摘要:

AbstractThe genetic composition of consecutive year classes of two farmed rainbow trout,Oncorhynchus mykiss(Walbaum), strains was assessed, using starch gel electrophoresis of 11 enzymes encoded by a minimum of 23 loci, many of which have been shown to be polymorphic in previous studies. Angle frequencies at the majority of polymorphic loci varied significantly between year classes of each strain. Several alleles which were present at low frequency in the 1900 year classes, were absent in the samples from the 1991 cohorts. However, mean heterozygosity per locus (H) did not differ significantly between year classes of either strain, illustrating that allelic diversity is a more sensitive indicator of loss of genetic variability than mean heterozygosity. This heterogeneity between cohorts is probably due either to broodstock maintenance practices such as the use of insufficient numbers of spawners, or, in the case of one strain, to bottlenecking caused by selection for late maturation and increased growth rate. Genetic monitoring of all year classes of reared strains is suggested, if insufficient breeding and distribution records are available from egg producers. Such records are often unavailable in commercial situations.

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1996.tb01299.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe efficiency of the rotiferBrachionus calyciflorusPallas as a nutritional source for rearing larvae was studied in a coldwater cyprinid, the gudgeonGobio gobio(L.), and in a percid, the perchPerca fluviatilisL., through their composition in fatty acids. Rotifer intake affected the fatty acid profiles of the larvae significantly, with an especially remarkable presence of the linoleic family. In gudgeon fed with rotifers, the polyunsaturated fatty acids (PUFA) reached 10.98% of the dry weight of the sample. This rate was highly influenced by the presence of the acids C18:2n‐6 and C22:6n‐3 which represented 66% of the total PUFA. In perch fed exclusively with rotifers, the PUFA represented 7.27% of the dry weight. In both cases, the ratio n‐3/n–6 decreased by 75% and 73% after 10 days of feeding with B.calyciflorus.This variation was probably due to the exogenous supply in acids of the linoleic family through the rotifers and to the fact that these two species of fish seem to favour the mobilization of the n‐3 PUFA such as C22:6n‐3 for growth and survival. Moreover, with the utilization of rotifers. the reactions of elongation and desaturation from the C18:2n‐6 and C18:1n‐9 seemed to be much more important in the larvae. Lastly, the transition from a diet based on rotifers to one made up exclusively of frozenArtemianauplii led to a significant reduction of fatty acids in fish. It reached 60.2% and 26.5% of the total fatty acids in the gudgeon and perch, respectively, and was observed especially at the level of the PUFA. On the other hand, a slight increase of the ratio n‐3/n‐6 was pointed out in the perch fed a mixed diet (co‐feeding with rotifers and dry food), a phenomenon probably due to the reduction of C

ISSN:1355-557X    

DOI:10.1046/j.1365-2109.1996.00773.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractUsing the cryopreservation method of Lahnsteiner, Berger, Weismann&Patzner (1995,Aquaculture Research26, 801‐807) the influence of allowable variations of methodical parameters (storage of semen before cryopreservation, dilution ratios in the extender, equilibration in the extender, cooling rates, storage of deep‐frozen semen in liquid nitrogen, storage of frozen/thawed semen, minimal sperm/egg ratio) was investigated under the aspect of routine utilization.Under optimized experimental conditions, fertilization rates were 90‐100% of controls inOncorhynchus mykiss(Walbaum),Salmo truttaL.f. lacustrisSalmo truttaL.f. farioandSalvelinus fontinalis(Mitchill). The following results were obtained: 1. Storage of untreated semen for more than 1 h before cryopreservation decreased the postthaw fertility. 2. Equilibration of semen up to 20 min in the extender did not affect the postthaw fertility. 3. Optimal dilution ratio of semen in the extender was threefold inOncorhynchus mykissandSalvelinus fontinalis.Lower dilution ratios decreased the postthaw fertility, higher dilution ratios did not affect the postthaw fertility. InSalmo trutta f. lacustrisandSalmo trutta f. fario, which have a higher sperm density, optimal dilution ratio of semen in the extender was fivefold to sevenfold. 4. InOncorhynchus mykiss, as inSalmo trutta f lacustrisandSalmo trutta f. fario, the optimal freezing height was at 1.5 cm above the level of liquid nitrogen (‐110 ± 2oC); inSalvelinus fontinalisit was 2.5 cm above the level of liquid nitrogen (‐92 ± 2oC). Changes in the freezing height of 0.5 cm (about 10oC) resulted in a significant decrease of postthaw fertility. 5. Storage of deep‐frozen semen for up to 370 days in liquid nitrogen had no influence on its postthaw fertilization rate. 6. Storage of frozen/thawed semen for 30 s before insemination significantly decreased its postthaw fertility. 7. Reliable minimal sperm:egg ratio to obtain fertilization rates of 90‐100% of control was 3‐5 X 105

ISSN:1355-557X    

DOI:10.1046/j.1365-2109.1996.t01-1-00774.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThree indigenous carp species,Catla catla(Ham.),Labeo rohita(Ham.) andCirrhinus mrigala(Ham.), and two exotic carp species,Cyprinus carpioL. andHypophthalmichthys molitrix(Val.), were stocked together at a total density of 6000 fish ha‐1in the ratio of 11:22:14:14:11, respectively. Three pelleted feeds, maize gluten (MG), cotton seed (CS) and fish meal (FM), were fed at 5% of the body weight of fish per day. The crude protein content of each feed was different. Growth rates for exotic species were significantly higher (P<0.05) on all feeds than growth of indigenous species. The best growth for both exotic and indigenous carps was achieved on fish meal. Supplemental feeds made from locally available materials can enhance fish culture in Pakista

ISSN:1355-557X    

DOI:10.1046/j.1365-2109.1996.t01-1-00775.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe effects of varying water depths and temperature on the growth, feed utilization, mortality rates and body composition of Nile tilapia,Oreochromis niloticus(L.), were evaluated. Triplicate groups of 20 fish (mixed‐sex) m‐3were stocked into 200‐m2freshwater earthen ponds maintaining four water depths: 50, 100, 200 and 300 cm. The fish were fed on commercial fish pellets (23% protein), twice a day for 10 months (May 1991‐February 1992). Water temperatures ranged from 5oC to 33oC.Growth performance and survival were significantly affected by pond depth and water temperature. Fish weight gain was lowest (250 g per fish), feed conversion poorest (3.15), and mortality highest (41.5%) at 50 cm depth, whereas 100‐200 cm depth produced the best growth rates at warm water temperatures (>21oC). At 100‐200 cm depth, weight gain was significantly (P<0.001) increased to 348‐362 g per fish, feed conversion improved to 2.53‐2.59 (P<0.01) and mortality reduced to 21‐27% (P<0.001). Fish growth was significantly reduced (P<0.001) below 21oC. Below 10oC, fish stopped feeding and developed severe stress, fungal infection and high mortality. However, mortality rate was significantly reduced at 300 cm depth. Body lipid and protein were sharply decreased (P<0.001) with decreasing water temperature and pond depth, whereas body ash showed i

ISSN:1355-557X    

DOI:10.1046/j.1365-2109.1996.00776.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractNaturally spawned Sydney rock oystersSaccostrea commercialis(Iredale and Roughley),were used to determine the appropriate stage of development for inducing triploidy and to compare the effectiveness of cytochalasin B (CB) and 6‐dimethylaminopurine (6‐DMAP) in dose‐optimization trials. Induction should commence at 50% first polar body (PB1) extrusion in eggs (approximately 17‐19 min post‐fertilization at 25oC). By day 5 the highest triploidy percentage and yield (number of triploid larvae per 100 fertilized eggs) were achieved in the ranges of 0.75‐1.5 mg CB 1‐1(1.6‐3.1 μmCB)or 200‐400 μm6‐DMAP (32.6‐65.3 mg 6‐DMAP l‐1). However, CB treatment resulted in greater survival and triploidy percentage than 6

ISSN:1355-557X    

DOI:10.1046/j.1365-2109.1996.t01-1-00777.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractHigher‐energy fish feeds can reduce waste discharges and might also improve water quality in recirculating fish‐culture systems. A higher‐energy diet, Zeigler Salmon High Energy feed (HE; 45% protein, 20% fat, 17.4 MJ digestible energy kg‐1) and a lower‐energy diet, Zeigler Hi‐Fat Trout Grower (LE; 38% protein, 12% fat, 14.6 MJ digestible energy kg‐1) were fedad libitumat different times to rainbow trout,Oncorhynchus mykiss(Walbaum), in a semi‐closed recirculating culture system by means of demand feeders. The system contained two 10‐m3fish‐culture tanks, each with a downstream microscreen (80 μn) filter. Feeding rates per day and per unit biomass were not significantly different between diets. In general, use of HE was associated with higher levels of total ammonia nitrogen (TAN) and NO2‐N, lower BOD5and total suspended solids (TSS), and lower effluent releases of suspended solids per unit feed, NO3‐N per unit feed, and dissolved phosphorus per unit feed. Although total effluent P per unit feed or P fed did not differ significantly between diets, HE had significantly more of the total effluent P in the settleable solids, 85% vs. 76%. Differences in water quality in the system were probably not of great importance wit

ISSN:1355-557X    

DOI:10.1046/j.1365-2109.1996.t01-1-00778.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractGrowth and survival of the Catarina scallop,Argopecten circularis(Sowerby), were determined in relation to stocking density and length of culture period. Data were analysed by means of the von Bertalanffy growth equation and the weight‐length allometric relationship. A mortality equation was empirically derived from the experimental data. Stocking density significantly affected both growth (P<0.05) and mortality parameters (P<0.01). The coefficients for the weight‐length relationship. however, were not affected by stocking density. Mortality was highly variable, both during the culture period and between the different stocking densities. Two mortality patterns were identified. One was associated with post‐spawning mortality and lower stocking rates. The other occurred at high densities where increased temperatures and overstocking provoked high mortalities and extremely divergent survival responses. The results showed that mortality, rather than growth, reflects more accurately the effects of density, and that better survival is not necessarily produced by stocking at the lowest

ISSN:1355-557X    

DOI:10.1046/j.1365-2109.1996.00779.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Book review in this article:Pike: Biology and Exploitation. Fish and Fisheries Series 19. Edited by John F. Craig Chapman and HallManual for the Isolation and Identification of Fish Bacterial Pathogens By G. N. Frerichs&S. D. Millar.Fungi and Fish Diseases By L. G. Willoughby Pisces PressSelective Breeding Programmes for Medium Sized Fish Farms. FAO Fisheries Technical Paper No. 25. By D. Tave. FAO, Rome.Fish Nutrition in Aquaculture. Chapman and Hall Aquaculture Series 1. By S. S. De Silva&T. A. Anderson. Chapman and Hall, London.

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1996.tb01307.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY