摘要:

AbstractTwelve production trials were analysed retrospectively, covering three different rearing methods in which Nile tilapia,Oreochromis niloticus(L.), were fed with combinations or cottonseed cake and brewery waste. Highest extrapolated net pond productions, including tilapia recruits, were obtained in tilapia fingerling rearing (W0<10 g; 11.8 t ha−1year−1). Stocking African catfish, as police‐fish (0.2 catfish m−2) in mixed tilapia (W0>90 g) culture was effective in controlling tilapia recruitment, but net pond production was low (4.1 t ha−1year−1). Hand‐sexing of male tilapias (W0>90 g) only limited recruitment but resulted in a significantly higher net pond production (8.6 t ha−1year−1) than in mixed culture. Extrapolated marketable production in the treatment stocked with hand‐sexed tilapia males (tilapia only) was also higher than the extrapolated marketable production in the mixed culture treatment (tilapia and catfish combined), although this difference was not significant. Extrapolated net pond production and extrapolated net tilapia production were both significantly correlated to the daily feeding rate of cottonseed cake but not to the daily feeding rate of brewery waste. The high relative FCRs of the feed mixture were probably due t

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1995.tb00863.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractAn experiment was conducted with tilapia‐catfish polyculture at the Lagdo Fisheries Station in northern Cameroon. The objectives were: 1. To estimate the effect of supplementary cottonseed cake on net pond production in ponds already receiving dried cattle manure as basic treatment: and 2. To study the performance of African catfish,Clarias gariepinus(Burchell). in recruitment control of Nile tilapia,Oreochromis niloticus(L.). Recruitment control is essential in obtaining large tilapia sizes demanded in the market. Cottonseed cake, the most important agricultural by‐product in the region, is expensive. Dried cattle manure may be collected free from corrals deserted by pastoral ethnic groups.Three treatments were tested in duplo in six earthen ponds of 525 m2each; treatment A. daily application of dried cattle manure only (266 kg ha−1day−1); treatment B, daily manure + cottonseed at a nominal daily rate of 3% of tilapia biomass: treatment C, daily manure + cottonseed cake at 6% of tilapia biomass. Stocking densities per pond were 250 male Nile tilapia (mean Wo222 g), 150 female tilapia (W0=202 g), 30 ‘large’ African catfish (Wo= 198 g); and 30 ‘small’ catfish (W0= 52 g). Mean fish densities were 0.76 tilapia m−2and 0.11 catfish m−2. Application of dried manure and cottonseed cake was 6 days per week, and the culture period was 100 days. Fish were sampled every month and feeding rates were adjusted accordingly. Dissolved oxygen content and algal turbidity (Secchi disc) were measured once a week.Extrapolated net pond productions, including recruits, were: ‐0.41 ha−1year−1(treatment A); 4.8 t ha−1year−1(treatment B) and 6.5 t ha−1year−1(treatment C). Differences between treatments B and C were not significant(P< 0.05).Fertilization with dried cattle manure only (zero cottonseed cake) led to a negative net pond production in treatment A (negative net tilapia production but slightly positive net catfish production). Dried manure at the given application rate did not contribute sufficient nutrients to maintain the stocked fish biomass via enhanced natural production, while pond biomass was high for such an extensive system (manure only). Best fish growth was observed in treatment C (male tilapia, 0.9 gday−1: large catfish, 6.9 g day−1) although differences between treatments B and C were not significant. Growth of male and female was not significantly different, but growth rates of tilapia and catfish were significantly different (P< 0.05).Average yields of tilapia recruits in treatment B (1539 kg ha−1year−1) and C (1829 kg ha−1year−1) were about four times the average yield of recruits in treatment A (468 kg ha−1year−1) but differences between treatments A, B and C were not significant. It was sugcess, or the reproductive efficiency of tilapia in treatment A could have been lower as a result of that treatment. However, clouds of up‐swimming fry appeared to be at least as numerous in the replicate ponds o

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1995.tb00864.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractTwo cottonseed cake feeding strategies were tested in pond culture of hand‐sexed male Nile tilapia,Oreochromis niloticus(L.). (W0>80 g), with the objective of making better use of the algal blooms which develop when cottonseed cake is applied to a pond.In the conventional ‘progressive feeding strategy’, the daily amount of cottonseed cake was adjusted monthly for the total tilapia bioweight estimated from sampling, assuming that cottonseed cake primarily acted as a tilapia feed. In the ‘linear feeding strategy’, ponds received a fixed daily amount of cottonseed cake throughout the trial, based on the hypothesis that tilapia would cover their nutritional requirements mostly by grazing the algae.Each feeding strategy was tested at two feeding levels. Mean daily feeding rateRin the progressive feeding strategy averaged 48.6 (low feeding level) and 102.5 kg ha−1day−1(high feeding level), and 49.8 and 82.9 kg ha−1day−1in the linear feeding strategy.Significantly better growth rates and feed conversion rates were obtained in the progressive feeding strategy. Average extrapolated net pond production was highest at Rpr=6% body weight day−1(10.61 ha−1, year−1). It was concluded that cottonseed cake contributed to tilapia growth mainly directly as a tilapia feed rather than indirectly as a pond fertilizer via algal production.Finally, the appropriateness of the metabolic feeding rate Rmb(BW0.8day−1) was discussed, compared with the progressive feeding rate Rpr(%BWday−1). (BWdenotes body weight). A practical, two‐step linear feeding method was proposed for cottonseed cake as a ‘rule of thumb

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1995.tb00865.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractCatfish (meanW0189 g) were added to ponds (525 mJeach) stocked with 230 hand‐sexed, male tilapia (Wu163 g), at 0.04, 0.10 and 0.15 catfish m−2. In each pond, two female tilapias were introduced, thereby creating a sexing error of less than 1%. Feeding was fixed throughout the experiment at 2.5 kg of cottonseed cake per day per pond 6 days per week (mean feeding rateR =41 kg ha−1day‐1). Rearing time was 125 days. Average net pond production per treatment (ranging between 7.5 and 7.9 t ha−1year−1) and marketable production were not different between treatments but net tilapia production was significantly lower at the highest catfish density. Both catfish and tilapia growth were negatively correlated with catfish density due to feed competition near the end of the experiment. It was concluded that catfish efficiency in controlling tilapia recruitment was strongly reduced by the availability of supplementary high‐protein feed. Large catfish competed with the parent tilapia for the cottonseed cake but apparently did not exploit the tilapia recruits. Yield of tilapia recruits was lowest at the highest catfish fingerling density, although this was not significant. The number of catfish fingerlings was significantly higher at the lowest catfish density, which indicated that large catfish preyed on catfis

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1995.tb00866.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractFour earthen ponds (250 m2each) were stocked each with 250 small catfish (W0=39g). In treatment A, African catfish.Clarias gariepinus(Burchell), were raised in monoculture, while in treatment B catfish were raised in polyculture with an additional 125 male Nile tilapia,Oreochromis niloticus(L.) (W0=44g). Feeding of cottonseed cake was at about 4% of catfish body weight day−1. Daily feed quantities, however, were averaged over all four ponds so that each pond received the same amount of cottonseed cake. Rearing time was 118 days. In treatment A, catfish grew to an average weight of 200g. In treatment B, catfish reached 158g and tilapia 185g, Extrapolated marketable fish production was strikingly similar in all four ponds (around 4.8 t ha−1year−1). No synergistic effect was obtained by stocking microphagous tilapia, although the feeding of cottonseed cake enhanced dense algal blooms in all ponds. Catfish did not appear to exploit the tilapia recruits, as an indirect pathway of algae cro

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1995.tb00867.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe acute toxicity of alkylbenzene sulphonate (ABS) detergent to the toothed carp,Aphyosemion gairdneri(L.), was investigated using static bioassays and continuous aeration over a period of 96 h. The 96‐h LC50, opercular ventilation rates per minute and behaviourial responses were evaluated. The 96‐h LC was determined to be 25.11 ± 8.4 mg l−1. The toxicant led to an initial increase in the opercular ventilation, which then decreased below the initial values by the 96th hour of exposure. Prior to death, erratic swimming, lost of balance and respiratory distress were observed. Skin lesions and haemorrhaging of the gill filaments were observed on dea

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1995.tb00868.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractFour red tilapia hybrids were evaluated for growth in earthen ponds and for colour distribution: ‘red’O. niloticus(L.) xO. niloticus(L.) orO. aureus(Steindachner). andO. niloticusorO. aureusx ‘white’ segregate of a Philippine red tilapia (Oreochromissp.). The best growth was obtained in the ‘red’O. niloticus x O. niloticusandO. aureusx‘white’ hybrids, although they constituted only a little over 50% males. Of these two hybrids, the former is all‐red, while the latter segregates into 35% red and 65% less attractive bronze‐coloured individuals. Ways for establishing all‐male populations of these two hybrids, for possible improvement of their performance, are discussed. Incompatibility between ‘red’O. niloticusfemales andO. aureusmales, limiting fry production of this hybrid, was observed. The few fish of this hybrid obtained and tested proved t

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1995.tb00869.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractMicroflora isolated from fish intestines have been described for a limited number of salmonid fish species. The size of the microbial population of salmonids appears to vary within different regions of the gastrointestinal tract. The genera present in the gastrointestinal tract seem to be those which can survive and multiply in the intestinal tract. The predominant bacteria isolated from the salmonid gut are aerobes or facultative anaerobes. Few investigations have evaluated obligate anaerobes in the digestive tract of salmonids, and these studies have suggested that the population levels of obligate anaerobes are lower than those of facultative anaerobes. The bacterial genera isolated from fish intestines vary with salinity, antibiotics, chromic oxide, diet and dietary components such as linoleic acid, and display day‐to‐day fluctuations.Acinelobacterspp.,Enterobacter spp.andPseu‐domonasspp. are regarded as autochthonous inOncorhynchusspecies, whileAeromonasspp.,Flavobacteriumspp.,Pseudomonasspp. andLactobacillusspp. are suggested as autochthonous in Arctic charr,Salvelinus alpinu

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1995.tb00870.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe survival of salmon lice.Lepeophtheirus salmonis(Krøyer) on Arctic charr.Salvelinus alpinus(L.). in fresh water was studied. The results showed that salmon lice were able to survive for up to 3 weeks, in contrast with previous published information that the parasite is quickly shed when the fish enters fresh water

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1995.tb00871.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY