摘要:

AbstractIntensive marine and brackishwater shrimp farms commonly use large quantities of zeolites in ponds with the aim of removing ammonia through ion exchange, providing physical cover over sediments to prevent leaching of metabolites into the water column, removing suspended solids, and improving water colour and diatom blooms. Zeolites have the capacity to remove ammonia and other nutrients/ metabolites from fresh waters by ion exchange and absorption. However, there are doubts as to their efficacy and cost‐effectiveness in saline waters. This research was conducted to investigate the effect of zeolites on water quality under a range of conditions in seven laboratory‐based trials and one pond trial. These investigated the effects of six types of commercially available zeolites and three other alumino‐silicate clays at levels from one to 26 times the recommended dose rate (380 kg ha‐1month‐1) in water at salinities of 0‐30%o for periods of 3‐19 days. The results indicated that none of the zeolites or natural alumino‐silicate clays from Thailand had any significant effects on the removal of nutrients from water at salinities of 0‐30%. Neither were these able to prevent nutrient emission from shrimp pond sediments in water at 20‐2l%o salinity. Furthermore, none of the other suggested functions of reducing levels of particulate nutrients, enhancing algal biomass, or affecting oxygen and pH dynamics were evident. This study could not establish any useful, cost‐effective role for zeolites i

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1996.tb01257.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe migration patterns of wild and released farmed Atlantic salmon,Salmo salarL., were studied by radio‐telemetry during migration from entering a river to after spawning. The wild salmon were caught during return migration in bagnets and the farmed salmon were produced in a near by fish farm. Both groups were tagged and released at sea near the river mouth of the River Alta, North Norway. A pronounced individual variation in migration pattern was observed. No significant differences was found between wild and farmed salmon in the distance from entering the river mouth to the place of the first stop (recorded in the same pool for 5 days or longer) and the days from entering the river mouth to arrival at the first stop. For both wild and farmed salmon, mean migration speed was 2.6 km day1, varying from 0.4 to 11.0 km day‐1. A larger proportion of farmed salmon distributed to the upper part of the river at spawning; mean distances from the river mouth were 30.1 and 19.1 km. respectively. Farmed salmon spent a significantly longer time from entering the river to reaching the area occupied during spawn

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1996.tb01258.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe aetiological agents of the abdominal swelling affecting farmed larvae of gilt‐head seabream,Sparus aurataL., were studied. FourVibriostrains were isolated from larvae ofS. aurataaffected by this disease, and all strains reproduced the disease in healthy larvae under controlled infection experiments, producing a significant increase of the mortality rates compared to the control (non‐inoculated larvae). Several enzymatic properties, which can act as .virulence factors, were demonstrated both in the extracellular products (ECPs) and In live cells of the strains tested. Histopathological examinations of the infected fish larvae revealed important changes of the anterior intestine and liver characterized by a marked hyperthrophy of the intestinal epithelium and hepatocytes, and by a separation of the mucosal and submucosal layers in the digestive tube. These histological alterations were associated with the constant presence of cocobacillar bacteria in the anterior intestine and in the liver. However, the precise pathogenic mechanisms of the strains tested have not been completely elucidated

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1996.tb01259.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractEarly life history traits of fish are very variable as a result of both genetic and environmental factors. In this study, we examine individual variation in early life history traits in progeny of seven females crossed with one male rainbow trout,Oncorhynchus mykiss(Walbaum). Individual eggs were followed from fertilization through hatching until death of the larvae by starvation. Larvae and yolksac size (size was shown to be a good indicator of energy content) increased with increasing egg size, but there were still differences between families after variation in egg size was accounted for. Incubation time was not correlated with egg size, and did not differ between families. The progeny from the different families utilized the available energy differently, as both longevity and growth‐rate without food was independent of yolk‐sac size, but strongly dependent on family. The observed between‐family differences in early life history traits in rainbow trout were mainly caused by genetically based effects; egg size and thus probably egg quality, which differed strongly bet ween females, could not adequately explain these differ

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1996.tb01260.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractFive diets were formulated to investigate the effects of substituting wheat flour and soybean meal with various inclusion levels of seaweed(Gracilariasp.) meal on the diet stability, performance and carcass composition of juvenile shrimpPenaeus monodonFabricius.Gracilariameal inclusion levels from 5% to 30% were tested against a control (0% seaweed) in isonitrogenous, isoenergetic diets fed for 60 days to quadruplicate groups of shrimp held in laboratory brackishwater recirculation system.Diets containingGracilariameal at up to 10% inclusion had no significant effects on diet water stability (after 12 h), shrimp performance or carcass composition compared with the control diet lacking seaweed. Diets containing 0‐15%Gracilariameal remained>88% water stable after 12 h, shrimp specific growth rates (SGRs) were 7.9‐8.0% wet body weight day‐1. survival was 48‐56%, food conversion ratios were 3.1‐3.5, and final carcass lipid levels were 6.8‐7.5%. The 30% inclusion levels ofGracilariameal resulted in a significant deterioration in diet water stability (86% after 12 h), shrimp growth (SGR 7.3% wet body weight day‐1) and carcass lipid level (4.1%). It is suggested that with the low cost and increasing availability ofGracilaria,it may be a suitable ingredient for low‐level inclusion into formulated diets for shrimp culture. The possibility of using seaweed meals for this purpose is discussed with regard to diversifying the market for cultured seaweeds and enhancing the integration of seaweed culture into coastal aqua

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1996.tb01261.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractA landlocked heliothermic marine basin (Norwegian oyster‐poll) used as a food production system for a bivalve upwelling nursery was manipulated in order to enhance bivalve production. The manipulations included artificial fertilization, reduction in brackish surface layer, increased supply of water to the bivalve nursery, increased turbulence in the poll by pumping of water and renewal of the poll water. Effects of the manipulations were investigated in a full‐scale field experiment comparing data from two monitoring programmes in 1989 and 1990. Manipulations were performed in 1990, but only traditional management was carried out in 1989, which was considered as the control. The bivalve production of 6 t live weight represented a six‐fold increase caused by the manipulations. The higher production was mainly a result of the enhanced availability of nutrients which increased primary production and enhanced availability of food for the cultivated bivalves. The manipulations drastically reduced hydrographical stratification and produced temperatures of 18‐21°C. Increased oxygen concentration and pH provided improved water quality for the cultured bivalves. Diatoms became dominant and the dinoflagellates were reduced. The manipulations could be a general aid to the management of polls and similar systems in their application as food production systems in aqu

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1996.tb01262.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractCulture water and various tissues from carps (Catla catla(Hamilton),Labeo rohita(Hamilton),Cirrhinus mrigala(Hamilton) andCyprinus carpioL., respectively) grown in an aquaculture pond in Tiruchirappalli, India, were examined for the presence of Enterobacteriaceae. Bacterial species isolated from the intestinal tract of the four fish species were similar to those isolated from the pond water. More than 50% of the total bacterial population identified in both the pond water and fishes intestinal tract wereEscherichia coliandPseudomonas aeruginosa.The presence of these bacteria suggests the need for following strict hygiene during handling and processing fish to prevent the transfer of potentially pathogenic bacteria to humans. Additionally, it stresses the need for a code of practice for fish growers in aquaculture systems for safety reasons.

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1996.tb01263.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractOlfactory attractiveness and gustatory palatability of different materials of potential importance in first‐feeding of young eels,Anguilla anguilla(L.), were examined using a novel electromechanical device which was developed for rapid screening. Comparisons were made between non‐feeding glass eels and elvers that had commenced feeding on a commercial formulated granule diet. Preparations of tubificid worms, earthworms (Eisenia foetida), cod roe, beef liver and potentially stimulatory chemicals were tested. Invertebrate‐derived foodstuffs and combinations of amino acids, inosine 5′‐monophosphate and glycine betaine were found to be more attractive than vertebrate foodstuffs pre‐weaning. Attractiveness and palatability, especially of granules formulated for eels, were strongly influenced by learning after feeding had commenced. Implications for weaning of glass eels in aquaculture are discussed. Further uses of the rapid‐screening device

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1996.tb01264.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Book review in this article:Principles of Aquaculture. By R. R. Stickney. John Wiley&Sons Ltd, Chichester.

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1996.tb01265.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY