摘要:

The developmental stages of the gonads and the spawning season of the ocean whitefish,Caulolatilus princeps, were determined. Gonad maturation is annual, and the spawning season is prolonged, from late autumn to early spring. From November to March, around 80% of the females were in an advanced mode of gonadal development, and in April most gonads were spent. From May to October the gonads were at rest and preparing for the next spawning season.The gonadosomatic index describes the reproductive activity of the species adequately.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01233.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Nine polymorphic nuclear‐gene (allozyme) loci were surveyed among 491 red drum (Sciaenops ocellatus) sampled in 1988 and 1989 from nearshore localities in the northern Gulf of Mexico (Gulf) and the Atlantic coast of the southeastern United States (Atlantic). Data were combined with those from a previous study to generate a data set of 762 individuals representing 11 sample localities in theGulfand 175 individuals representing five sample localities in the Atlantic. The combined data set included individuals from the 1986 and 1987 year classes and permitted rigorous testing of both temporal and spatial genetic heterogeneity. Average heterozygosity‐per‐locus values (estimated using 33 assumed monomorphic loci) were 0·048 (Gulf red drum) and 0·046 (Atlantic red drum). Tests of heterogeneity in allele frequencies between year classes at individual localities and across regions (Gulf and Atlantic) were non‐significant. Tests of spatial (geographic) heterogeneity indicated that red drum are weakly subdivided: genetically‐differentiated subpopulations occur in the northern Gulf and along the south‐eastern Atlantic coast. Genetic data were consistent with the hypothesis that red drum within the Gulf and along the Atlantic coast comprise singie subpopulalions. Genetic differences between Gulf and Atlantic red drum seem likeiy to stem from historical or recent interactions between dispersal and impediments

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01234.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

The degradation of zooplankton eaten by vendace larvae was investigated by cutting their tubiform alimentary tract into four quarters and analysing the contents separately. Soft‐bodied rotifers were found to degrade and become indistinguishable in the anterior part of the alimentary tract, while cladocerans and copepods could still be identified in the posterior part. Assessing the diet of a larva on the basis of its whole alimentary tract contents was found to give biased results. More reliable estimates of the proportions of zooplankton taxa in the diet could be achieved from the first quarter of the alimentary trac

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01235.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Allometric growth of the stomach, intestine, and caeca was compared between two sympatric congeners, the copper rockfish (Sebastes caurinus) and the quillback rockfish (S. maliger), to examine the species‐specific differences in their gut tract in relation to their general feeding habits. The intestine of copper rockfish was shorter and its mass less than the intestine of quillback rockfish. Copper rockfish also had a greater stomach mass and, on average, a greater number of pyloric caeca than quillback rockfish. The differences in the gut allometry between the species were consistent with differences in their general food habits as copper rockfish consume proportionally more fish and larger crustaceans than quillback rockfis

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01236.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Lake Naivasha is a freshwater lake situated in the eastern rift valley of Kenya. Only five species of fish are present, all of which have been introduced. Of these,Oreochromis leucostictus, Tilapia zilliiandMicropterus salmoides(largemouth black bass) support an important gillnet fishery with bass also being taken for sport. Until bass reached 260 mm f.l. they depended upon invertebrate food organisms. Thereafter crayfish, fish and frogs became increasingly important the larger the size of the bass. The most important invertebrate prey species was the water boatman,Micronecta scutellaris, followed by chironomid and culicid pupae. Zooplank‐ton was consumed but only in large quantity by fish smaller than 80 mm. For bass over 260 mm the crayfish,Procambarus darkii, was the principal food. The largemouth bass in Lake Naivasha are generalized macro‐predators, feeding principally on free‐living animals of a kind most likely to be found in the littoral

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01237.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Silver carp and bighead carp exhibited size‐selection for food particles in aquarium experiments, but did not select their preferred species of plankton actively when they were distributed evenly in the water. They also possessed the capacity of selection for feeding area. The removal rates (% g−1fish weight) of silver carp for smaller plankton (phytoplankton) were higher than those of bighead carp. The removal rates by the latter for bigger plankton (zooplankton) were higher than those of silver carp, but for plankton about 70 μm dia. the rates by the two species were almost e

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01238.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Products of 24 presumptive enzyme loci were used to analyse the consequences on genetic structure and variation of theChondrostoma lusitanicumpopulation decline within the Tejo basin. This rare cyprinid is endemic to the Iberian Peninsula and has a very restricted distribution. Five samples from the Tejo catchment were compared with a sample from a small basin, the Samarra, that has not suffered obvious anthropogenic pressures and where the fish is still abundant. Heterozygosity and polymorphism were higher overall in the Samarra. Several lines of evidence indicate a high degree of population subdivision within the Tejo basin. In fact, about half of the total gene diversity detected in the Tejo population was due to differences among samples. This differentiation appeared to be caused by genetic drift and possibly differential local selection, coupled with reduced gene flow among localities. The accelerated process of habitat degradation occurring in the lowland streams of the Tejo basin will leadtothe inevitable reduction of intraspecies genetic diversity.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01239.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

The cytochromebgene is one of the protein‐coding genes of the mitochondrial genome that has gained importance because of the ease with which molecular techniques can be applied to the analysis of its structure. The nucleotide sequence of the largemouth bass (Microplerus salmoides) cytochromebgene was determined and the inferred amino acid structure is presented in the form of a structural model derived originally from rat cytochromeb. The inferred amino acid sequences from divergent animal species are aligned and compared in the context of this model. The data suggest that regions of the gene may be evolving at different rates due to different selection pressures associated with functional constraints. Conserved and variable regions of cytochromebhave been identified and can be targeted for species identification, the examination of intraspeciflc variation, and phylogenetic reconstructions in future researc

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01240.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

The main trophic interrelations were analysed in 12 species which represent 93% of the total catch from a beach seine fishery developed in Celestún, Yucatán. The diet was determined based on monthly samples over 4 yr. Five different trophic guilds were found on the basis of feeding preferences: microcrustacean and polychaete feeders, piscivores, omnivores and herbivores. For microcrustacean feedersOrthopristis chrysoptera, Eucinostomus gula, E. argenteusandOpisthonema oglinumthe diet is narrow with a large overlap between. For polychaete feeders,Arius felis, A. melanopusandHaemulon plumieridiet is broad with the higher overlap between the catfishes. Among piscivores,Bardiella chrysuraandHarengula jaguanahave a high overlap between them, but a lower one with other species from the community. Among omnivoresLagodon rhomboideshas the broadest diet and is considered to be a generalist whileAcanthostraceon quadricornisis a specialist having a very narrow diet and a lower value of overlap with the other species. Finally,Archosargus rhomboidalisis a herbivore with the narrowest niche breadth and lowest overlap. In addition to a description of diets and trophic inter‐relations, the results emphasize the importance to the beach seine fishery of the benthic food resour

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01241.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Calcium metabolism was studied in relation to ovarian functions and embryonic development during early and late pregnancy in the viviparous blennyZoarces viviparus. The level of total calcium in the maternal serum decreased during pregnancy from 21·7 (± 2·6) to 8·7 (± 1·1) mg 100 ml−1. Calcium in the ovarian fluid surrounding the embryos appeared at a level which was always lower than in the maternal blood. The calcium content of the embryos increased during their development in the ovarian cavity. During early pregnancy, oestradiol‐treatment increased the level of total calcium and alkkali‐labile protein P (vitellogenin) in serum of the maternal organism, but did not have any effect on the level of ultrafiltrable calcium. However, in the untreated females, the post‐ovulatory follicles, believed to act as calyces nutriciae in the pregnant ovary, were able to concentrate the ultrafiltrable calcium above the level in the serum. The activity of injected45Ca per unit plasma and follicular fluid volume was always higher in oestradiol‐pretreated fish when compared with controls over a time course range. Embryos from females, which were not treated with oestradiol, accumulated high levels of labelled calcium and the accumulation was time‐course dependent. Embryos from oestradiol‐treated females showed low levels of tracer accumulation at all samplings and their appearance indicated an overall negative effect of oestradiol. During late pregnancy, labelled calcium showed a rapid turnover within 24 h post‐injection in the maternal blood and ovarian fluid and a large accumulation in the embryos. Calcium influx in embryos, which were incubated with labelled calcium during 72 h inin vitrosystems was largest during the initial

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01242.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY