摘要:

AbstractExtracellular‐enzyme activity (i.e. external to cytoplasmic membranes) increased in water flowing through trout farms. Directly counted bacteria also increased, but partitioning of extracellular‐enzyme activity in outflow water by 0.2 μm filtration showed that a substantial proportion was often free rather than cell‐associated, and might have originated as free enzymes released by enriched sediments or by fish. Discharges from four trout farms caused marked increases in extracellular‐enzyme activity along a 13‐km length of river, which were sometimes sufficient to swamp native enzyme activity. The pollutant enzymes might have facilitated bio‐purification in the river. Artificially increased extracellular‐enzyme activity in the river was accompanied by increase in bacterioplankton and phytoplankton chlorophyll, but partitioning showed that most of the increases in leucine aminopeptidase and phosphatase activity were due to free enzymes. In contrast, increase in β‐glucosidase activity was perhaps more associated with bacterial a

ISSN:1355-557X    

DOI:10.1046/j.1365-2109.1996.t01-1-00818.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractEels cultured in recirculation systems are regularly confronted with high concentrations of nitrite, a well‐known toxicant for fish. In this study, the acute toxicity of nitrite to European eel,Anguilla anguilla(L.), was assessed by determination of a 96‐hLC50. The 96‐hLC50measured for eels was 143.7 ± 2.3 gm‐3NO2‐N (mean SD), which is high compared with theLC50for other fish species.The sublethal effects of nitrite on growth and feed utilization were evaluated in a feeding trial lasting 77 days, divided into an acclimation period and two experimental periods. Eels of 24 g on average were divided over 20 aquaria, connected to five separate recirculation systems. In each system, the desired nitrite concentration level was maintained by water suppletion and continuous addition of NaNO2. Fish were continuously exposed to levels of 0, 1, 5, 10 or 20 g m‐3NO2‐N. Half of the experimental groups were fedad libitumto study effects on feed intake, while the other half were fed a restricted ration to study effects on feed utilization. At the start and end of each experimental period, nitrite in the blood plasma, haemoglobin and methaemoglobin were measured. Fish weight and body composition were used to calculate specific growth rate and conversion efficiencies.In the range of concentrations studied, no significant effect of nitrite on maximum growth rate or feed utilization could be demonstrated. At the start of the experiment, low concentrations of nitrite were detected in the blood plasma, which suggests an ability of the eel to adapt to environmental nitrite. Nitrite, in the range normally encountered in intensive eel farms (max. 15 g m‐3NO2‐N), can therefore be considered a factor of l

ISSN:1355-557X    

DOI:10.1046/j.1365-2109.1996.t01-1-00820.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractA study of the environmental effects associated with the trestle cultivation of Pacific oysters,Crassostrea gigasThunberg, was conducted at a commercial cultivation site in the River Exe estuary, Devon, England. Small, but significant, changes were detected in the macrofaunal community sampled beneath oyster trestles compared with that found in adjacent uncultivated areas. These changes were associated with an increase in organic and silt composition and a reduction in the depth of the oxygenated layer of the sediment beneath the trestles. Water velocity was decreased by the presence of the trestles which probably led to the increase in sedimentation rate observed beneath them. Although biological and physical changes were observed, they were relatively minor compared with the extreme environmental changes associated with the suspended culture techniques used for other bivalve species and fishes. However, other studies suggest that the environmental effects associated with oyster cultivation become more severe in areas of large‐scale (hectares) cultivatio

ISSN:1355-557X    

DOI:10.1046/j.1365-2109.1996.t01-1-00821.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe oxygen consumption (02) and ammonia excretion (N) of juvenile and adult common wolffish was measured in culture tanks in the laboratory. The oxygen consumption and ammonia excretion were affected by temperature (C), fish size and feeding rate. For juveniles (0.5 kg; 7C) the diel oxygen consumption rate varied between 37 and 62 mg O2kg‐1h‐1and ammonia excretion between 2.3 and 5.7 mg N kg‐1h‐1. The corresponding rates for adult fish (6.9 kg; 7C) were 29‐44 mg O2kg‐1h‐1and 1.2–3.1 mg N kg‐1h‐1. The weight‐specific oxygen consumption (mg O2kg‐1h‐1) was described by the following formulae: O2(7C) = 0.17* W0.83and O2(12C) = 0.39 * W0.73and the corresponding ammonia excretion (mg N kg‐1h‐1) by: N(7C) = 0.024 W0.75and N(12C) = 0.073 W0.60

ISSN:1355-557X    

DOI:10.1046/j.1365-2109.1996.00803.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractUsing twice‐monthly application of rockphosphate (100 kg ha‐1) and a fixed stocking density (16 000 ha‐1), the influence of the application of rockphosphate on varying ratios (1:0; 1:1; 1:3) between surface feeders (catla, silver carp and rohu) and bottom grazers (mrigal, common carp and puntius) was examined in six carp polyculture ponds. Two control ponds without rockphosphate treatment with the ratio of 1:1 were used. Water and sediment quality parameters were monitored fortnightly. Maximum fish production and primary productivity were observed in the 1:3 system, followed by 1:1 and 1:0 in the rockphosphate treatments, whereas lowest values were in the control. It is suggested that manipulation in the stocking ratio between surface feeders and bottom grazers in the carp polyculture system might be a useful strategy for utilizing rockphosphate as a direct source of P ferti

ISSN:1355-557X    

DOI:10.1046/j.1365-2109.1996.t01-1-00806.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractEmpirical data on ammonia excretion rates were compiled from several published and unpublished growth studies on post‐smolt Atlantic salmon,Salmo salarL. Fish in all studies were fed to satiation with commercially produced high‐energy diets (ME = 18–19 MJ kg‐1) with a protein content of 40–45%. About 35 ± 3% (mean SE) of the nitrogen supplied to fish was excreted as total ammonia (TAN = NH3‐N + NH4+‐N). The results of a linear regression analysis of N intake to N excretion demonstrated, however, that TAN excretion rates could be divided into two components:TANexcretion[g N kg fish‐1day‐1] = 0.036 + 0.26 Nintake[g N kg fish‐1day‐1].The intercept of the regression equation indicates that the endogenous TAN excretion rates in post‐smolts could be estimated as 36 mg TAN kg fish‐1day‐1, and about 26% of the nitrogen supplied to the fish was excreted postprandially. This postprandial TAN excretion was lower than that from other salmonid species fed low‐energy diets. The daily maximum TAN excretion rate was about 43% higher than daily mean values, which agree with several studies. The ammonia quotient (A.Q.) measured was independent of the nitrogen supplied, and was calculated as 0.112. The outputs from the present model were compared to those from

ISSN:1355-557X    

DOI:10.1046/j.1365-2109.1996.00826.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractTo assess potential competition for food with indigenous species prior to their release into reservoirs in north‐eastern Brazil, the diet of hybrid red tilapia,Oreochromis niloticus O. mossambicus, maintained without supplementary feed in monocultures in freshwater ponds, was studied. The stomach contents of 160 fish (140–220 mm total length), collected monthly from February to September 1993, were analysed. Fish of all size categories were found to be phytoplanktivores. A total of 40 microalgal species were observed in the stomach contents (17 species of Chlorophyceae, 11 species of Bacillariophyceae, eight species of Cyanophyceae, three species of Chrysophyceae and one of Euglenophyceae), together with a few rotifers and some organic material. In terms of cell numbers, the overall composition of the diet was 70% Chlorophyceae, 21% Bacillariophyceae, 3% Chrysophyceae, 2% Cyanophyceae, 1% Euglenophyceae and 3% organic matter. Neither diet composition nor stomach fullness varied with fish size. However, fish had relatively fuller stomachs, with higher proportions of Chlorophyceae, Bacillariophyceae and Cyanophyceae, during the rainy season. Hybrid red tilapia appear unlikely to compete for food with a native species and so may have a role in aquaculture or for deliberate release into reservoirs in north‐eastern B

ISSN:1355-557X    

DOI:10.1046/j.1365-2109.1996.t01-1-00812.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

ISSN:1355-557X    

DOI:10.1046/j.1365-2109.1996.t01-1-00817.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY