摘要:

Total mercury concentrations were determined in the clupeid,Brevoortia tyrannus, from three estuaries of the Western Atlantic, and in the plankton on which they feed, as well as in the water sampled from the same localities. Although there was some indication that the food chain is a likely source of mercury contamination in these fish, as seen by the very much higher levels found in viscera compared with the rest of the fish, there was no evidence of strong food chain intensification. Fish mercury levels (0.3 to 0.5 part/106dry wt) were about twice that for plankton (0.1–0.2 part/106dry wt), with higher levels in phyto‐than in zooplank

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1973.tb04500.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

The grass carp has been introduced into many countries and yet self‐sustaining populations are known at four sites only outside its natural range. While the hydrological conditions apparently necessary for spawning are unlikely to occur in the U.K. the requirements of temperature and perhaps water speed occur locally in heated effluents from power stations. Since most heated effluents tend to layer on the water surface, grass carp eggs laid in effluents would quickly be exposed to falls in temperature of up to about 9°C. Experiments carried out in Austria with newly fertilized eggs show that incubation temperatures below 20°C result in large scale deaths, and deformities which lead to death, although 20 h old fry are not adversely affected. Because summer river temperatures seldom exceed 20°C it is concluded that if spawning did occur it would be unsuccessful at most power station sites. At sites where the power station uses a considerable proportion of the available river flow and where the effluent mixes completely downstream, eggs could possibly survive if temperature were the major criterion for successful develop

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1973.tb04501.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

Fish tagged as kelts at a number of Irish stations have been recaptured outside Irish waters along the coasts of Great Britain, Norway and West Greenland. Salmon tagged as smolts in three Irish rivers have been recaptured off the coast of West Greenland and one off the Faroes. Sixteen fish tagged as smolts in Denmark, Great Britain and Sweden were recaptured in Irish rivers or on the coastline of Ireland. Clean salmon tagged in the open sea have travelled to the coasts of Great Britain and a single fish travelled to southern Sweden. Feeding salmon tagged off West Greenland, in the Labrador sea and off the Faroes have been recaptured in Irish waters.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1973.tb04502.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

Estimates were made of the growth rates and proximate body composition of larval and metamorphosingP. marinus(L.) collected at various times of the year from Shelter Valley Creek, Lake Ontario. Analysis of length‐frequency data indicates that the average duration of larval life was 6 years, with metamorphosis occurring predominantly in the length range above 13 cm. Increases in length were almost entirely restricted to the warmest months and did not take place during the final year of larval life. Three categories were thus recognized for the proximate analysis: ammocoetes13 cm and metamorphosing individuals. In ammocoetes<13 cm, seasonal differences were observed in the regression coefficients in the logarithmic relationships between wet weight and length and between each of water, lipid and ash and the wet weight. No such difference was found for the regressions between protein and wet weight. For a fixed length (9 cm), the wet weight varied only slightly during the year, although a small peak was seen in May. When considered on the basis of fixed weight (1 g), the relative amount of lipid deposited was greatest in May/July, coincident with a high diatom density. The water content followed an inverse pattern to that of lipid, while the protein and ash contents showed little seasonal variation and exhibited values lower than those normally found in teleosts. Throughout the last year of larval life, the animal stored a greater proportion of lipid, presumably to facilitate the energy demands of metamorphosis during which this food store underwent a marked reductio

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1973.tb04503.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

The number of eggs spawned by female three‐spined sticklebacksGasterosteus aculeatus(L.) was highly correlated with the size of the fish expressed either as total length or as weight after spawning. There were no significant correlations between the size of the eggs measured either as wet weight per egg or as dry weight per egg, and the size of the fish. Nor were there significant correlations between the calorific value of the eggs and the length or weight of the fish. Regressions relating egg production to the length and the weight of the fish are given. These results and an analysis of previous studies on the fecundity of the stickleback suggest that variations in fecundity are primarily a reflection of variation in the size of the fish at maturity, and that this size is related to the race of the stickleback and to environmental conditions such as food supply which influence the growth of stickleback

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1973.tb04504.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

Aspects of the reproductive biology of the sprat in inshore waters of the west coast of Scotland were investigated from August 1970 to July 1972. Spawning in sprat lasts for a period of five to six months, starting in February‐March. Minimum size of maturity is 88–90 mm in both sexes but males tend to mature earlier in the season. Sprat shed their eggs in 7–10 batches. There is generally a higher proportion of females in the population. The fecundity ranges from 8700 to 46,600 in fish between 95 and 146 mm in length. It is significantly correlated to weight, length an

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1973.tb04505.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

Scales and opercular bones from 632 roach from the River Stour were used for age and back‐calculated growth determinations. The scales had clearer inner annuli but operculars clearer outer annuli in fish more than nine years old. The annuli were laid in late May or early June at the beginning of the growth period. Growth was minimal between November and April. Roach from both rivers grow faster than those in most other European waters. Female roach grow faster than males; River Frome roach faster than those from the Stour. Spawning occurred in May and elaboration of gonads between September and May. Immature roach have an annual cycle in condition with a maximum in June and a minimum in early Spring. The condition of mature females is affected by the gonad cycle. The fecundity of Stour roach is represented by the formula: log egg number=4.43 log length (mm)—1.69. Approximately half of the Stour males attained sexual maturity at age III and most of the rest by age IV. Half of the females were mature at age IV and the remainder by age V. Both brood success and growth rate varied from year to year but independently of one another. Most Stour roach ate aquatic insect larvae and molluscs but algae were more frequent in the diet of larger f

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1973.tb04506.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

An examination was made of some of the factors which influence the response to density in the guppy. Water from high density fish was given to fish populations kept at high and low densities. This induced high density behaviour in low density fish by increasing aggression and decreasing courtship. But giving ‘fresh’ water to high density fish failed to alleviate the response to density. ‘High density water’ slightly reduced the numbers of young found in low density groups. High density fish kept in the dark had more young than high density groups in the light; and the number of young found was decreased when ‘high density water’ was given to low density fish. The number of ovarian stages was decreased in the dark in high density and was not overridden by the type of water. Giving ‘high density water’ to low density fish decreased the number of oocytes stage III, but the interaction between water and ‘light’ was confounded by the total numbers of ovarian stages. Increasing the ‘visual space’ of high density fish with mirrors partially decreased aggression and increased courtship and number of young found; but had little affect upon the number of ovarian stages. Decreasing the number of physical contacts by keeping the fish chronically tranquillized reduced the activity of the fish. This reduced the aggression of the high density fish and also reduced the differences between the high and low density fish on the basis of their courtship scores, number of young found and number of stages in the ovary. Fish from differing population sizes were given a choice between varying fish densities. The fish from a ‘normal’ sized population and with an extended visual field, tended to make a choice conforming to the overall selections compared with fish from populations of extreme size and

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1973.tb04507.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

Guppy populations were established as one sex or mixed sex groupings, relative degrees of population density were obtained by manipulating the numbers of fish or the volume of the living compartments. Relatively high densities resulted in a reduction in the males courtship behaviour, affecting the number of dorsal fin erections, gonopodial swings, numbers of black spots, number of sigmoid reactions and courtship chases. These measures reached a peak at populations of 12–16 fish/1, falling off both below and above these densities. Associated with a rising fish density was an increase in agonistic behaviour. Activity was not affected by increasing density. Increasing fish density was associated with a drop in the numbers of young fish born and the number of stages occurring within the ovaries. These numbers were greatest at a lower fish density than the behavioural measure

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1973.tb04508.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

A rise in the haematocrit value of blood from rainbow troutSalmo gairdneri(Richardson) after collection into dipotassium ethylenediamine tetra‐acetate and storage is reported. Investigation using blood from brown troutSalmo trutta(L.) showed this effect can be due to a too low concentration of anticoagulant in the blood. The need for studying the effects of anticoagulants on the blood of other fish species is stresse

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1973.tb04509.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY