摘要:

AbstractA simple method is presented for determining the optimum time to harvest fish and the effect of fertilization type on optimum harvest time for Aquaculture. Optimum harvest time was similar for either maximizing fish yield or maximizing profit of fish harvested (price of fish times fish yield minus fish production cost), because the daily change in fish production cost was low for the low‐input Nile tilapia,Oreochromis niloticus(L.), production system in Thailand. At a harvest time of 150 days for an organic fertilization treatment compared to an inorganic fertilization treatment fish yield increased from l‐505 t/ha to 2‐295 t/ha, and profit of fish harvested increased from 15657·1 baht/ha (US$ 590‐8/ha) to 25127·5 baht/ha (US$ 948‐2/ha). For the organic treatment, optimum harvest time occurred at 191 days, with a fish yield of 2·328 t/ha and a profit of 25520·5baht/ha (US$ 963·0/ha), compared to the inorganic treatment where optimum harvest time occurred at 105 days with a fish yield of 1·536 t/ha and a profit of 16035·4baht/h

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00807.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractCircular tanks are appropriate forClarias gariepinus(Burchell) culture. Wide/shallow tanks (with a diameter to depth ration of about 10) are preferable to narrow/deeper tanks. The optimal flow rate for larvae will be one which provides sufficient oxygen yet does not generate a current velocity fast enough to cause them to swim against it. However, current velocity, for a given type and orientation of inflow, will depend particularly upon tank diameter to depth ratio and flow rate and will be related to position within the tank. Therefore for a given circular tank design a theoretical maximum flow rate and concomitant biomass can be estimated for a given mean fish size. Once airbreathing begins the optimal flow rate for fry is simply that which does not elicit swimming.

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00808.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractIn a cod enhancement project in a small fjord in western Norway, two groups of reared cod,Gadus morhuaL., were released with 6 months’difference in time. After the last release a 3‐week fishing survey was conducted. Stomachs from wild and recaptured reared cod of similar size were sampled and analysed. The last released cod had learned to catch the same prey types and in the same relative proportions as the wild cod the second week after release, but mean weight of stomach contents and mean numbers of prey items per stomach were smaller, and a larger proportion of the newly released fish had empty stomachs. Three weeks after release the proportion of empty stomachs was similar to that of wild cod and the first released reared cod, but the food intake was still smaller. The first released group of reared cod, which had spent 6 months in the fjord, seemed to feed as efficiently on wild prey as did wild

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00809.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractFailure to achieve feminization of tilapia under conditions where masculinization is successful was attributed to earlier determination of testis development than of ovary development. Success in obtaining sex inversion by immersion of eggs and fry of salmonids in hormone solutions suggested the possibility of obtaining sex inversion by treatments applied at early life stages. Thence, tilapia embryos were exposed to oestrogens as early as possible after fertilization, by incubating the eggs in oestrogen solutions. Further treatments consisted of rearing the fry in oestrogen solutions for various durations. Eggs ofOreochromis mossambicus(L.) and ofO. mossambicus×O. urolepis hornorumTrewavas were collected from the mouths of females immediately after spawning and incubated in Erlenmeyer flasks set in a water bath shaker, at 27°C. The following oestrogenic hormones (dissolved in ethanol) were added to the flasks: 17β‐oestradiol, progesterone, flutamide, and flutamide + progesterone. Initial treatments were given at concentrations of 1‐50αg/l, for different durations ranging from 7 to 30 days after spawning. Due to high mortalities, higher doses (i.e. 100‐5000αg/1) were tested for shorter periods (from 2 hours to 12 days). No sex inversion to female or to intersex gonads was achieved in any of the immersion

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00810.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractCarp respond to water hypoxia with an evaluation in the rate of gill ventilation. In order to characterize closer the adequate stimulus for the increase in respiratory drive specimens of carp,Cyprinus carpioL., were exposed simultaneously to moderate environmental hypoxia (PwO2˜ 75mmHg, 10kPa) and elevated water nitrite concentration (089 ± 0‐lmmol/l) for 24h. The differential effects of these treatments were utilized to distinguish between the responses to an immediate reduction in water and arterial Poa(P,O2), and to the slowly developing reduction of arterial oxygen content (CaO2) and functional oxygen saturation (SaO2). After onset of hypoxia gill ventilation quickly increased, leading to a reduction in PaCO2. Slowly rising blood methaemoglobin levels resulted in a gradual decline in CaO2and SaO2over 24h, whereas P002 remained steady for the entire exposure period. This pattern of lowered Paco2and PaO2, essentially constant for 24 h, together with the lack of any correlation with changes in CaO2, suggests PO2(Pa,O2and/or Pwo2) as the primary stimulus in the regulation of ventilation of c

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00811.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractTo monitor the success of stockings of hatchery‐reared barramundi,Lates calcarifer(Bloch), in tropical Australian waters a series of laboratory and field experiments were undertaken to evaluate a range of marking techniques. Juvenile fish of stocking size 30‐85 mm total length were first used in laboratory experiments and then some were stocked into a freshwater impoundment for field evaluation. Marking techniques evaluated were fin crimping, fin removal, cold branding, polyethylene streamer (ags and coded‐wire tags. The results showed that dorsal fin crimping and pelvic fin removal were relatively ineffective methods of marking, with only 53% and 63% of marks in each respective group being recognizable after 3 months. The polyethylene streamer tags were quickly shed, with 100% loss after only 77 days. Cold brands faded rapidly and were not considered to be of value as long‐term marks. Coded‐wire tags, inserted into the cheek musculature, were considered to be the most successful of the techniques assessed. Coded‐wire tags were implanted at a rate of 250‐270 tags per hour with an immediate success rate of 95‐97%. These tags had no significant detrimental effect on either growth or survival and tag retention in the 2‐month laboratory trials was 93%. Longer‐term field studies, where fish had been stocked for about a year, also suggested little effect of coded‐wire tags on growth or survival and no

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00812.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractA descriptive account of the fisheries in the lower Sondu‐Miriu River of the Lake Victoria catchment before the construction of a hydroelectric dam is presented. It can support an annual yield of 81‐5‐1081 and a catch rate of 11.4kg/ha/h. Out of the 28 species present in the river, the most abundant wereClarias gariepinus(Butchell),Schilbe mystus(L.),Synodontis afrofischeri(Hilgend),Oreochromis variabilis(Boulenger),O. leucostictus(Trewavas), andLates niloticus(L.),Micropterus salmoides(Lacepède) andL. niloticusare a new development in the river fishery introduced respectively from the highland areas and Lake Victoria. The yield in the river has been reduced from 668t in 1959 to the current 108t and species available replaced the once abundantBarbus altianalis(Boulenger) andLabeo victorianus(Boulenger). This drastic reduction in yield can be attributed to overfishing, habitat degradation and poor management. The upstream migration of the river fishes extends as far as 10km from the Lake Victoria river‐mouth. The period of peak reproductive activity (March‐June and October‐November) coincides with the established rainy seasons in the region. The top ranking food items of the fishes are terrestrial and aquatic insects, vegetable matter, detritus, crustaceans, molluscs, fish, plankton and grit. The endemic fish stock appears to be in a depressed state, showing signs of overexploitation, and therefore careful stocking programmes to restore the fish balance would be appropriate. Fishing effort in the river should be regulated by licensing of nets and the minimum size of fish landed should be regulated through cooperative societies, clans, party elders and other social o

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00813.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractEscaped reared salmon, Salmo salar L., were distinguished from wild salmon in the catch of a coastal salmon fishery on the west coast of Scotland. The stomach contents of 54 escaped fish were examined to determine their recent feeding history and 19 (35%) were found to contain food. The predominant prey were juvenile whiting,Merlangius merlangus(L.), unidentified Gadidae and sandeels (Ammodytidae), although other fish and invertebrates, mainly post‐larval hermit crabs (Paguridae), were recorded. All these prey are pelagic or semi‐pelagic. These observations demonstrate that escaped salmon feed on natural prey in coastal waters and extend our knowledge of the diet of salmon in their marine ph

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00814.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Book Review in This Article:Introduction to Aquaculture. By MATTHEW LANDAU.Population Genetics: Diversity and Stability. By YURI P. ALTUKHOV. Translated from Russian by J. H. Appleby. Edited by John Beardmore.Inland Fishes of India and Adjacent Countries. P.K. TALWAR A. G. JHINGRAN.A Natural History of the Lakes, Tarns and Streams of the English Lake District. Geoffrey Fryer&Sharon Murphy.

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1992.tb00815.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY