摘要:

AbstractOffspring from a mass spawning of the Chilean oysterOstrea chilensis(Philippi) were reared in three locations, at two depths and three densities along the east coast of Chiloé Island, southern Chile, to test for the presence of genotype‐environment interaction for growth rate and the effect of environmental variables on shell growth. Site, density and depth effects and their interactions upon shell length variation at 26 months of age were all statistically significant (P<0.05). These results indicate that sibling oysters perform differently in different environments, densities and depths. The shell length ofO. chilensisin the three different environments may be limited by food supply when the abiotic variables are in the range of tolerance for the species. Salinity was the most important factor limiting the shell growth ofO. chilensisin the Quempillén estuary. Thus, in breeding programmes, it is recommended that the testing of stocks and their offsprings’performance should be carried out on the farm to ensure that the selection criteria are

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1996.tb00961.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe European flat oyster,Ostrea edulisL., has been successfully cultured in Cork Harbour on the south coast of Ireland, using non‐tidal, man‐made ponds for over 20 years. Broodstock placed in ponds spawn and the released larvae grow and settle on mussel shell cultch. This study investigates the nutrient dynamics and plankton cycles that occur from the time the ponds are filled. The incoming water to the ponds, when filled in May‐June, is usually nutrient rich, with high numbers of diatoms. The nutrients become depleted quickly and the phytoplankton becomes dominated by smaller algal species, particularly flagellates and by dinoflagellates. Following mussel shell addition, orthophosphate levels increase and this pulse in nutrients is generally followed by an increase in microplankton, particularlyChlorellaspecies. This increase often reaches bloom proportions and, if so, ponds are flushed. This addition of water increases the nutrient level and changes the phytoplankton composition, usually by introducing new dinoflagellate and diatom sp

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1996.tb00962.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractWater quality in sea‐cages, and metazoan ectoparasites on bass,Dicentrarchus labrax(L.), and bream,Sparus aurataL., were sampled at two fish farms in south‐west Greece over 2 years. The seabed and marine life around the cages of one farm was surveyed using scuba. The most frequent and abundant parasites were the monogeansSparicotyle chrysophriiandFurnestinia echeneison the gills of bream, andDiplectanum aequanson the gills of bass. The copepodCaligus minimusoccasionally occurred in the buccal cavity of bass, but only in low numbers. Prevalence and abundance of parasites increased with bass size butF echeneislevels decreased with bream size. There were no other clear relationships between water quality, parasite levels and fish size. Ammonia varied seasonally with sea temperature, and with oxygen levels below 6 mg 1‐1on many occasions, it is possible that fish suffered stress from a combination of high ammonia and low oxygen conditions. There was no accumulation of waste food or faeces below the cages at the one farm surveyed, but there were thousands of wild fish, including mullet (Mugilidae),Spicarasp. andDiplodusspp., present around the cages. Water quality may be improved by changes in farm management, such as reducing stocking densities below the present 16 kg nr‐3. Oxygen should be monitored at the cages on site daily. How comparable environmental conditions and impacts, and parasitization are at other bass and bream sea cage farms is

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1996.tb00963.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractProgeny from a cross of two strains of rainbow trout,Oncorhynchus mykiss(Walbaum), displayed about 7% heterosis in their growth rate. Variance component analysis showed that dams accounted for 20.3% to 65.8% variability in growth while sires accounted for none. Maternal effects were significant, but showed a diminishing trend over the study period. Additive genetic effects were nonsignificant. The Mount Lassen strain was better in maternal ability which indicated that source of dam was important. Interactions between sires and dams were significant with source of dam being important.Heritability for weight based on half‐sib sire component of variance was estimated at 0.020 ± 0.001 and 0.269 ± 0.016 based on the dam component. Heritability for growth rate was 0.27 ± 0.04 based on the sire component and 0.88 ± 0.35 based on the dam component.Fulton's condition factor was lower in the hybrids. Egg size was correlated with fish size in the early growth phase. It was concluded that crossbreeding of rainbow trout strains could be advantageous owing to the display of hybrid vigour in the pr

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1996.tb00964.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe various components of the nitrogen budget of white steenbras,Lithognathus lithognathusCuvier (Sparidae), were determined under experimental culture conditions. A simple closed system respirometer was used where experiments were conducted to investigate faecal prodution, nitrogen excretion rates and absorption efficiencies at 16C and 20C. Faecal loss, as a percentage of the ingested nitrogen, amounted to 3.59%. Gross, carbon and nitrogen absorption efficiencies ranged from 8 6 to 9 8 % and were not significantly affected by fish size, ration size or temperature (P<0.05). Net protein utilization (NPU) and the biological value (BV) ranged from 78 to95%. Ammonia and urea constituted 77.93 and 10.07%, respectively, of the total exogenous nitrogen excretion, the balance being made up of other dissolved organic nitrogen (DON). Endogenous ammonia excretion rates were significantly greater in small fish compared to large fish (P<0.05). Total non‐faecal losses as a percentage of the ingested ration amounted to 21.86%. Fish size and ration size increased nitrogen excretion, but temperature had no effect. Maintenance rations were 7.55 mg g‐1dry weight day‐1(0.76%dry body weight) and 5.99 mgg‐1(0.60% dry body weight) for small and large fish, respectively. The high absorption efficiencies and high nitrogen indicated that white steenbras utilize the commercial trout pellet diet very effi

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1996.tb00965.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractAnnual cycles of gamete development inMytilus edulisL. in south‐west Iceland were investigated during 1986 to 1987. Histological preparations of the gonads showed that all individuals were fully mature in the beginning of June in both years and one spawning period was recorded each year at a sea temperature of 10‐12oC. The main spawning took place from the middle of July to the middle of August, and from the middle of June to the end of July in 1986 and 1987, respectively. Redevelopment of the gonads after spawning was observed in February when both food availability, measured as chlorophyllaconcentration, and temperature were low. Rapid gonad maturation took place during the spring phytoplankton bloom in March‐April.Larval settlement was heavy on the artificial collectors used. The length of the larval period was estimated as being 4‐5 weeks and peak settlement occurred in the middle of September. The size of the early plantigrades settling on the collectors during the study period indicated direct settlement of mussel larvae from the plankton onto the collectors.One year after settlement the spat averaged 24.6 mm ± 6.0 (SD) shell length and two years after settlement a market size of 50.8 mm ± 5.7 (SD) was reached. Growth was correlated with food availability, measured as chlorophyllaconcentration. The growth season lasted from March to October with the greatest shell growth in late summer. The results showed that the growth of M.eduliswas markedly increased by suspending the animals in a more favourable environment than that found on the natural mu

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1996.tb00966.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractAnimal by‐product meals (ABM) were substituted for fish meal in five experimental diets for Nile tilapia fry,Oreochromis niloticus(L), with 25%, 50%, 75% and 100% substitution. Two diets with 100% ABM were tested, one with 50:50 animal lipid:soybean oil, and the other with 100% fish oil as attractant. In general, the best growth and feeding performance was obtained with a control diet based on fish meal as the sole protein, but the results were not statistically different from those obtained with 75% and 100% ABM with soybean oil. A simple cost analysis suggested better economic efficiency when tilapia were fed with 100% ABM. It was concluded that animal by‐product meal can be used as a sole protein source in commercial diets for Nile tilapia fry, without affecting growth and food utilization of the fish, improving the economics of feeding in comparison with fish m

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1996.tb00967.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Books Review in this article:Aquaculture. Biology and Ecology of Cultured Species. Edited by G. Barnabe. Ellis Horwood, Chichester UK.Embryology in Fish: A Review. By J. Depeche&R. Billard. Société Française ď Ichtyologie, Paris.Flowing Water Fish Culture. By Richard W. Soderberg. CRC Press, Boca Raton, Fl.Aquaculture Water Reuse Systems: Engineering Design and Management. Developments in Aquaculture and Fisheries Science Volume 27.Edited by M. B. Timmons&T. M. Losardo. Elsevier, Amsterdam. 1

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1996.tb00968.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1996.tb00969.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY