摘要:

Abstract.In southern Africa rainbow trout,Oncorhynchus my kiss(Walbaum), are generally cultured at temperatures between 18 and 22°C, which is higher than the optimal thermal range for maximum growth in this species. Experiments were undertaken on two size classes of fish (25g) to determine the gross changes in protein and lipid requirements at these temperatures. The optimal protein and lipid requirements of the smaller fish were found to be 40% and 20–30% of the diet respectively. These levels are significantly different to those under optimal thermal conditions. The protein requirements of the larger fish remained at the ‘threshold level’ of 35% of the diet, although lipid requirements rose lo between 20 and 23% of the diet. The results are discussed in terms of the animal's scope for

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00604.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.Triploidy was induced in three full‐sib families of sea bream,Pagrus major(Temminck&Schlegel), by subjecting the fertilized eggs to cold‐shock treatment at 0°C for a 12 min duration, starting 3 min after insemination. Results showed that this treatment gave 100% triploid fish with reasonable survival rates of more than 61% up to first feeding, Triploidy induction was proved by the use of allozyme markers at three (ADH*,EST* and6PGD*) loci and red blood cell size analysis.At 2 months of age, the survival of the triploid group was lower than that of the diploids but it was comparable at 10 months. No differences in growth rate between diploid and triploid full‐sibs were observed up to the age of 10 months. However, differences in body weight between families were noticed both in diploid and triploid groups when cultured in the same net cage. This possibly suggests a high heritability for the trait examined in the broodstock. The gonads of the triploid fish were significantly smaller than those of the diploids, Histological analysis of the gonads revealed sterility in triploi

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00605.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.This study concerns the effect of feeding artificial diets containing varying levels of dietary protein (13%—49%) on the growth of fingerling pearl gourami,Trichogaster leerii(Bleeker, 1852). The growth rate increased significantly with increasing dietary protein content, but it was observed that the increase in growth rate was faster within the 13–32% range than in the 32–49% range. Feed utilization efficiency increased, and protein efficiency decreased, with increasing dietary protein. On the basis of this study, the optimum dietary protein level forT. leeriiis between 26 an

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00606.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.Dry and freshAzolla pinnatawere evaluated as feed ingredients for fingerling and adult Nile tilapia,Oreochromis niloticus(L.). DryAzollawas incorporated into practical diets containing approximately 30% crude protein and 360–400kcal/lOOg of GE lo replace 25,50,75 and 100% of the fish meal (FM) protein in the control diet. FreshAzollawas also tested as a total diet for these fish. Formulated diets were fed to duplicate groups of fingerling (2–54g ± 0093) and adult (4033g ± 103) fish at a daily rate of 5% and 3% of their body weight respectively for 10 weeks. Growth and feed utilization efficiency of fish fed the control diet were significantly higher than of those fed Azolla‐supplemented diets. Fish performance continued to deteriorate with increasing dietaryAzollalevel in the diets. This reduction was extremely sharp when dry and freshAzollawere used as total diets. Furthermore, adult tilapia fed freshAzollastarted losing weight from the 7th week. Fish fed freshAzollahad significantly higher moisture content than those fed formulated diets. Body protein and lipid contents were negatively correlated withAzollalevels in the diets, while body ash content showed a positive correlation. Results of this study indicate that young Nile tilapia utilizesAzollamore efficiently than the

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00607.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.Clarias isheriensisSydenham fingerlings (60·42 ± 1·13g) were fed for 180 days with pelleted diets in which maize was progressively replaced with graded levels (0, 15,30,45%) of cocoa‐pod husk meal (CPHM). There was a decline in growth rate with increase in dietary CPHM level, though this was not significantly different (P0·05). Fish mortality was low (0·05) differences among the feeding regimes tested, with regards to growth, feed conversion and fish yield. This suggests that the growth ofC. isheriensisfrom fingerling to adult size (≥ 200g) can be satisfied in one single feeding equivalent to 3% body

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00608.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.The sperm of tench,Tinca tincaL., is characterized by a milky colour and consistency, and is of very low density. After collecting the sperm, motion of spermatozoa was recorded even without water activation. A better motility value (value 4·36 on average) was observed in spermatozoa collected in immobilizing solution (collecting medium) and stored for 3h, when compared with spermatozoa without collecting medium. Average total and relative numbers of spermatozoa were 12·16 × 109per male and 18·50 × 109per kg of body weight, respectively. When testing the effect of activating solution in artificial propagation of tench, the highest fertilization rates (81·3 and 85% in two cases) were found for NaCl solution with an osmotic concentration of 34 or 69 mOsmol and for fresh water, respectively. The fertility rate was reduced significantly (P<0·01) by any increase above 105 mOsmol in NaCl concentration in the activating solution. In the tests of optimal method of artificial fertilization, the highest hatching rate of sac fry (71·35%) was found in sperm collected into immobilizing solution. The application of immobilizing solution significantly increased the number of sac fry at the levelsP<0·1 andP<0·01, if compared with intact sperm stored for 3 h and fresh sperm, res

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00609.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.Feeding trials with juvenileColossoma macropomumCuvier (approximately 40g) were carried out to study their protein requirements and their efficiency in metabolizing vegetable protein. Two groups of diets were used. In one group, the crude protein consisted exclusively of fish protein concentrate. In the second group the protein consisted of a mixture (55:45) of vegetable and animal protein without fish meal. In each group 30 and 50% protein levels were used. The highest weight increase (1·64%/day) and the lowest feeding rate were obtained with the 50% protein fish meal free diet. During the trial all fish accumulated visceral fat while body protein content decreased and dry matter increased. There was a high correlation between liver weight and liver glycogen. The highest amounts of liver glycogen were induced by diets containing fish meal and/or low protein content. In contrast lo visceral fat deposits, accumulated liver glycogen was of less significance for surviving starvation periods. The activity of digestive enzymes depends on both stomach and gut fullness. Trypsin activity, contrary to pepsin, was correlated with diet protein content, a‐amylase activity was not correlated with diet compositi

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00610.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.In turbot,Scophthalmus maximus(L.), daily examination of broodstock females should be a hatchery management practice in terms of fry output. Eggs expelled shortly after ovulation by systematic stripping of females five times a week had high viability (72%) compared to eggs collected twice a week (46%), while handling frequency did not have any effect on female fecundity (total number of ovulated eggs per kg of female). Increase of stripping frequency raised hatching rates and larva production respectively from 11% to 35% and from 20000 to 65000 larvae/kg of spawning female. The enhancement of egg quality and of the resulting larva production are discussed.

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00611.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.The effect of four environmental conditions was investigated upon sperm output in turbot,Scophthalmus maximus(L.), submitted to three different rhythms of stripping. Males kept under a natural light cycle and under a 6‐month contracted light programme released a similar sperm output in terms of total volume of semen produced per fish during the experimental period (4·9 ± 0·9ml), mean sperm concentration (29·4 ± 2·8 × 109spermatozoa/ml) and total sperm number (163·2 ± 40·5 × 109spermatozoa). Attempts to stimulate spermiation for a second time just after the end of the natural reproduction period resulted in the release of low sperm output (total volume of semen: 1·6 ± 0·4 ml; mean sperm motility: 2 min 36s ± 0 min 47s; mean sperm concentration: 47·6 ± 10·2 × 109spermatozoa/ml; total sperm number: 84·5 ± 25·3 × 109spermatozoa). Stripping frequency had no effect on total volume of semen, mean sperm motility and total sperm number. Monthly collection did not modify sperm samples in relation to stripping rank. However, decreasing volume, motility and sperm concentration were observed when males were stripped fortnightly and weekly. During the natural spawning period, the presence of females in the tank enhanced mean sperm motility (from 3 min 27s + 0 min 52s t

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00612.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.In July and August 1980–1987, mark‐recapture experiments with noble crayfish,Astacus astacusL., were performed to estimate density in Lake Steinsfjorden, south‐east Norway. Recapture rates were examined for variation according to sex, length, sampling method or length of recovery period, i.e. the time between release and recapture. Lake Steinsfjorden supports a dense, heavily exploited population of noble crayfish with few large individuals.Recapture rates did not vary with sex, but were significantly lower among crayfish smaller than 90mm total length than for larger crayfish. Different sampling methods (baited traps and scuba) prior to marking did not influence the rate of recapture (in baited traps). When the recovery period was increased from 2 to 4 days, the recapture rate increased two‐ to threefold, but a further increase in the recovery period to 4–6 days did not increase the recapture rate.The estimated density of noble crayfish varied between 013 and 036 individuals 5 70 mm total length per m2(95% CL. varied from 84

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00613.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY