摘要:

Abstract.These analyses of the tilapia fingerling industry in the Philippines focus on the economics of production in different hatchery systems and on fingerling marketing channels. The analyses are based on cross‐sectional data from government and private hatcheries in late 1982 and from December 1983 to March 1984.The relative profitabilities of different hatchery systems (land‐based and lake‐based) are estimated and economies of scale are analysed. Conceptual and methodological issues inherent in analyses based on cross‐sectional data are discussed in the context of the extreme difficult standardizing inputs and output from private tilapia hatcheries which are characterized by wide variation in management pr

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1987.tb00121.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract.The development of small‐scale hatcheries is placed in perspective with olher commercial methods of fish seed production, private and public, in the north‐east region of Thailand. Case studies of six small‐scale hatcheries operated by farmers in this region are presented with details of the production, costs and returns of these farms in relation to their size, location, species of fish produced, amount of capital invested and marketing and sales strategies, Rates of return were found to be favourable, with the exception of a group‐based hatchery. The relationship between the production of carp and tilapia fry. which is believed tn be incompatible under present systems, is discussed. The wider implications of the role of small‐scale hatcheries to provide fish seed for farmers in rural areas and the future of public sector involvement are c

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1987.tb00122.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract.From 25 July to 11 September 1984 Atlantic salmon,Satmo salarL., parr were observed underwater between 0800 and 1600 h, feeding actively from defended territories at two sites in the River Tilt, Perthshire, Scotland. Territories comprised one or more preferred stations on or just above the substrate, from which the fish intercepted drifting particles (75% of feeding), or foraged on the substrate (25%). Drift feeding occurred 36% at the surface, 35% in mid‐water and the remainder at the feeding station. 35% of prey particles were attacked directly from the feeding station, and 65% indirectly after preliminary inspection, sometimes involving a drift downstream by the fish. 20% of captures were made upstream of the station and 80% downstream. 12–15‐cm fish fed more frequently at the surface, while 10‐cm fish fed in mid‐water or at their stations. Surface feeding decreased proportionately during rainfall. Frequency of feeding increased with temperature. Feeding was depressed in the presence of large

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1987.tb00123.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract.Juvenile hatchery‐reared Atlantic salmon,Salmo salarL., were offered choices of pelletted or four types of wild prey (chironomid larvae, ephemeropteran nymphsEcdyanurusandBaetisand tnchopteran larvaeHydropsyche) of the same particle widths, in a test flume Preference for wild foods increased over 16 trials (1·5 h), and was greatest forEcdyonurtaandHydropsyche, which had prey width fish fork length (PFR) ratios of 0·019 and 0·022 respectively, Pelletted food was rejected sooner whenEcdyonurusnymphs were offered as the alternative food than when chironomid larvae were (P<0·05). Pret'erence (P<0·05) forEcdyonuruswas achieved after 11 trials and for chironomids after 15. The time required to capture the first prey item was two to three times as long for pellets as for wild prey and did not change with experience for any prey type. Mean capture distance did not change with experience. It is concluded that acceptability of wild prey should not limit performance of pellet‐fed salmon released into

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1987.tb00124.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract.Growth was studied in Arctic charr,Salvelinus alpinus L., from three differing loch habitats in Scotland. Otoliths were more reliable for age determination than scales. Growth rates were variable both among and within populations. Growth in weight was more variable and appeared to be related to richness of the habitat.

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1987.tb00125.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract.Carp feeding trials were conducted to assess dietary effectiveness in relation to growth rate, cost, conversion ratio, logistics and the contribution of natural pond foods. Overall, trout pellets containing 40% protein were found to be the most effective. In laboratory trials this diet fed at 5% bwd−1produced a food conversion ratio (FCR) of 1·99. Another trout food containing 47% protein, fed at the same ration, had a superior FCR and specific growth rate (SGR) but proved more costly because of a poorer protein efficiency ratio (PER). Optimum ration size declined with increasing body size. The mammalian herbivore diets, with higher carbohydrate but low lipid levels, were cheaper to purchase but had poorer SGRs and FCRs. Some evidence of protein sparing occurred with low levels of activated sludge substitution but condition and growth rate declined above the 20% substitution level probably due to increasing heavy metal concentrations. In the pond trials extensive production levels of 300–350 kg ha−1year−1arose from zooplankton consumption. The associated SGR was around 1·70 and the FCR was calculated at 1·64 (dw) assuming 47% utilization of the zooplankton. Higher levels of production (1400–2200 kg ha−1year−1) occurred with supplementary feeding with SGRs at 1·78–2·35. The contribution of natural food was slight in intensive rearing. An FCR of 2·01 was found with trout pellets and an esti

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1987.tb00126.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract.The size selectivity of gillnets to pikeperch,Stizosiedion lucioperca(L.), and perch,Perca fluviatilis L., caught mainly wedged, was estimated by the selective use of the deterministic model of Holt (1963). The selectivity characteristics for pikeperch based on samples in gillnets with 48‐65‐mm bar mesh were:k= 0·903 and σ= 4·93cm (fork length). When a higher efficiency of large‐meshed nets is accounted for, the estimated selectivity curve shifts to the right. The condition of the pikeperch had a major influence on the position and shape o(the selectivity curve. The selectivity to perch was established with 25–35‐mm gillnets in a year with a poor food supply:k= 0·723 and σ= 2·59cm (fork length). Estimates based on literature data from an exploited perch population showed a much lowerk= 0σ639 (total len

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1987.tb00127.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Book reviewed in this article:The Economics of Fisheries Management. By LeeG. Anderson.The Ecology of Tropical Lakes and Rivers. By A. I. Payne.The Zoogeography of North American fishes. Edited by Charles H. Hocutt&E. O. Wiley.

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1987.tb00128.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY