摘要:

Abstract.An intensive growth trial conducted In pens in an earthen pond indicated that growth ofPenaeus vannamei(Boone) increased with feeding frequency and suggested that day feedings produce greater growth than night feedings. The differences in growth due to feeding frequency were significant, instantaneous growth rates (IGR) increasing from 1·62% to 1·66% to 1·71%/day as the number of feedings increased from one to two to four per 24 h. Comparison of the IGR of shrimp fed at night (1·64%/day) to that of shrimp fed during the day (1·68%/day) suggested (P= 0·0633) that growth was greater for shrimp given day feedings than for shrimp given night feedings. Survival of shrimp was not significantly different due to feeding frequency or due to time of feeding and averaged 74·7 ± 6·1%. Results indicate thatP. vannameicultured under conditions similar to those tested should be fed a minimum of four times daily and suggest that feeding during the day is at least as good as and may be preferable to feeding

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00823.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.The endangered Australian freshwater fish trout cod,Maccullochella macquariensis(Cuvier), was the subject of a captive breeding programme to produce fry for reintroduction into the wild. Trout cod broodfish were maintained in earthen ponds for up to 5 years and underwent gonadal maturation each spring but did not spawn in the ponds. Infestations of the protozoan parasiteChilodonella hexastichacaused the death of at least 21 broodfish. Mature fish, removed from ponds when water temperatures had reached or exceeded 16°C, had a higher proportion of atretic oocytes and fewer fish spawned successfully compared to fish removed at lower temperatures. Ovulation was induced by a single injection of 1000–3000 iu/kg HCG. Between 1188 and 11338 eggs ranging from 2·5 to 3·6 mm in diameter were stripped from individual fish. Hatching commenced on days 5–9 and continued for up to 10 days (at 15·5–23°C). Larvae commenced feeding on days 21–25. Trout cod larvae were grown out to fry (363.3–48.6mm total length [TL]) in fertilized fry rearing ponds then released. Between 1986 and 1989, 8420 trout cod fry were released into several sites in the upper Murray River and upper Murrumbidgee River, and reports indicate that released fish

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00824.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.Directly counted bacteria increased in abundance in water passing through a trout farm in north‐east England and were not removed by a settling lagoon. Total bacteria in the effluent were such that they might potentially bring about immediate increase in the bacterioplankton populations of recipient rivers. Directly counted bacteria increased cumulatively through rows of well‐stocked fish ponds arranged in series, thus all ponds contributed to the increase in suspended bacteria. In contrast, bacterial numbers varied irregularly through rows of low‐density stocked and fallow ponds. The increase in bacteria in well‐stocked ponds was greatest shortly after the daily feedi

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00825.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.The aims of the present study were to determine the number and age structure of grey herons,Ardea cinereaL., visiting a large freshwater cage trout farm in a study area in Argyll, western Scotland and to quantify heron predation at the site. Heron abundance was assessed on sea loch shores, running and standing freshwater bodies and at the trout farm between September 1985 and August 1987. Herons visited the farm almost exclusively at night or during twilight periods and, as a consequence, were seen more often by farm staff in winter than in summer. Herons selected cages containing small trout (<300g) and removed them from cages by standing on the top nets and fishing through the mesh. Stock losses were of two kinds; trout were either eaten directly or were dropped by herons during manipulation, when characteristic wounds increased susceptibility to disease or made the fish unmarketable. Adult herons were more successful at feeding than first‐years and although younger birds spent more time feeding their intake rates remained lower than those of adults in terms of their total time at the farm. Within a cage, smaller fish aggregated closer to the surface than larger ones and so were more vulnerable to heron predation. In many cases, a high proportion of the fish attacked by herons were blind and/or in poor condition. By recording only wounded fish, farm staff considerably underestimated their losses to herons. Nevertheless, attacks sometimes appeared serious to farmers. However, such losses were small compared with other forms of fish mortality and los

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00826.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.The effects ofArtemiaspp. and of Moina micrura from two culture sources, poultry manure andChlorellasupplemented with baker's yeast, on production ofMacrobrachium rosenbergii(de Man) post‐larvae (PL) were evaluated. Significantly higher production of 18·13 ± 1·45 PL/I was obtained for the larvae fed with 50:50 mixture ofArtemiaandMoinacultured on poultry manure compared to that for larvae fedArtemiaalone (14·27 ± 1·64PL/I). Regardless of the culture source, the post‐larval production was the lowest (9·23 ± 1·22 and 11·26 ± 1·33 PL/I for the larvae fedMoina.The higher dietary value ofMoinacultured on poultry manure was related to the high content of n–3 HUFA particularly 20:5n‐3 compared toArtemiaandMoinacultured o

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00827.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.Growth and survival response ofPenaeus stylirostris(Stimpson) to fertilization, pelleted feeding and stocking density were analysed for the conditions prevailing on the Baja California peninsula (Mexico). Three 0·25‐ha earthen ponds were longitudinally divided in half with mesh structures. One half received inorganic fertilization (trial F) and the other supplementary feeding using a pelletized ration (trial PF). The initial stocking rates were approximately 5, 10 and 15 PL5/m2in both trials. After 210 days, final mean weights ranged from 15·0 to 5·3g and survival from 48·6 to 17·8%. Growth and survival were analysed by means of a reparameterization of the von Bertalanffy's growth model and the exponential mortality equation. Results indicated that: (1) final mean weight was dependent on density in both trials (P<0·01) although growth rate was only affected in trial PF (P<0·01); (2) pelleted feeding produced both greater final mean weight and increased growth rate at densities higher than 5 PL/m2(P<0·005); (3) the ratio tail weight/total weight was influenced by density in trial F (P<0·015); (4) the mortality equation served to explain differences in survival to a limited extent. An increase in growth rate after 170 days occurring at the intermediate density in trial PF was attributed to an increase in mortality, which allowed the remaining individuals to attain larger sizes. Further research to increase biomass yields should focus on the optimization of pond depth, the supply of vigorous post‐larvae and on the possible influences of seasonal variations of planktonic communities of the lagoons on the productiv

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00828.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.The effect of stocking density on growth and survival ofOreochromis niloticus(L.) fry was evaluated.O. niloticusfry (average weight, 10·56 ± 0·28mg and average length. 9·09 ± 0·05nim) were stocked in 2–1 tanks at 2, 5, 10, 15 and 20 fry/1 and reared for 33 days post fertilization, at 30°C (±1°C). Mean lengths, mean weights, and specific growth rates were found to be significantly lower (P<0·05) at the higher stocking densities. The coefficient of variation for the five stocking densities was significantly (P<0·05) different. Condition factors, however, were not significantly (P<0·05) different and survival was high at all density treatments. These data suggest that the culture ofO. niloticusis feasible at the density groups tested but 5–10fry/I is recommended for fry culture in the hatchery, if a more uniform

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00829.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractGrowth performance, feed utilization and changes in body composition ofColossoma macropomum(Cuvier) juveniles — in the weight range 2 to 200g — fed an artificial high protein diet, have been analysed against feed ration and fish weight. A polynomic equation is developed which permits prediction of growth and radon parameters in this weight range. The results are compared with the values of other cultured common freshwater fish species.Colossoma macropomummust be considered a very fast grower with good feed utilizat

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00830.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.The growth and survival of groups of juvenile sole,Solea solea(L.), fed exclusively fresh or heat‐treated and frozen (stored) mussel,Mytilus edulisL., were compared and the effect of supplementing the stored mussel with one and two feeds per week of fresh mussel was assessed. Over the 9 weeks of the experiment the survival of the fish fed fresh mussel exceeded 90%. In contrast, less than 3% of those fed stored mussel alone survived. The inclusion of two feeds per week of fresh mussel increased survival to the same level as that of the groups fed only fresh mussel, though growth rates were significantly lower. The mortalities of the fish fed stored mussel were associated with an outbreak of the disease ‘black patch necrosis’ (BPN). The fish fed fresh mussel did not develop the symptoms of this disease despite their proximity to diseased fish and the lack of precautions to prevent its spread. The fish were not provided with a sand substrate, often considered necessary for sole ongrowing. It is suggested that a combination of adequate nutrition and attention to tank cleanliness is sufficient to avoid the occurrence of BPN and that the provision of a sand substrate is not a prerequisite for successful culture of juvenile

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00831.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.In a parasitic survey of wild and cultured sea bass,Dicentrarchus labrax(L.), thirteen protozoan species were found. Ectoparasites included two ciliates (Trichodinaspp.), one dinoflagellate (Amylodiniumsp.) and one zooflagellate (Cryptobiasp.). Endoparasites were represented by members of Apicomplexa (Hemogregarinasp.,Eimeriaspp.). Microsporea (unidentified species) and Myxosporea (Myxobilatussp.,Ceratomyxaspp.,Sphaerospora dicentrarchi, Sphaerospora testicularis). Myxobilatussp.,Eimeriaspp. and the microsporean were exclusively found in wild fish, whereasAmyloodiniumsp. andHemogregarinasp. were only detected in cultured fish. Data on prevalence and intensity of infections and on the location in the host are provided. The potential importance of protozoan parasites for sea bass culture is discussed.

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1993.tb00832.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY