. and pike,Esox luciusL, have been estimated from the upper and lower limits of fecundity, growth, mortality, age of maturity and biomass of parental stock, observed in Windermere over 40 years. Differences in egg numbers due to changes in fecundity were for perch × 1.5, for pike × 2. Assuming the same mortality, a fast growing cohort would produce more eggs during its lifespan than a slow growing, for perch × 2, for pike × 9. Changes in mortality from high to low resulted in more eggs, for perch × 7, and for pike (where high mortality includes natural and fishing mortality) × 10. Change in age at first maturity from 3 to 2 years was unimportant. Biomass of parental stock varied by × 6 for perch and × 3 for pike, and number of eggs laid varied by x2 for perch and × 5 for pike. The number of recruits at age 2 years varied by × 300 for perch and × 7 for pike. It was concluded that temperature in the first summer of life and predation were of major importance in regulating the number of recruits. Ricker recruitment curves and a simple model showed that perch, but not pike, could produce maximum recruitment from minimum parental stock. For perch, but not pike, compensatory density dependent mortality increased with increased parental stock. It was concluded that responses by the perch and pike populations to a changing environment can not be of sufficient magnitude to prevent wide fluctuations in r

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb04231.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Book reviewed in this articles:ANIMAL OSMOREGULATION, by J. Clifford Rankin and John A.MICROBIAL DISEASES OF FISH, edited by R. J. Roberts.RECENT ADVANCES IN AQUACULTURE, edited by J. F. Muir and R. J. Roberts.OCEANOGRAPHY AND MARINE BIOLOGY, an annual review, Volume 20. Edited by Harold Barnes (founder editor) and Margaret Barnes.PACIFIC PLATE BIOGEOGRAPHY (special reference to shore fishes) by Victor G. SpringerCOASTAL RESEARCH IN THE GULF OF BOTHNIA by K. Müller.THE PARASITIC COPEPODA AND BRANCHIURA OF BRITISH FRESHWATER FISHES (Handbook&Key) by Geoffrey Fryer. F.B.A.PHYSIOLOGICAL BASES OF PHYTOPLANKTON ECOLOGY by Trevor Platt.LAKE Mc l LWAINE (The Eutrophication and Recovery of a Tropical African Man‐Made Lake) by A. Thorn

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb04232.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY