摘要:

Abstract.Fibreglass pools (3·5m diameter, 1·2m high) were evaluated as model ponds and used to compare the effects of fertilization strategies, designed to promote either phytoplankton blooms or benthic algal mats, on production ofPenaeus monodonFabricius and water quality over 8 weeks. As production results were similar to those reported from commercial ponds in Australia and Taiwan, the pools were considered appropriate experimental units for assessing pond management strategies. Large blooms of filamentous algae developed in four of the eight pools with benthic algae. In these, individual prawn growth (weight gain), biomass gain, food conversion efficiency and drain harvest efficiency were all lower (P<0·05) than in pools with phytoplankton. Abundance of filamentous algae was negatively correlated (P<0·05) with prawn weight gain (r =−0·80) and drain harvest efficiency (r =−0·76). Differences in water quality arising from alternative fertilization strategies occurred but did not explain differences in prawn production indices. The results indicate that ponds used for monoculture ofP. monodonshould be fertilized so as to stimulate and maintain phytoplankton blooms and to discourage blooms of filament

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00687.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.The African catfish,Clarias gariepinusBurchell andClarias anguillarisL., were induced to ovulate in aquaria by the administration of human chorionic gonadotropin (hCG) and pituitary extracts ofClarias albopunctatus(Nichols&Lamonte) and frog,Rana elegans.For final maturation and ovulation in both species ofClarias, the total dosage of each hormone was inversely proportional to the initial oocyte diameters of the recipient females. The time of ovulation after the last injection (latent period) was significantly shorter (11–13h) in females with large oocyte diameters (>920μm) than in those whose mean oocyte diameters were less than 920 μm (13–16h) (P<0·05). The mean dosage of each test hormone required to induce ovulation was lower in females with large oocyte diameters than in those with smaller oocyte diameters (0μ05) and was about 86%.Clarias albopunclatus and R. elegans, which are economically unimportant and abundant in Anambra River basin, Nigeria, could be used as effective sources of hypophyseal factors inClariasbreeding pr

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00688.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.In aquaculture experiments of only a few months'duration, fish can approach their asymptotic size and growth rates may change greatly. One objective of aquaculture is to obtain a maximum economic return, and a growth model is needed to relate rate of growth to food consumption and other costs to find the optimum duration of growth cycles. Von Bertalanffy's equation is an asymptotic growth model which can be used for this purpose. A variable growth rate model was developed to describe fish growth oscillations observed in aquaculture experiments. This growth model provides improved estimates of von Bertalanffy's equation in aquaculture and can be used for an efficient evaluation of fish production during production cycles.

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00689.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.The quantitative dietary ascorbic acid requirements of fingerling Nile tilapia,Oreochromis niloticusL., were assessed by feeding seven diets containing graded supplements of this vitamin (0, 50, 75, 100, 125, 300 and 400mg/100g dry diet) to triplicate groups of fish for 12 weeks. Fish fed the diet devoid of ascorbic acid exhibited significantly (P<0·01) poorer growth and higher condition factor. Food conversion and protein efficiency ratios were improved with increasing dietary ascorbic acid level up to 125mg/100g of dry diet. Protein utilization, haematocrit, haemoglobin level and tissue ascorbate concentrations were depressed in fish fed the ascorbic‐acid‐free diet. Tissue ascorbate concentrations, especially for liver, were highly correlated with dietary ascorbic acid level. Fish fed the ascorbic‐acid‐free diet exhibited deficiency signs including erratic and convulsive swimming, anorexia, lethargy, caudal fin erosion, skin haemorrhages and mortality. Based on the nutritional and pathological parameters investigated, the recommended dietary inclusion level is 125mg/100g dry diet, which is equivalent to a net requirement (after processing and storage) of 42mg/1

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00690.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Eight semi‐purified diets were formulated to investigate the effects of dietary lipid and lecithin levels on the performance and carcass composition of post‐larvalPenaeus monodonFabricius.Supplementary soyabean lecithin levels from 0 to 9% and total dietary lipid (cod liver oil:soyabean oil at a ratio of 3:1) levels from 3·5 to 12·5% at 3% increments were tested in diets that were isonitrogenous and isoenergetic. The diets were fed for 50 days to triplicate groups of post‐larvalP. monodonheld in a laboratory marine recirculated water system.Despite poor overall performance due to the purified dietary ingredients, the absence of basal lipids and/or lecithin was found to result in the poorest performance. Optimum production was obtained with a diet containing 3% basal lipid and 3% lecithin at a total lipid level of 6·5%. The addition of dietary lecithin (particulariy at 46·63% of the total lipid) at up to 3% in terms of growth, feeding efficiency and production or 6% in terms of survival significantly (P<0·05) increased shrimp production. Lecithin was therefore probably acting as a growth, survival and/or phago‐stimulant inP. monodon.The total lipid requirements are consistent with those reported by other workers for penaeid shrimp, and are probably a result of the requirement for essential fatty acids, the stimulant properties of lecithin and the calorigenic effects of high dietary

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00691.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Two experiments were carried out to study the effect ofn‐3 HUFA levels in rotifers on survival, growth, activity and fatty acid composition of gilthead bream,Sparus aurata(L.), larvae. From the third to the 15th day after hatching, gilthead bream larvae received one of the three kinds of rotifers containing different percentages ofn–3 HUFA. Moisture, crude lipid, saponifiable matter and fatty acid composition of total lipids of rotifers and larvae were determined.A good correlation was found between larval growth andn–3 HUFA levels in rotifers. Larval survival was also significantly improved by the elevation of then–3 HUFA levels in rotifers. A high occurrence of hydrops was registered in larvae fed with EFA‐deficient rotifers. Then–3 HUFA levels in the larvae were increased by the elevation ofn–3 HUFA contents in rotifers. However,n–9 fatty acids in the larvae remained almost constant, regardless of the different 18:1n–9 contents in rotifers. Therefore, the ratio of oleic acid ton–3 HUFA, known to be an indicator of the EFA deficiency in fish, was reduced by the elevation of then–3 HU

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00692.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.This paper is divided into four parts. First, history: cage culture has long been practised. The origin of cage culture world‐wide should be regarded as the middle reaches of the Yangtze River, China, in the Sung Dynasty. Second, characteristics of cage culture in China. Third, influence: development of open‐water fisheries is actively promoted in lakes, reservoirs and rivers. More kinds of water bodies have been employed for this purpose. Marine cages have also rapidly developed. Finally, discussion and conclusions. Cage culture is a modern development of aquaculture which has changed the long‐established, fish‐farming structures and, to a great extent, pushed forward fisheries development in China. Cage culture is typically characterized by intensive farming, running‐water culture, high yield and great efficiency. It is generally accepted that cage culture will actively play an increasingly important role in international aq

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00693.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.The present study attempts to investigate the effect ofPenaeus monodon‐type baculovirus (MBV) infection on growth and survival of the larval stages ofPenaeus monodonFabricius. The results showed that MBV may significantly retard larval growth and cause mortalities during the larval stage. The MBV‐infected larvae ofP. monodonvaried more in body size than uninfected control shrimp, and were discoloured. To detect the presence of MBV in larval prawn, histopathological techniques and an enzyme‐linked immunosorbent assay (elisa) were used. Positive diagnoses were routinely detected as early as the zoea 1 stage when ELISA was

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00694.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.In a feeding experiment, the metabolizability of dietary carbohydrates in diets for turbot,Scophthalmus maximus(L.), was estimated and expressed as percentage of the metabolizability of dietary lipids. Four isoenergetic and isonitrogenous dietary treatments were applied with varying percentages of non‐protein energy presented as starch. In order to obtain results allowing quantitative interpretation, an experimental design was used in which effects are reflected in varying body fat depositions only. Two methods were used simultaneously to overcome practical problems associated with differences in energy density between carbohydrates and lipids. The conventional method was based on equal feeding rates combined with the inclusion of inert filler in the diets, whereas the alternative method applied different dietary nutrient percentages in combination with different feeding rates. Although similar results were obtained, the alternative method was more convenient to use than the conventional method. Because of the experimental strategy applied, no significant effects on growth and protein utilization were obtained, but lipid deposition rates were significantly reduced at increased percentages of non‐protein energy presented as starch. The metabolizable fraction of the gross dietary carbohydrate energy was estimated as 67% of that of dietary lipids. This reduction does not indicate that turbot have any systematic deficiency in metabolizing dietary carbohydra

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00695.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.High rate of feminization was achieved by oral administration of diethylstilbestrol (DES) and ethynyloestradiol (EES) to gonadally undifferentiatedOreochromis mossambicus(L.) andO. mossambicus×O. urolepis hornorumTrewavas all‐male hybrid. All‐female groups were produced at doses>10mg/kg DES and>50mg/kg EES, when fry immediately after yolk‐sac absorption were fed hormone‐treated feedad libitum.The critical period for feminization was about one week. Treatments longer than 10 days did not result in a higher proportion of females, and treatments starting later than one week after yolk‐sac absorption were not effective. Optimal derived protocol was applied toO. aureus(Steindachner), resulting also in complete fe

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1994.tb00696.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY