摘要:

Two types of fat, represented by cod liver oil and lard, were added at various levels to the diet of rainbow trout. The food intake of the trout and their growth rate were measured. The results indicated that when cod liver oil was used as the fat supplement, the amount and the water temperature affected food intake and weight gain; fish fed on lard showed only a slight loss of appetite.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1975.tb04631.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

The age, growth, population densities and annual production of an isolated population of brown trout (Salmo truttaL.) and bullhead (Coitus gobioL.) were investigated over a 5 year period in Trout Beck in the northern Pennines. Additional data were obtained from two other sites; Great Dodgen Pot Sike and the River Tees.Trout growth rates were low, particularly in Dodgen Pot Sike, but ages up to VIII were recorded. Bullhead growth rates were similar to those in the Tees at Cow Green (Crispet al., 1974), though the Moor House bullheads had a higher survival rate. Population densities of trout ranged from 0.10–0.22/m2, with a fry contribution of 0.80%. The bullhead population in Trout Beck was sparse, generally 0.1/m2, though an 0 group value of 0.46/mawas estimated in 1967. At Tees Bridge values ranged from 2.5–7/8/m2. Most trout matured by age III, though in Great Dodgen Pot Sike only half of the females were mature at age IV.Annual production was estimated from Allen graphs. Trout production ranged from 1.02–3.50 g/m2/year, the fry contributing up to 51.5% of the total. A value of 0.48 g/m2/year was obtained for bullheads in the Trout Beck system in a year of good recruitment, whilst bullhead production at Tees Bridge was 7.43 g/m2/year, with fry and I group contributing 48.7 and 37.5% respectively. The high survival rate, irregular recruitment, and poor growth of these high altitude populations is discussed. Growth and reproductive peculiarities of the Great Dodgen Pot Sike trout are also disc

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1975.tb04632.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

Shad were sampled at four locations in the St John River area, New Brunswick; St John Harbour, Kennebecasis River, Washademoak Lake and Mactaquac Dam. The effect of the St John Harbour fishery on upstream spawning populations was minimal. Mactaquac Dam began operation in 1967 and since that time the populations of shad arriving at that facility have been in a state of flux. When shad populations from Kennebecasis River and Washademoak L. were compared, the Washademoak Lake population exhibited higher relative fecundity, lower mean age at maturity and possessed a lower proportion of repeat spawners. The combinations of reproductive characteristics occurring in the populations of the St John River were the same as those occurring over the Atlantic coast range of shad. The possible environmental factors influencing the variations in reproductive characteristics are discussed.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1975.tb04633.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

One tank of plaice in the W.F.A. Fish Cultivation Unit at Hunterston, known to habour an infection with the microsporidianGlugea stephani, was sampled over a 2 year period and showed a mean level of infection of 49.4 % with an apparent trend towards a decrease. Experimental oral transmission was achieved, without the use of intermediate or carrier hosts, and the dependence ofG. stephanion high temperatures was demonstrated. Most fish were able to tolerate the infection, but some mortalities in young fish were attributed to the parasite, particularly in the 2 months following the experimental infection. The parasite in the fish farm is believed to have been introduced with plaice stocks imported from more southern waters.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1975.tb04634.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

Salinity and oxygen tolerances of eggs and larvae of Hawaiian striped mullet (Mugil cephalusL.) were studied. Optimal salinities for eggs incubated at 19.5‐20.5°C were 30–32‰. Maximum larval survival occurred within the salinity range of 26–28‰. Significant decreases in egg survival occurred with eggs incubated in mean oxygen concentrations below 5.0 p.p.m. and for larvae held in mean oxygen concentrations below 5.4 p.p.m. The results are discussed in terms of spawning sites and the effects of oxygen saturation values on fish eggs

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1975.tb04635.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

The toxicity of zinc sulphate and cadmium sulphate to stone loachNoemacheilus barbatuluswas examined in an attempt to explain the distribution of the species in two polluted streams. Stone loach in hard water were more sensitive than rainbow trout to zinc, but much more resistant to cadmium. Their disappearance from the Willow Brook, Northants, in 1971–72 could be accounted for by zinc toxicity. A behavioural change, the loss of the instinct to hide during daylight, occurred in subsequently lethal concentrations of cadmium. The accumulation of cadmium in several tissues was also determine

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1975.tb04636.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

A northward extension of the range of the family Tripterygiidae is reported. Several specimens have been captured in the vicinity of Roscoff, North Finisterrc on the coast of Britanny, and presumed sight records from the English coast of the English Channel are reported. These specimens differ sufficiently from the four recognized European species to be regarded as taxonomically distinct. The nameTripterygion atlanticusis proposed for this species which is formally described.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1975.tb04637.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

Lake George, a shallow equatorial lake, supports aHaplochromisspecies‐flock of 17 species. Of the five species that dominate the species‐flock, two feed mainly on benthic and mid‐water dipteran larvae, one is a piscivore, one exploits microcrustacea and another the abundant blue‐green phytoplankton population. There is little stenophagy in this group. There is a seasonal variation in the total gill‐net catch of the three dominantHaplochromisof the sandy shoal habitat, with high catches in ths wet season and low catches in the dry. Similar fluctuations are known to occur in the commercial catches ofSarotherodon niloticus.No seasonal changes were observed in the proportions of the individual species making up this community and the individuals breed all the year round.A combination of ecologically unspeeialized species, resulting in an efficient exploitation and stability of the ecosystem may account for the observed high fish biomass and the high numbers of individuals. Taking into account the effect of the monotony of the environmental conditions, the physical continuty of the available habitat types and the relatively short time that the lake has been in existence, coupled with the apparent lack of rigid ecological requirements by the individual members of theHaplochromisgroup, it is suggested that this species‐flock may still be at an early stage in its evolutionary

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1975.tb04638.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

To monitor the perpetuation of triploid genomes in laboratory‐reared progeny of wild‐caught females ofPoecilia,amounts of DNA‐Feulgen staining in scale epithelial nuclei were determined for 58 different fish. Based on estimates of average DNA content, these specimens were readily separated into two groups: (a) diploids, with an average of 1–57 × 10−12g DNA per cell and (b) triploids, with an average of 2.38 × 10−12g DNA per cell. These values yield a ratio of 1: 1.5, as would be expected from the presence of an extra chromosome set in putative triploid females. Ploidy status of the latter, based on DNA cytophotometry, was independently confirmed for several specimens by direct cytological examination of chromosome number, by electrophoresis of plasma proteins and by morpho‐metric analysis. These findings unequivocally document one case involving the production of triploid offspring from a typical, diploidP. formosaand several instances in which broods of all‐female triploid offspring were derived in the laboratory from both wild‐caught and laboratory‐reared triploid mothers. The relationship and significance of these triploid forms to the breeding complexof P. formosaandP. mexicanain

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1975.tb04639.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

Vertebrae from 250Bagrus meridionalisfrom the southern end of Lake Malawi were used for age and growth determinations. There is a close correlation between ages determined from length frequency data and ages obtained by back‐calculation of the lengths when vertebral rings arc laid down. The rings are laid down annually, probably during the breeding season. Females grow slightly faster than males, the difference being in the order of 1–2 cm/year in the early stages. Recruitment to the trawl fishery takes place in the third year of life. Both sexes breed for the first time at the end of their fourth year. There is a much greater mortality in the male population after 40 cm in len

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1975.tb04640.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY