摘要:

Based on published data, we reviewed clinal variations in life‐history characteristics of anadromous brown troutSalmo truttafrom 102 European rivers at latitudes between 54 and 70° N. Growth rate in fresh water, mean smolt age, mean sea age at first sexual maturity, proportion of repeal spawners among adults, longevity, and length of adult life span exhibited latitudinal clines. Brown trout grew faster in fresh water, smolted and matured younger, lived fewer years but spawned more times in the south than in the north. The life‐history traits studied were often correlated. Longevity, smolt age and sea age at maturity were negatively and smolt length and proportion of repeat spawners among adults were positively correlated with growth rate in fresh water. Longevity was positively correlated with smolt age and sea age at maturity. The latter also increased with increasing smolt age. None of these significant correlations among life history variables, except for those between smolt age and parr growth and proportion of repeat spawners and parr growth, are latitudinal effects. We do not know to what extent the latitudinal variation in life–history traits reflects phenotypic plasticity and to what extent it is caused by inherited differences among popul

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb01175.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The possibility of deriving a prediction about the effect of seasonal variations in the duration of the planktonic larval phase on the dispersal of larval Dover sole was investigated. During six cruises, from February to May 1992, the distribution of sole larvae was studied along a 100‐km transect, from the offshore spawning grounds to the coastal nurseries of the Bay of Biscay (France). Samples (n= 189) were collected with a suprabenthic sampler, and vertical profiles of water temperature and salinity were recorded simultaneously. Counts of otolith increments of larval stage 4b (onset of metamorphosis) were used to estimate the duration of the planktonic life. Duration of the larval phase decreases by about 15 days (37%) with water temperature increase (between 8° in February and 11.2° C in May). Sole larvae occur from the coastal area to 100 km offshore. Within the same cruise, no difference in the duration of the planktonic life was observed between the larvae caught in the onshore and the offshore area. In spite of seasonal differences in abundance, the extent and the shape of the larval distributions during the period of study suggest that the seasonal variations in the duration of the planktonic life did not affect the larval distribut

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb01176.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The catches of a small artisanal fishery for flying fishes (Families Exocoetidae and Hemiramphidae) on the Danajon Bank in the Camotes Sea. Central Visayas, were recorded during a 14‐month period between 1987–1988. Catches were made using floating drive‐in‐nets deployed from small motorized canoes. Three species,Cheilopogon nigricans, Cypselurus opisthopusandOxyporhamphus convexus, formed about 90% of landings. Growth, mortality and related parameters for the three dominant species in the catch were estimated from length‐frequency data. Seasonal variations in catch rate and recruitment are described and thought to be linked to the two monsoon periods in the Philippines. Total mortality rates were very high and, while these may be the result of migratory movements rather than attrition, they are a cause for concern in such a highly selectiv

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00407.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The distribution of 0‐group flatfish was investigated in 1992 in the Dollard (Ems–Dollard estuary, Wadden Sea). 0‐Group plaice, flounder and sole were not evenly distributed over the sampled locations. The spatial distribution pattern of 0‐group flatfish in the Dollard changed during the investigation period. In the first week of sole presence, when the mean length of sole was 24–30 mm, salinity correlated significantly with sole density. The distribution of juvenile sole larger than 40 mm total length was affected by the elevation of the location: 0‐group sole was restricted to the sampled site with the lowest elevation. The distribution of 0‐group plaice was related to sediment: no juvenile plaice were caught at locations with more than 10% mud fraction in the sediment. The distribution of 0‐group flounder was also correlated with sediment. Later in the year, salinity correlated negatively with the distribution of 0‐group flounder. The influence of sediment composition is probably indirect and linked to the abundance of preferred food items, such asCorophium volutator. Abiotic conditions were suitable to 0‐group plaice

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb01177.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The feeding of bleak,Alburnus alburnus(L.), was studied in a natural eutrophic lake of northern Greece by an analysis of gut contents. Feeding was more intense during the first half of the day. Monthly analyses showed temperature‐dependent feeding intensities, which were high during summer and the beginning of autumn and showed a decline in winter. The low feeding intensity in April coincided with the maximal value of the GSI. Bleak is a zooplankton feeder mainly, consuming Copepoda andBosminaall the year round. During the hot period the diversity of its food increased. Other Cladocera, mainlyDiaphanosoma, but alsoMoina, Daphniaand other less abundant genera, were found also. Meanwhile, Hydracarina and insect nymphs were found frequently, but in very low quantities. The size of bleak did not play an important role in its food composition. The stenophagic nature of its feeding could be explained in terms of the abundance of zooplankton in the environment. The influence of feeding intensity on the condition factor of the species is discusse

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00408.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The River Usk catchment in South Wales supports mainly freshwater resident brown trout, with few anadromous fish. Electric fishing and netting revealed that age‐class distribution differed between main river and tributary habitats, the latter environment acting as a nursery area for young fish. Few fry were found at main river sites. Age‐class distribution also differed between tributary systems, and possible reasons are discussed. Trapping experiments indicated that trout move to main river habitat at 2+ yr. Lengths at age (back‐calculated from scale reading) were similar for main river and tributary resident fish at 1 and 2 year, but main river fish were larger at 3 and 4 yr. This habitat shift and size difference is discussed with reference to current angling regula

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb01178.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Many species of freshwater and anadromous fish are fragmented into local populations, some of which display adaptive traits that enhance survival and reproduction in particular environments. This paper focuses on the genetic component of response to heterogeneous environments, with emphasis on how the levels and distribution of genetic diversity may influence the distribution of conspecific populations. It addresses three aspects of genetic variability and adaptation: (1) the significance of genetic variability in relation to adaptation; (2) the adaptive significance of population differentiation; (3) the effects of stocking on local adaptation. In addition to considering local adaptation in salmonids, especially in relation to the genetic consequences of stocking, examples are chosen across fish taxa, with emphasis on recent studies in the guppy,Poecilia reticulata. The significance of within‐population genotypic variance in fitness traits, genetic load and outbreeding depression is discussed in relation to adaptation. Evidence for local adaptation is drawn from molecular investigations, genotypic selection experiments, and integrated breeding and field studies. The fragility and uniqueness of locally adapted gene pools is emphasized. Threats arise from direct interactions between native and introduced fish through stocking and escapees of cultured fish. Conservation of genetic resources must not only include practices that maximize levels of genetic diversity, but also measures to preserve the associated genotypic variance in ecologically‐significant traits. The integration of descriptive population genetic studies with empirical demonstrations of adaptive traits is encoura

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb01179.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Four sciaenid speciesJohnieops dussumieri, Kathala axillaris, Pennahia macropthalmusandOtolithes ruberwere analysed electrophoretically for genetic variation at 18 loci (16 inP. macropthalmusandO. ruber). Twelve loci were polymorphic inJ. dussumieri, 10 inK. axillaris, three inP. macropthalmusand 12 inO. ruber(P<0·99). Average heterozygosity ranged from 0·033 ± 0·100 to 0·070 ± 0·122. The allele frequencies of 14 loci were used to estimate Nei's genetic distance (D̄). The D̄ values ranged from 0·334 to 0·612. Three isozyme loci (LDH‐B*, MDH‐2*andG3PDH‐1*) were found to be the most reliable species

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00410.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

In white axial muscle of carp addition of new fibres to the muscle mass (hyperplasia) decreased with increasing length of the fish. This was deducted from the decrease in the amount of small fibres. In carp larger than about 40 cm standard length (s.l.) hyperplasia no longer occurred (small fibres were absent) and muscle growth only occurred by means of hypertrophy (growth of existing fibres). The stage of growth in which many new fibres were added showed a relatively fast increase in trunk weight, as calculated from growth curves. During the stage of fast growth with a high occurrence of hyperplasia, the DNA/protein ratio decreased. The high percentage of postmitotic myosatellite cells isolated from carp of 5 cm s.l. suggests that in hyperplasia a subpopulation of already differentiated myosatellite cells formed in an earlier stage of development is incorporated in new muscle fibres. The increase of the relative importance of hypertrophy appears to be correlated to an increase in the percentage of proliferating myosatellite cells 17 h after isolationin vitro. This suggests that in hyperplasia and in hypertrophy different subpopulations of myosatellite cells are involved.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00411.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Efficient foraging and a reduction in predation risk have been proposed as reasons for shoal formation. Some behaviours in cyprinid shoals are at first sight altruistic (e.g. predator inspection behaviour, reactions to alarm substance), such that kin selection may have been involved in their evolution. If shoaling behaviour does evolve through kin selection, then genetic differentiation is expected to be greater between shoals than within shoals. Such a hypothesis was tested here by examining shoal integrity and the relatedness of individuals within and between shoals in the European minnow,Phoxinus phoxinus, using nuclear and mitochondrial DNA markers. The breeding structure of 13 minnow shoals collected from Dorset and North Wales, U.K., was examined using allozymes. Genetic affinity within and between shoals was tested using mitochondrial DNA and multi‐locus DNA fingerprinting. Shoals consisted of a random assortment of allozyme genotypes, shoal members did not share the same maternal mtDNA lineages and DNA fingerprint profiles were as varied within shoals as between them. The data indicate that it is unlikely that kin selection occurs inP. phoxinusand there is no apparent relationship between shoaling behaviour and genotype distribution in this specie

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb01180.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY