摘要:

Abstract.Budgeting techniques are used to estimate the profitability of establishing commercial yabbie,Cherax destructorClark, farms of various sizes in Australia. While commercial yabbie fanning is potentially profitable, returns are very sensitive to the production level achieved and the price obtained. These parameters are uncertain, implying that the development of a commercial yabbie farm is a risky investment. Profitability increases as farm size increases from 5 to 20 ha. However, the optimum farm size is not known. Areas in which additional research into the aquaculture of the yabbie may generate large economic benefits are identified.

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1988.tb00582.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.Fry ofCichlasoma urophthalmusGünther were exposed to various concentrations of the organophosphate pesticide Trichlorfon, ranging from 1·25 to 80 mg/l in laboratory conditions. Mortality reached 100% in the highest concentrations (60 and 80 mg/l) in the first 24h. The intermediate concentration (40 mg/l) resulted in 50% mortality after 24h, and no mortality was observed in lower levels of the pesticide. LC50 at 24, 48 and 72h were 26·5, 23·7 and 17·2 mg/l respectively.Some of the surviving fish were transferred to clean fresh water for a post‐treatment growth trial. All the fish grew well with no apparent adverse effects as judged by their growth indices after 8

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1988.tb00583.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.A simple trial is described to determine the effects of brown fish meal, solvent extracted soybean meal, raw wheat meal, raw starch and dextrin on diet digestibility in juveniles of the Mexican cichlid,Cichlasoma urophthalmus(Gümher). The effects of possible anti‐nutrients in the feedstuffs used were assessed with the purpose of designing practical diets. The results did not show any effect attributable to anti‐nutrients, but showed that high dietary fibre levels reduced digestibility. The carbohydrates of soybean meal were poorly digested compared with the other sources utilized. These results suggest that the substitution of fish meal by soybean meat and other plant proteins could be increased to reduce costs of practical diets for this spe

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1988.tb00584.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.The possibility of using eels from intensive rearing ponds to restock natural basins has been investigated by comparing growth, survival and rate of yellow‐to‐silver metamorphosis of ‘wild type’ eels and of eels from an intensive rearing pond. A total of 2243 marked eels were released into a closed natural environment of 22ha; 1254 were wild type (average length 45·6 ± 9·0cm), and 989 from an intensive rearing pond, split by a mechanical grader in two groups. The first group was made of 617 well‐growing eels (44·9 ± 3·0cm), the second one of 372 smaller eels (36·9 ± 4·3cm) which had not adapted to the artificial conditions.The starting size being equal the animals grew to the same extent; in some cases the animals previously adapted to the artificial pond grew better than the wild type. The rate of metamorphosis from yellow to silver eel was 28·4% for the wild type eels and 22% for the others, although the latter became mostly silver males. Survival of the wild type eels (starting with the 35‐cm size class and covering the period from April to December) was calculated by mark‐recapture at approximately 98·6%. For the eels previously well adapted to the intensive rearing pond it was only 85%, indicating some difficulty in competing in the natural environment. The good growth shown by the smaller eels, with a survival of about 90%, would seem to indicate that these animals might be effectively used for restocking purposes, thus favouring an integration between the intensive ponds and th

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1988.tb00585.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.Sampling was carried out at 93 sites on the River Severn, England and at 8 sites on the River Dee, Wales. The age structure of the population shifted gradually from the younger to the older age‐classes with distance upstream. This was related to the time required for the eels to reach these regions and to the increase in the proportion of females.In the Severn, eels can migrate (unaided by tidal transport) at rates of between 20 and 30 km year−1, while in the Dee, passage upstream is between 10 and 20 km year−1. It is suggested that this slower rate is related to a more arduous migration, resulting from the steeper gradient of the Dee, In the lower reaches of the Severn, eels aged from 7 to 8 years were generally the most abundant, while in the middle and upper reaches, eels aged 13 years occurred most frequently and in the greatest numbers.The age structures of the populations were classified usingtwinspaninto three main groups and related to distance, upstream of the region of flow reversal, using discriminant analysis. The analysis demonstrated that age structure was related to the distance upstream of the region of flow reversal and that 60–76% of thetwinspansite groupings could be classified in terms of d

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1988.tb00586.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.The occurrence and abundance of eels were investigated in five lowland reservoirs in south‐eastern Sri Lanka. Paired fyke nets and longlines were used for sampling eels. Two tropical species of eel.Anguilla bicolorMcClelland andAnguilla nebulosaMcClelland, were caught. In two of the five reservoirs investigated onlyA. bicolorwas found and in another two reservoirs both species were caught. Eels seemed to be absent from one reservoir. The CPUE in reservoirs with eel was between 0·13 and 2·60 eels of both species per fyke net and night, and the total weight was between 81 and 814g. A small capture‐recapture experiment in Badagiriya, where eels seemed to be most plenliful, gave a population estimate of only six eels or 1·2 kg per ha (eels longer than 40cm). Such a low abundance was regarded as unrealistic. Stocks of eel could presumably, at least in some reservoirs, withstand commercial exploitation but more information is needed on recruitment, growth and migration before any advice can be given on the management of

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1988.tb00587.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.In this study we aged eels,Anguilla anguilla(L.), from a pond in the Netherlands stocked with elvers in 1966. Yellow eels were sampled from the pond in 1981. Burning and cracking the otoliths of these eels gave the expected age (15 years) in 27% of the cases, with a mean estimated age of 12·3 years. As some immigration of young eels into the pond must have occurred after stocking, the percentage of correctly determined specimens is even higher. Clearing the otoliths in ethanol was not a good method for these eels, giving a mean estimated age of 7·7 years and no age over 10 years. The use of the burning and cracking technique is recommende

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1988.tb00588.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.Eel research in Japan focuses on eel farming. The high research potential which supported the growth of the eel industry during the 1970s was transferred to other aquacultural activities around 1980, as eel production reached near saturation level. Nevertheless, research in this field is still very active and its results are of great interest in Europe as eel farming develops.A selected bibliography presents an illustration of eel research in Japan.

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1988.tb00589.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY