摘要:

Reproductive mode of the two widespread speciesPolyprion americanus(Bloch and Schneider, 1801) andP. oxygeneios(Schneider in Bloch and Schneider, 1801) was investigated in specimens from New Zealand waters. Analysis of sex ratios, length frequencies and gonad morphology indicates that both species are primary gonochorists. Published suggestions thatPolyprionspecies are hermaphroditic and undergo sex change are rejected.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1989.tb02951.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The population of adult cisco in the Bothnian Bay consists of a number of spawning populations. Each one of these returns to the same inshore area for spawning every autumn. In the summer these populations are mixed and occur mainly offshore. These are the main conclusions of an experiment in which cisco were marked with Carlin‐type tags. The cisco were caught mainly in fyke nets both in the summer and in the autumn and released after tagging in the area where they had been caught. Fish tagged in the autumn and recaptured in the autumn one or more years later showed a strong affinity to the point of release, while fish from the same group recaptured in the summer had migrated far from the release site. The distribution of cisco that were tagged in the summer and caught in the autumn showed no correlation with the release sit

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1989.tb02952.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The effect of temperature and body size on oxygen uptake of European eels,Anguilla anguilla, was studied. The mass specific oxygen uptake of large eels was lower at all temperatures than that of small eels. The effect of temperature on metabolism was greater on small eels than on large eels. The relationship between oxygen consumption and body size is described by the equationM = a Wb, whereMis metabolism (O2h‐1), W is body weight (g),bis the slope of the function which describes the relationship between body weight change and metabolism, andais the temperature‐dependent constant of the equation. In this study it was found that increased temperature caused an increase inaand a decrease

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1989.tb02953.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The pH of sea water remains relatively constant at 7·8–8·3 but, in lower salinity environments, inshore and in estuaries, localized changes in pH can be caused by effluent discharge. Eggs and larvae of the Atlantic herring,Clupea harengusL., can be spawned and develop in these areas and thus may be exposed to acidic conditions. Larvae hatched from eggs exposed to sea water at pH 7·0 or 6·0 or 5·2, in comparison to controls, showed a significant reduction in the mean volume of muscle fibres and mitochondria, degeneration of mitochondrial cristae and swelling of the sarcoplasmic reticulum. These sublethal ultrastructural changes would cause reduced metabolic activity and loss of contractility leading to reduced swimming and equilibrium ability with consequent loss of via

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1989.tb02954.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Comparative scanning electron microscope studies have been performed on the skin of two oviparous and two viviparous freshwater fish embryos and larvae in order to investigate eventual morphological differences. In the early larval stages, temporary microvilli‐like structures (MVLS) were detected in oviparous fish larvae which were later replaced by raicroridge formations. In viviparous fish larvae, only‘fingerprint‐like’pattern microridge formations were observed. Light microscope slides showed that the disappearance of these MVLS were found to be chronologically related with the development of functional gill lamellae and yolk sac res

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1989.tb02955.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Hybrids between Atlantic salmon and brown trout were detected in two of four watersheds studied in northern Spain. The proportions of hybrids in samples of 'salmon’ranged from 0 to 7–7% but they were not significantly heterogeneous among locations, resulting in a mean hybridization rate of 2–3%. This is the highest rate of natural hybridization so far reported and is significantly greater than rates observed elsewhere in E

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1989.tb02956.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The development, verification and validation of a bioenergetics growth model for the European minnow,Phoxinus phoxinus, are described. Sensitivity analysis showed that the growth predicted by the model was sensitive to parameters used in the estimates of the energy and dry matter content of the fish and metabolic rate. The model gave good predictions of the form of the growth‐temperature relationship, but failed to predict the growth‐ration relationship well. Validation of the model against experimental data showed that the model underestimated growth at lower rations and overestimated growth at higher rations. Only at low ration levels did the model predict growth rates equivalent to those recorded for a natural population of minnows. Analyses of an empirical regression equation for growth rate, as well as the bioenergetics model, highlighted four areas for future research: (1) the energy content of fish in relation to environmental factors; (2) the feeding metabolism of fish in relation to environmental factors; (3) the regulatory mechanism of long‐term growth; (4) the effect of gonadal maturation on long‐term growth. The identification of these problems illustrates the advantage of a partially explanatory model, the bioenergetics model, over a descriptive empirica

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1989.tb02957.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The relation between number and size of spinal motoneurons and the dimension of myotomal muscle has been investigated in trout at different stages of embryonic, larval and postlarval development (body length 1–15 cm). Three spinal segments have been analysed (cervical, trunk and caudal) and the following parameters were determined by means of a Micromeasurements Image Analyzer: (a) mean cross‐sectional myotomal area; (b) mean soma size of principal (or dorsomedian, DM) and secondary (or ventrolateral, VL) motoneurons; (c) DM and VL motoneuron density per segment. Myotomal muscle and motor pool growth was evaluated by percent increments of a, b and c parameters at each stage. Their relationships were denned by equations of computed regression lines.The analysis provided evidence that: (1) a continuous exponential growth of mean myotomal area takes place in the three segments, with the same trend and with the lowest values in the caudal segment; (2) DM and VL motoneuron size and density per segment also increase during development, with the least value in the caudal segment, VL parameters being of lesser value than DM; (3) motoneuron pool and its target myotomal muscle parameters bear a linear relationship as defined by equations of computer regression lines; (4) motoneuron number percent increment at early eleutherembryonic stage precedes myotomal area increment which takes place during late eleutherembryonic stage.It is apparent that spinal motor pool and target myotomal muscle grow at the same rate in the trout during the considered stages. The discussion links this fact with the hypothesis of a neuronal influence on muscle fibre type differentiat

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1989.tb02958.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

A total of 668 specimens representing 18 species of meso‐ and bathypelagic fishes collected from the western North Atlantic were examined for parasites. Seventeen species and 39.1% of the specimens harboured at least one type of parasite. The highest number of parasite taxa recovered from a single fish species was seven. Host species had overall infection prevalences ranging from 10.0 to 88.9% of the specimens examined. Cestodes were most common (22.8% of all specimens examined), followed by fungi (6.6%), nematodes (6.1%) and digenetic trematodes (4.9%). Mesopelagic fishes showed a greater prevalence of infection (49.1%) than bathypelagic fishes (28.9%). Most parasites recovered were immature; however, based on the presence of adult and postlarval stage parasites, definitive and second intermediate host status is suggested for at least three fish species(Nemichthys scolopaceus, Nessorhamphus ingolfianusandEurypharynx pelecanoides). The presence of the cestodeNybeliniaandAnisakis‐lypenematodes among a number of host species may have been due to predation on the euphausiidNematoscelis, which was found in the stomachs of all host species infected by these two parasite taxa. Higher overall infection prevalences among host species were found than have been previously reported for mid‐water fishes and it is possible that this may be a function of near‐bottom presence of the fishes over the continental slope. It is suggested that the low prevalence of parasites within meso‐ and bathypelagic fishes when compared to benthic and shallow‐water species reflects the lower overall energy of, and reduced probability of host‐to‐host transfer in, the deep‐sea

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1989.tb02959.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The colonization by both resident and migrating spawner populations of brown trout and the characteristics of resident and migrating juveniles derived from the two populations have been studied in a brook and its tributary over 4 years. Resident trout spawns mainly in the upstream part of the brook and migrating trout in the downstream part. There are density and growth variations for the two age classes (0+ and 1 +) of juveniles in autumn according to the year and the environment. In the brook, the population of 0 + fish increases from downstream to upstream while the density of other age classes decreases. The migrating juvenile population of the brook changes annually and consists mainly of 1 s (one summer) individuals coming from the upper part. These individuals migrate generally in autumn and winter while young trout produced in the middle and downstream parts of the brook migrate mainly in the spring. The emigration process of the 0 + population decreases markedly from upstream to downstream and appears to be independent of the autumn length and sex ratio. In the tributary, most trout are 0+ years old, the population structure is different, and no migrating fish is observed. The results are discussed and a colonization strategy of the brown trout population in this brook is suggested.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1989.tb02960.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY