摘要:

Abstract.Phenotypic and genetic parameters of body and compositional traits were estimated for a population consisting of 327 two‐year‐old Arctic charr,Salvelinus alpinus(L.), from 21 full‐sib groups. Heritability estimates for body traits, such as fork length, gutted weight, condition factor and visceral weight, were all of intermediate magnitude (0·24–0·45). Heritabilities for carcass component traits, e.g. fat, protein, dry matter and astaxanthin contents, were low to medium (0·0–0·28). Genetic and phenotypic correlations were high between astaxanthin content and body traits, whereas they were medium to low between astaxanthin content and carcass compositional traits such as fat, dry matter and protein contents. The genetic variation in fat and dry matter contents was closely associated with variation in body weight. Selection for higher body weight at 2 years will probably lead to small, but positive, correlated changes in fat content. Our findings suggest that it should be possible to select for higher astaxanthin content in Artic charr to improve their fle

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00732.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Optimal illumination levels for feeding vary in different fish larvae according to feeding strategy, prey type and habitat. Determining optimal illumination conditions is important in aquaculture, as illumination seems to be the dominating factor affecting the distribution of many pelagic fish larvae. Cod,Gadus morhuaL., plaice,Pleuronectes platessaL., and turbot,Scophthalmus maximus(L.), have all been considered for aquaculture, and have different vertical positioning strategies. Three parallel groups of larvae of each of these species were exposed to planktonic feed organisms at seven illumination levels ranging from darkness to 10 800 lux. The number of ingested organisms was counted. Cod had maximal feed uptake at 1·0 lux, and higher uptake at 0·1 lux than at 87 lux. Plaice reached a threshold level at 87 lux, and turbot at 860 lux. Cod larvae, which are slowly searching dusk/ dawn predators, preferred very low illumination levels. Plaice larvae, being constant swimmers with a vertically orientated behaviour, fed equally well over a wide illumination range. The near‐surface‐feeding turbot larvae preferred high illumination l

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00733.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.For determination of ploidy levels in bivalves, three techniques are now routinely used: karyological determination, microfluorimetry and flow cytometry. This paper proposes an alternative technique which is based on determination of the optical density (OD) of stained nuclei using image analysis. A karyological and image analysis comparative experiment conducted on juveniles ofCrassostrea gigas(Thunberg) andRuditapes philippinarum(Adam&Reeve) is described and highlights the advantages of the image analysis technique. Initially developed onC. gigasandR. philippinarum, the image analysis method was easily extended to other bivalve species and to different developmental stages, as demonstrated by two experiments conducted onOstrea edulis(L.). First, percentage of triploids was consistent from the D‐larval to the adult stage of development, despite the use of different preparation techniques depending on the stage examined. Second, a rise in ploidy percentage demonstrated a differential mortality between diploid and triploid animals. Image analysis techniques are cheaper than flow cytometry but more expensive than microfluorimetry. However, image analysis equipment can also be used for algae, eggs and spermatozoa counting, and other purposes such as fluorescence measurements, analysis of autoradiographs and electrophorcsis gels, and measurement of immuno‐histochemical reacti

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00734.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.A novel method using 6‐dimethylaminopurine (6‐DMAP) has recently been demonstrated to be a good triploid inductor for bivalve molluscs. The effects of 6‐DMAP concentration, timing of treatment after fertilization, and treatment duration on survival and triploid induction ofCrassostrea gigas(Thunberg) embryos were examined. An influence of sperm concentration was also detected and discussed. Survival to D‐stage was inversely related to 6‐DMAP concentration and the percentage of triploids was shown to be 6‐DMAP dose dependent. Two optimal moments for treatment application were determined, corresponding to extrusions of the first and second polar bodies. Optimal treatment of 450μmol/1 6‐DMAP beginning 15min after fertilization over a 10min period yielded mean survival to D‐stage of 64% with a mean of 85% triploid production. As a comparison, a sample treated with 1 mg/1 of cytochalasin B (CB), 20 min after fertilization over a 15 min period, yielded a mean survival to D‐stage of only 36% with a mean of 95% triploid production. The advantages of 6‐DMAP over CB are clearly identified: this chemical is not carcinogenic, cheaper than cytochalasin B and much easier to use as

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00735.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.The study includes mating and spawning data of freshwater crayfish,Austropotamobius pallipesLereboullet, obtained in four consecutive years (1987–1990). A total number of 586 wild‐caught femaleA. pallipesin the 21·65 mm to 45·60mm carapace length (CL) size were held under laboratory conditions at different dates in September–October. Initial densities at mating time were 21 and 24 crayfish/m2with a 1:2 male:female ratio. High percentages of mating were obtained (97·4–100%) except in 1989 (57·5%). In all years, most of the matings (90%) were concentrated in a period of 8–12 days with mean water temperatures between 12°C and 13·5°C. Spawning took place a few days after mating (minimum 2 days, maximum 14 days) at mean water temperatures between 8·2°C and 10·8°C. In the first 3 years, almost 100% of mated females spawned. However, in the fourth year (1990), when the mean size of crayfish was smaller, only 72·4% of mated females spawned. The mean number of pleopodal eggs was 64 (maximum 220, minimum 18). Egg diameter ranged between 2·30 and 3·25 mm (mean value 2·78 mm). Pleopodal egg number was positively correlated with c

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00736.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.The application of different combinations and levels of pellet formulated feed and chicken manure to ponds stocked withMacrobrachium rosenbergii(de Man) did not result in any significant differences in water quality, sediment chemistry, or benthic macroinvertebrate populations. Water chemistry data indicated that all ponds were eutrophic. Chlorophyll was strongly correlated with total nitrogen, but not with total phosphorus, suggesting that nitrogen limited algal biomass. There was evidence that added organic matter was rapidly decomposed and mineralized. The sediments appeared to act alternately as sources and sinks of nutrients, although there was least variation in sediment nutrient levels in the treatment which received manure only. Applied pelleted feed was directly consumed by the prawns. In the absence of pelleted feeds, macrobenthos appeared to limit prawn growth after 1 month of culture. Simple nutrient mass‐balance equations indicated that the losses of nitrogen, phosphorus and carbon from the treatments receiving feed were not dissimilar to previously reported values in finfish cultur

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00737.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Red porgies,Pagrus pagrusL., of 70g were reared under self‐feeding conditions in six successive compartments of the same raceway and their biological performance was studied in relation to their positioning in the raceway and the quantity of water needed to produce 1kg of fish. Daily gain of biomass was found to be similar in the first four compartments, and began decreasing in the fifth and sixth. The critical water quantity, below which biological performance was impaired, was 400 m3/kg of fish. No differences in mortality rate were observed between groups. The different biological performances were associated with the impaired feeding rates and conversion efficiency observed with groups A5and A6. Results are compared with those of other species and are discussed in relation to the importance of this species for fish culture and the most appropriate technology for its productio

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00738.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Six groups of tropical freshwater catfish,Mystus nemurus(Cuvier&Valenciennes)(mean weight. 20·45 ± l·5g), were reared in 0·34m3fibreglass tanks at different stocking densities (105, 195, 285, 375, 465 and 555 specimens/m3water) for 84 days. The objective of the study was to determine the effect of various stocking densities on the growth, nutrition, biochemical composition and survival ofM. nemurus.The lowest growth rate appeared in fish at the highest density and the highest was observed in fish stocked in moderate density of 285 and 375 fish/m3water. Fish production was also lower at relatively low stocking densities of 105 and 195 fish/m3. Food conversion ratio (FCR), protein efficiency ratio (PER) and biochemical composition ofM. nemurusindicate that there exists an optimum stocking density which lies between 285 and 375 fish

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00739.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00740.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Book reviewed in this article:Aquaculture Training Manual(2nd edition). By DonaldR. Swift.On the Dynamics of Exploited Fish Populations. By R.J.H. Beverton&S.J. Holt.Genetics for Fish Hatchery Managers(2nd edition). By Tave.

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00741.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY