摘要:

The temporal pattern of breeding by chambo,Oreochromisspp., and the vertical and horizontal distribution of territorial males at the Golden Sands‐Chembe beach were examined in the Cape Maclear region of Lake Malawi National Park. The breeding season began in September and ended in April, and the number of breeding males between 3 and 15 m was approximately 25 ha. Along the beach studied, the highest concentrations of nests were found at the ends of the beach near rocks, and the lowest number of breeding males occurred in front of Chembe villageResults from experimental gill netting demonstrated that the catches of chambo within the 100‐m Lake Malawi National Park ‘no fishing zone’ were identical to those outside the 100‐m zone, suggesting that fishermen would suffer little or no loss in catch by being encouraged to fish more than 100 m from the shore. Such a reduction in fishing and disturbance of the shallow water breeding grounds would probably enhance the chambo fishery. Preliminary data are provided on the chambo nest forms found in the Cape Maclear region, and further research is suggested to resolve the question of how many species comprise the genusOreochromisin La

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05529.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Stickleback males were implanted with Silastic capsules filled with 11‐ketoandrostenedione or androstenedione at the end of the breeding season. 11‐Ketoandrostenedione prevented the natural decline in secondary sexual characters and testes weight. It also completely inhibited the commencement of spermatogenesis, which normally takes place in late summer after having been quiescent during the breeding season. Androstenedione also exerted these effects, but to a lesser deg

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05530.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The development of the alimentary tract in larvaeof Coregonus ferafed withAnemianauplii has been examined histologically from the 4th to the 24th day after hatching.Buccal cavity and oesophagus are nearly completely developed before the start of feeding. The stomach exists only as an ‘anlage’, but starts to store food during the study period. The intestinal absorptive cells are stuffed with fat vacuoles between the 7th and 13th day after the start of feeding. During this time the rectal absorptive cells contain one large supranuclear body consisting of protein. The occurrence of large vacuoles in the intestinal and rectal absorptive cells may be caused by a partial non‐functioning of the larval digestion; after two weeks of feeding this restriction seems to be ove

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05531.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Growth of white axial muscle fibres of ten species of freshwater teleosts from five families (Cyprinidae, Centrarchidae, Percidae, Salmonidae, Esocidae) possessing widely different growth rates and ultimate sizes have been studied. The dynamics of muscle increase (i.e. increase in fibre numbers and/or diameter) appears to determine the ability for rapid somatic growth and large ultimate size in teleosts. Thus, the largest and fastest growing species (smallmouth bass, lake whitefish, rainbow trout, muskellunge) show evidence of sustained recruitment of muscle fibres to a large size, in contrast to the smaller and slower growing species (bluntnose minnow, longnose dace). Pumpkinseed, bluegill and yellow perch are all intermediate in fibre growth dynamics, growth and ultimate size between the smaller and larger species. Moreover, the ability of teleosts to grow rapidly and attain a large ultimate size is dependent on the body length at which recruitment of new muscle fibres into the growing axial muscle ceases. The regression equation,y=– 0.29 + 2.26 (x), showing the relationship (r = 0.95) between ultimate body length,x, and fork length at cessation of recruitment,y, indicated that for these teleosts, recruitment tends to cease when the fork length reaches about 44% of the ultimate body length. Possible mechanisms to account for this relationship are proposed, and the role of the ultimate fibre diameter in posing limits to the ultimate size of the species is discusse

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05532.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Rainbow trout were sprint‐trained (30 s duration) once or twice on alternate days for a period of 6 weeks. Swim speed for the first 10 s of a training bout averaged 11.4 bls for group 2 (trained once) and 10.2 bl s−1for group 3 (trained twice). Food consumption, growth rate and conversion efficiency were measured over 2‐week periods. Food consumption was 31‐38% less for the trained groups than for the control group (group 1). The growth rates of control and trained fish increased gradually over the training period. The growth rate of trained fish was always significantly less (48‐81%) than that of control fish. Although conversion efficiency was significantly less for group 3 at the beginning of training, no other significant differences in conversion efficiency were recorded. Maintenance rations were high in the initial period for all groups, but were lower than the initial values in the second and third periods. While condition factor was significantly lower for the trained groups, there were no differences in percent tissue protein, lipid, or

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05533.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Annual changes in the spermatogenetic activity of the testis were studied histologically in the river sculpin.Coitus hangiongensis, sampled monthly from a river in southern Hokkaido, Japan. A pair of sperm reservoirs, consisting of many anastomosing lacunae, was present along the dorsomedian edge of the paired testes, and functioned also as a sperm‐transporting system instead of the typical sperm duct. Spermatogenesis occurred actively in August, yielding an increasing number of mature spermatozoa in October. This process advanced, but slowly during the succeeding winter months, until March. The testis became functionally mature during the spawning period in April and May. In July, small numbers of spermatocytes were found to have appeared already, which indicated a relatively short period of post‐spawning testicular regression. In November, germinal cysts containing aberrant binuclear spermatids began to appear within the seminal lobules. The paired nuclei of aberrant spermatids gradually enlarged, and the cells were released into the lumina of the seminal lobules simultaneously with the release of mature spermatozoa from the germinal cysts. During the functional maturity stage, lumina of seminal lobules which had expelled mature spermatozoa to sperm reservoirs became filled with these abnormal bodies. Discussion includes the occurrence of aberrant spermatids which resulted in the formation of ‘spermatid masses’ as has been described in other

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05534.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

A mobile system incorporating a novel transmitter for tracking the position of freshwater fish is described. The transmitter emits both acoustic and radio pulses simultaneously to allow a range estimate from the delay between signals arriving at a receiver station. Results of field trials are presented and the usefulness of the system is discussed in relation to other tracking methods.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05535.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Two cohorts of Atlantic salmon parr and one of brown trout were studied in periods with and without the presence of mink,Mustela vison. In all localities a marked increase in mortality rate was observed during periods when mink were present. Mink were observed catching salmon parr, and approximately 10% of the parr had bite marks, especially on the tail fins. In the smallest stream with brown trout, the mortality rate was 0.80 during a few days with mink present; remnants of trout were found along the stream. The present study suggests that mink predation may be a major cause of mortality of salmonids in small streams. The results indicate that predation efficiency may vary with characteristics of the habitat, especially stream width and discharge, and fish density.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05536.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The external morphology of diploid and triploid grass carp was studied to determine whether the two types could be separated by differences in external characteristics. In a comparison of 27 measurements, six scale counts and five fin formulae from two stocks of diploid and triploid fish obtained from commercial producers, analysis of covariance and discriminant analysis indicated a classification accuracy of only 65–85%. Clearly, triploid grass carp differentiated by external morphology alone should not be stocked into waters where diploid fish are illegal or would cause management problem

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05537.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Otoliths of Atlantic salmon,Salmo salarL., are more slender than the otoliths of brown trout,Salmo truttaL. Discriminant analysis on otolith measurements of juvenile Atlantic salmon and brown trout from four river systems revealed a discriminant function which distinguished more than 94% of the cases. This function was tested by using data from a fifth river with cohabiting Atlantic salmon and brown trout: all Atlantic salmon and 91 % of the brown trout were correctly classified.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1988.tb05538.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY