摘要:

Abstract.For the first time, effective treatments using cytochalasin B were developed to induce triploidy in the European clam,Ruditapes decussatus(L.). The percentage of triploid embryos was assessed by karyological or image analysis. Two treatments (0·5 or 1 mg of cytochatasin B (CB) per ml of dimethyisulfoxide in 1 litre of sea water) were applied at different times after fertilization (10 to 25min), for two different periods (15 and 20min). Best results were obtained for a CB concentration of 1 mg/1. When treatment was applied 15min after fertilization for a 20min period, 94% and 95% of triploid embyros were obtained in two repeated experiments. At metamorphosis, the treated larvae appeared to be no smaller than the control larvae in all experiments. However, in general, significantly higher mortalities for CB‐treated batches were found when compared with the untreated bat

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00742.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Hybridization between tilapia species, to produce all‐male broods, was at one time considered a promising method to prevent uncontrolled reproduction (Hickling 1963). It has been tested with a number of tilapia species, but most attempts at large‐scale hybrid production did not succeed. The major reason for this failure is the instability in production of all‐male hybrids. Sooner or later the system broke down, and females began to appear in increasing proportions among progenies which, up to then, had been all male. It appears that this breakdown is largely due to the infiltration of parental broodstock by individuals of a different genotype, predominantly hybrids between the two species involved, which are difficult to distinguish from their parents. This problem may be solved by a careful examination of the broodstock, often including thousands of individuals, and culling doubtful cases. It requires trained and permanent personnel. Hybridization has been largely superseded by hormonal sex inversion as a method of producing all‐male tilapias. In this paper, the two methods are considered as alternatives, if problems of broodstock purity are solved. Establishing a pilot scheme for hybrid tilapia production is reco

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00743.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.A mass balance was constructed for nutrient flow through intensive marine shrimp ponds in which budgets for nitrogen and phosphorus were determined for a series of ponds in southern Thailand over two or three culture cycles. Ninety‐five per cent of the nitrogen and 71% of the phosphorus applied to the ponds was in the form of feed and fertilizers. Of the feed input (at a food conversion ratio of 2) only 24% of the nitrogen and 13% of the phosphorus was incorporated into the shrimp harvested, whilst the remainder was retained in the pond and ultimately exported to the surrounding environment. The effluent water contained 35% of the nitrogen and 10% of the phosphorus discharged. Of the N and P exported in this effluent, 63–67% occurred during routine water exchange and the remainder during drainage on harvest. A major portion of the nitrogen (31%) and most of the phosphorus (84%) was retained in the sediments, emphasizing the importance of the correct removal and disposal of sediments between crops. Pond age (between two and six production cycles) did not markedly affect nutrient flows, whilst increasing stocking density increased the quantity of nutrients, but not their relative proportions.The results derived from the nutrient budget provide data which may help define effective management techniques for reducing potentially harmful nutrient levels within intensive shrimp ponds, and for reducing the discharge of nutrients to the local environment. The data may also assist in determining the carrying capacity of an area for shrimp farming, and the potential impact of its development on the environm

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00744.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.The possibility of improving aquaculture water quality using different kinds of zeolites is discussed. Zeolites are aluminosilicates, whose framework structure allows them to exchange cations. Cations have differing affinities for different structures, and in particular ammonia has a great affinity for phillipsite and clinoptilolite structures. These zeolites are already used for ammonia removal from municipal piggery, and aquacultural wastes. In the present paper, ammonia removal from aquacultural water from recirculating systems has been tested, comparing different zeolites under laboratory conditions. Phillipsite and clinoptilolite tuffs were effective in ammonia removal, while chabazitc tuff having a lower content of zeolitic material (50%) and lower affinity for ammonia showed that a lower temperature did not influence ion exchange capacity in any of the zeolites.

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00745.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Several investigations have used Cr2O3(chromic oxide) as an indigestible marker in digestibility studies. However, in this review the effect of chromic oxide on dietary lipid during passage through the digestive tract, and the gastrointestinal microflora in long‐term nutrition studies in Arctic charr,Salvelinus alpinus(L.), are discussed. Based on these results it is suggested that the use of chromic oxide may lead to erroneous results. Furthermore, this paper focuses on the effect of dietary linoleic add (18:2 n–6), acetate and salinity on lipid and individual fatty acid digestibilities in Arctic charr.No full studies have been carried out regarding the essential fatty acid requirement (EFA) of Arctic charr. Available data indicate that (n–3) polyunsaturated fatty acids (PUFAs) are the prime EFA, as in most other salmonids. Furthermore, quantitative EFAn requirements may be higher than the 1% dietary level described for other salmonids. Feeding (n–3) PUFAs at 1% lead to high contents of (n–9) PUFAs in the polar lipids, presently recognized as‘indicators’of EFA deficiency. Moreover, this review focuses on elongation and desaturation of short‐chain EFA to their C20C22counterparts, and the feedback inhibition

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00746.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Ammonia excretion rate of the marine bivalveTapes decussatus(L.) varied with body weight, temperature and starvation. There was a steady state in the excretion rates, in which these rates neither increased nor decreased during the first 6 days of starvation. The highest rates of ammonia excreted during the steady state (before decline to lower level) depended on the temperature (715 ± 86 and 395 ± 55 μg NH4.N/clam/h × 10−2) at 28°C and 20°C, respectively. At 16°C, the steady state extended from 6h to 18d starvation. Ammonia excretion rates were higher for starved clams than for fed clams at all sizes, e.g. clams of 0·07 g dry flesh weight (28 ± 9 and 13 ± 5 μg NH4.N/clam/h × 10−2respectively) at 16°C but not at 20°C and 28°C. At each temperature, weight‐specific ammonia excretion rates were related to dry flesh weight of starved clams but were not

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00747.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.tb00748.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.tb00749.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.tb00750.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Book reviewed in this article:Genetics and Evolution of Aquatic Organisms. Edited by A.R. Beaumont.

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00751.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY