摘要:

Abstract.Since October 1986 living benthic molluscs from the eastern Weddell Sea, Antarctica (Fig. 1) have been kept alive in aquaria. Special equipment and methods have been used to reduce disturbance and laboratory effects during the long‐time rearing. Autecological investigations were carried out on behaviour, reproduction biology and growth of several polyplacophoran, gastropod and bivalve specie

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00590.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.Growth rates and fecundity ofBrachionus plicatilisfed baker's yeast, a diatom, and three different flagellates, were monitored during a 15‐day feeding trial. Identical growing conditions and equivalent food levels for the different diets were maintained during rotifer culture. The highest growth rate and mean fecundity were exhibited by rotifers fedChlorella saccharophila, followed in decreasing order by those fedIsochrysis galbana(T‐iso),Tetraselmis suecica, Saccharomyces cerevisiaeandThalassiosira pseudonana. Significant differences in contents of neutral lipids, polar lipids, sugars, glycogen, protein, ash and corresponding energy reserves in the resultant five groups of rotifers were diet dependent. Total available energy, about 15 kJ/g in rotifers fedS. cerevisiaeandI. galbana(T‐iso) was significantly different from the 14kJ/g in rotifers fedT. suecicaand C saccharophila, and in turn from the 13kJ/g in rotifers fedT. pseud

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00591.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.Simple body measurements were used to predict the fat content of Atlantic salmon parr. For three different sizes (wet weights 18–98g, 44–207g and 137‐151·8g) at two times of year (November/December and July) the percentage body fat (as measured by lipid extraction) could be predicted accurately using multiple regressions based on a combination of the following measurements: wet weight, fork length, opercular height, dorsal height, opercular width, dorsal width, anal width, adipose fin length and condition factor. In every case predictions based on multiple regression equations were more accurate than condition factor alone. This biometric method is easily employed and can potentially be used both in biological studies and on fish farms to assess body condition of individual fish. Since it is non‐destructive it has the additional advantage of allowing repeated monitoring of fat levels in the s

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00592.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.The eggs and yolk sac fry of the mouth brooding tilapia.Oreochromis mossambicus(Peters), were artificially reared in an experimental hatchery system at different temperatures. The hatchability, embryonic development of eggs and growth of yolk sac fry were studied under controlled conditions. It was shown that the upper lethal temperature forO. mossambicuseggs was above 40°C and the lower lethal temperature between 11°C and 17°C. For yolk sac fry these values lay between 34 and 40°C and 17 and 20°C respectively. Fry survival between 24·3 and 34·0°C was near to 100% while al 20°C it was less than 60%. The somatic growth rates of fry at temperature between 20 and 34·5°C up to 10 days post hatch are presented and were found to differ significantly. At 34·6°C a negative SGR was recorded during the period 6–9 days post hatching, but, during the first 6 days, the SGR at this temperature was more than four times higher than at 20°C. At the elevated temperatures, the utilization of yolk is faster and the loss of weight observed was due to starvation. This should be taken into account when incubating under artificial rearing condition so that initiation of exogenous feeding is timed mos

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00593.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.Arctic charr,Salvelinus alpinus(L.), from the same full‐sib family were reared under two different densities for 97days at 10°C. In one treatment density was adjusted every 2 weeks by means of a tank enclosure to a density of 50kg/m3. In the other treatment the density was allowed to increase as fish biomass increased to 50kg/m3. Density had no significant effect on the variation observed in individual fish weights over the course of the growth trial. Density had a significant effect on the relationship between fish weight and specific growth rate. The increasing density treatment had an overall higher mean specific growth rate of 0·1%/

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00594.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.Four feeding trials with Israeli carp, Cyprinus carpio L., were performed in cages or in ponds in order to investigate responses to lysine supplementation of low protein carp feeds under different practical conditions. In each of the trials one of the basic conditions was different: fish size—small (80–125g) or large (560g); temperature—22°C or 26°C; density—cages or ponds. In each trial 2–3 ration sizes × 2–3 lysine levels were tested. A basal diet of 25% protein and 1·35% lysine served for all the trials.At low feeding levels, no responses to lysine supplements were found either at 22 ± 2°C or at 26 ± 2°C (0600 h) for all fish sizes. At higher feeding levels, at both temperatures, 0·5% lysine‐HCl supplements to 1·7% total lysine yielded significant growth increases. Further supplements to 2·1% lysine (=8·4% of the protein) brought an additional response only from small fish of 90g in cages at the highest ration and temperature. In ponds at 26°C, the effects on small fish of 80g were smaller, probably due to available natural food. The reduction in lysine retention suggested that 1·7% lysine might have been adequate even at

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00595.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.The population density, growth and diets of eels,Anguilla anguillaL., from four sites on two rivers in eastern England were studied over 2 years. Eel population density varied greatly between sites and seasons, few eels being caught during the winter. Mean population densities ranged from 50 to 518 eels/ha and mean biomass from 35 to 210kg/ha. Older eels were more numerous at upstream sites. Growth rates in the two rivers were generally similar, but eels 9–13 years old at upstream sites were significantly larger in terms of length and weight than their downstream counterparts.Of 868 eels examined, only 425 stomachs contained food, the percentage of empty stomachs being negatively correlated with temperature.Asellus aquaticuswas the predominant food item at all sites in all seasons and in the three size classes of eels studied. Megaloptera and Trichoptera were also important. Fish, largely bottom‐dwelling species, were found mainly in the largest size‐class of eels and in the winter, when few large eels were feeding. Niche breadth expands with increasing size o

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00596.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.Pikeperch,Stizostedion luciopercaL., introduced into Lake Egirdir, in south‐western Turkey, in 1955 grew well and formed the basis of an export fishery. Recently their size has declined and there are now so few of filletable size that the fishery has reverted to supplying purely local needs. Only 2 of the original 11 fish species are still found in the lake and this study examined the possibility that the decline in size of the pikeperch might be related to diet. It was found that invertebrates remained the main food of pikeperch in this lake till they reached a much larger size than elsewhere and that cannibalism was much higher than had previously been reported. The indications were therefore that there was a lack of forage fis

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00597.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.This study was conducted to estimate spring hooking mortality of white crappie, Pomoxis annularis Rafinesque, in Buchanan Reservoir, Texas, USA and summer hooking mortality of spotted bass, Micropterus punctulatus (Rafinesque), in Eagle Mountain Reservoir, Texas, USA. Reservoir surface water temperatures averaged 19 and 31°C, during white crappie and spotted bass experiments, respectively. White crappie (mean total length (TL) 267mm, range TL 190–340mm, standard error (SE) TL 6mm) were caught with size 5 single hooks baited with golden shiner, Notemigonus crysoleucas (Mitchill), and spotted bass (mean TL 220mm, range TL 143–326mm, SE TL 7mm) were caught with artificial lures (spinners) fitted with size 4 or 5 treble hooks. Fish were held in cages for 72 h to observe delayed mortality. Four of 43 white crappie (9·3%, 95% one‐tail, upper confidence limit (UCL) = 13·7%) died and four of 47 spotted bass (8·5%, UCL = 15·2%) died. One of the white crappie that died was a sublegal‐length fish. The relevance of these findings to the management of white crappie and spotted bass sport fisheries is discussed. It is concluded that under any management strategy necessitating release of some portion of the catch of white crappie and spotted bass, high survival of that portion could

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00598.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.Nine samples of Atlantic salmon,Salmo salarL., from four different rivers in Asturias (northern Spain) and three different life stages (fry, parr, adult) were karyotyped. The distributions of 2n chromosome numbers in the samples were not statistically different, suggesting the AsturianSalmo salarpopulations have the same chromosomal polymorphism make‐up. They were, however, significantly different from populations in Scotland and Norway used to stock many Asturian river

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00599.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY