摘要:

Normal cod eggs respond to insemination by a rapid cortical reaction followed by an increase in total osmolarity and a small increase in egg diameter. The chorion becomes harder, but this is a slower process reaching its maximum strength afterc. 24 h. Bad eggs are characterized by a slower or incomplete cortical reaction, resulting in a slower rise in osmolarity and a softer chorion. Bad eggs rapidly lose their capacity for fertilization. In unfertilized eggs in sea water, no cortical reaction is observed. There is, however, a rise in total osmolarity and a hardening of the chorion.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb02877.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The skin mucus of rainbow trout, salmon, charr, cod, coalfish, plaice and redfish contain, besides lysozyme and haemagglutinins, protease activity. The mucus protease from rainbow trout has been purified, characterized and shown to be indistinguishable from the trypsin produced in pylorus caecae. This enzyme activity can escape detection in mucus since it is inhibited by serum components which may contaminate the skin mucus as a result of stress and handling of the fish prior to collecting the mucus.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb02878.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The reproductive biology of three introduced Poeciliidae,Gambusia affinis holbrookiBaird and Girard,Xiphophorus helleri(Günther) andX. maculatus(Heckel) was studied over a 14‐month period in Brisbane, Queensland. Photoperiod and water temperature determined the length of the breeding season inG. affinis, which produced up to nine broods between August and March, with the peak of reproductive activity in October. Fecundity was linearly related to body weight inG. affinis(mean fecundity = 22.78 ± 1.02, range = 3–108 offspring per brood).Xiphophorus helleribred from August to May, producing eight to nine broods, with peak reproductive activity from October to December. Fecundity was curvilinearly related to body weight (mean fecundity = 60.15 ± 3.8, range = 7–183 offspring per brood.Xiphophorus maculatusbred between September and March, producing five to six broods during the study period. Fecundity was linearly related to standard length (s.l.) (mean fecundity = 27.27 ± 2.4, range = 3–92 offspring per brood). Although the reproductive strategy of the three species differs, all have the capacity to build up large populations in south‐eastern Queensland. Their present distributions and relative abundance

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb02879.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Two hundred and seventy‐oneRaja clavatataken by otter trawl from the Solway Firth were examined for size, sex and state of maturity. Size relationships for both sexes were similar. Total length and disc width were linearly related as were disc width with wing width. Males and females appear to mature at 42 and 45 cm disc width respectively. The Solway population is heavily exploited by an unrestricted commercial fishery and a considerable proportion (48·6%) of the presently retained catch is immature. It is suggested that fishing pressure has brought about a reduction in the size at which female fish matu

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb02880.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The 10 species ofGalaxiasin Tasmania,G. olidusfrom mainland Australia and the four species ofParagalaxiaswere studied using principal co‐ordinates analysis (PCOA) and cluster analysis of a standardized Euclidean distance matrix based upon variate means, and by canonical variate analysis (CVA) conducted as a stepwise multiple discriminant analysis. Thirty‐five variables comprising 30 morphometric and five meristic characters were analysed. The meristic characters were not included in the CVA. Excellent separation of the two genera was achieved in all analyses. The multivariate analyses were repeated on each genus separately to see if relationships suggested by the overall analysis remain stable. When the resultant groupings of species are compared for the different analyses, no consistent, distinct groupings of species within each genus are apparent. Despite the absence of distinct groupings, some trends in the affinities of some species are evident. In particular, species affinities as indicated by the CVA are more consistent with established opinions of species relationships. From the results of the study it is suggested that caution be exercised in the application of multivariate statistical analyses of morphological data to ichthyological systematics and phylog

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb02881.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Critical swimming speeds (CSS) of sand smelt,Atherina presbyter, were measured in a laboratory flume. Individuals of all age classes (0+ to III +) found in the vicinity of Fawley power station, Hampshire, were tested at temperatures covering the seasonal range. The median CSS was 2.7 body lengths per second (bl s−1) at 5.8 °C, rising to 5.7 bl s−1at 18.5°C.A two‐variable (water temperature and body length) regression model was fitted to the data, and this was used to assess escape potential of fish coming into contact with the power station cooling water intake currents and the extent of possible bias in fish length data collected from this source. It is concluded that the sand smelt remains vulnerable to entrainment at the power station over its whole length range and over the full range of seasonal temperatures and that size‐dependent swimming performance will not lead to significant bias in sample length dist

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb02882.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

In the search for electrophoretically detectable protein loci in the Arctic charr,Salvelinus alpinus L., tissue samples of eye, liver, and muscle from a total of 934 specimens collected at 10 Swedish localities were analysed. General protein staining and specific staining for 33 enzymes revealed 52 detectable loci; 37 of which were considered usable in population surveys. Variability was observed at four loci coding for esterase (est‐2), the liver‐specific form of lactate dehydrogenase (ldh‐3), and the skeletal muscle form of malate dehydrogenase (mdh‐4, 5); genetic variation at loci coding forldh‐3andmdh‐4, 5has not previously been described in the Arctic charr. Relating our results to the multiple locus studies presented in the literature including Arctic charr from Ireland and North America reveals polymorphism at approximately one‐third of the loci studied in the Arctic charr, and the fraction of variable loci does not appear lower in this species than in other salmonids. There were highly significant allele frequency differences between samples. Nevertheless, there was a high degree of genetic similarity among all the populations sampled indicating that they were derived from a relatively recent common ancestor. The results are discussed in relation to the current controversy concerning the number of major evolutionary lines in Scandinavian

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb02883.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Excised liver sections of the milkfish,Chanos chanos, fry and fingerlings were studied by transmission electron microscopy. The hepatocytes underwent marked ultrastructural alterations in response to food deprivation of 10‐day starvation for fry and 2 months for the fingerlings. The prominent features characterizing the hepatocytes of starved fish were: a reduction of cell and nucleus size; apparent loss of nucleoli; condensation of chromatin material in fry; loss of stored glycogen; reduction of ER profiles; increase in the number of electron‐dense bodies containing large amounts of iron in fingerlings; and an increase in mitochondrial size. These changes were reversible following short periods of re‐feeding, i.e. 2 days for fry and 4 days for fingerlings, using natural food for the fry and formulated diet for the finger

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb02884.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The acute toxicity of nitrite (NO−2) to salmonids is strongly ameliorated by chloride (Cl−) ions rendering it almost harmless in most fresh waters apart from those with low Cl−content. In Cl−poor fresh water external NO−2is concentrated in the blood plasma until it is at approximately the same molar concentration as haemoglobin (about 8 mmol) and at this point most of the haemoglobin has been oxidized to methaemoglobin this being a contributory cause of death.Two theories are advanced to account for NO−2concentration in the blood. The first supposes that gills are impermeable to NO−2but allow its conjugate acid nitrous acid (HNO2) to diffuse into the blood where it dissociates according to the blood pH value. Thus NO−2will accumulate in the blood plasma if it has a higher pH value than the water. The second supposes that the Cl−uptake mechanism in the freshwater gill has an affinity for NO−2and accounts for the fact that NO−2entry to the blood is suppressed when external Cl−is present in significant amounts.The results also suggest that NO−2and Cl−behave similarly as diffusing ions. Thus NO−2diffusion into the blood of seawater fish and from the blood of NO−2loaded freshwater fish occurs at approximately the same rate as the corresponding Cl−fluxes. Nitrite loss from seawater fish is thought to be mainly by diffusion although there is some evidence for the active Cl−extrusion mechanism

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb02885.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Relative growth intensity of various longitudinally measured body segments in larvae of several species of fishes was distributed across the body in a continuous, U‐shaped gradient. Juveniles lacked a simple pattern of growth but appeared to grow nearly isometrically. Body depth exhibited a shallow, U‐shaped gradient while body width lacked a discernible pattern. Most intense growth, in three orthogonal planes, occurred posteriorly, probably promoting effective swimming early in l

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1983.tb02886.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY