摘要:

AbstractA 3 × 3 factorial experiment was conducted with Mozambique tilapia.Oreochromis mossambicus(Peters), using satiate feeding with 25%, 30% or 35% dietary protein concentrations each with three energy concentrations 10.5,12.6 or 14.7 kJ per g of purified diets. Protein‐to‐energy ratios (P/DE ratio) ranged from 17 to 33.4 mg protein kJ−1of digestible energy (DE). Diets were fed to triplicate random groups of 15 fingerlings for 62 days in glass aquaria.Improvement in both weight gain and feed conversion rate (FCR) was achieved when dietary protein increased (P<0.05), while increasing dietary energy concentration reduced feed consumption and increased mortality (P<0.05). Protein efficiency ratio (PER) increased as dietary protein decreased and as dietary energy increased (P<0.05).P/DE ratio correlated positively with gain, energy retention (ER) and feed consumption (r= 0.96,0.96 and 0.73 respectively) and negatively with feed conversion rate (FCR), protein productive value (PPV), protein efficiency ratio (PER) and mortality (r= ‐0.93, ‐0.95. ‐0.91 and ‐0.84 respectively). Weight gain had a positive relation with feed consumption (r= 0.82).The optimum P/DE ratio in purified diets for Mozambique tilapia for rapid growth, efficient feed conversion and maximum retention of protein and energy appears to be approximately 23.8 mg of pro

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1995.tb00935.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThis paper provides baseline information on the involvement of women in small‐scale coastal aquaculture such as the farming of slipper oyster,Crassostrea iredalei(Faustino 1933), and green mussel,Perna viridis(Linnaeus 1758). Data were gathered during a socio‐economic survey of oyster and mussel farming in Western Visayas, Philippines conducted from July to December 1991.There were 175 respondents interviewed; 18.5% and 2.4% of oyster and mussel farmers were females. Fishing and related activities were the major source of livelihood for the majority of oyster and mussel farmers. In 1990, 79.4% and 69.8% of oyster and mussel farmers earned an annual income of less than P30 000 (1 USS P23). Based on the 1988 (latest data available) poverty threshold of P2654 (monthly) for Western Visayas, 80.4% and 71.7% of oyster and mussel farmers lived below poverty level in 1990. of 175 respondents. 79.3% and 48.2% of oyster and mussel farmers indicated that their household members participated in farming activities. More female household members were involved in oyster farming compared with mussel farming. Harvesting in mussel farming and both harvesting and marketing in oyster farming generated the widest participation among female household memb

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1995.tb00936.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractCage farming of salmonids in floating cage systems has become widespread in the Scottish Highlands over the past 15 years. Determination of wastewater discharges and composition from such facilities, unlike land‐based ones, has had to rely exclusively upon results of published studies of waste outputs. To limit impacts of such activities, regulatory authorities have used such data together with lake nutrient mass‐balance models to assess likely increase in phosphorus (P) due to both organic and inorganic loading of cage farm losses. Results of biannual surveys between 1988 and 1991 of P levels in six lochs used for cage farming in Scotland, together with estimates of nutrient input on the basis of feeding and fish biomass data, are presented. Results demonstrate that in small basins, where cage farms are the only substantial source of P. model predictions of rises in P level reflect actual changes in water quality. However, in larger, more complex basins, where cage farms represent one of a number of sources of P, and the mass of P present in the nutrient cycle is far greater, use of such models is found to be inappropriate to assess the impact of such operations. Clear effects on loch nutrient levels are observed in the immediate vicinity of the cages. It is concluded that whilst such mass‐balance models may estimate total contributions from cage farms accurately, use of such models to determine annual nutrient dynamics of complex sites requires more robust sampling programmes than have at present been implem

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1995.tb00937.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractA study was conducted onOreochromis spilurus(Günther) fry (9.0 mm) in sea water (38‐40%o) to evaluate the effects of three doses (40, 70 and 100 ppm) of a synthetic oestrogen, 17α‐ethynyloestradiol (17‐EE) on the feminization, specific growth rate (SGR), food conversion efficiency (FCE), condition factor (CF) and survival rate. The fry were fed a hormone‐impregnated diet for 42 days, followed by a hormone‐free diet for another 77 days. At the end of the experiment (119 days), successful feminization was obtained in all groups treated with 17‐EE. The dose of 100 ppm was the most potent one and induced 92.2% sex reversal. At the end of the hormone‐treatment phase (42 days), all groups treated with 17‐EE and the untreated controls showed no significant differences in growth, SGR, FCE, CF, and survival rate. After 119 days, a significant difference was detected only in the mean body weight and total length where the EE‐100 group had the highest values. However, this was due to the low survival rate in this group (37.5%) and not to any possible anabolic effect of 17‐EE. The findings of this study indicate that seawater sex reversal ofO. spilurusis possible and 100% sex reversal could be achieved by slightly increasing the dose and/or dura

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1995.tb00938.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe expansion of freshwater cage culture in Scotland during the 1980s led to concern with respect to the impact of nutrient, particularly phosphorus (P), discharges on water quality in lakes. The primary route by which P enters the aquatic environment from cage farms is through the feed administered to the fish. In recent years, there have been considerable technological advances in feed manufacturing and improved feeding practices at farm level. This paper investigates how P inputs to freshwater lakes from cage farms may be reduced through changes in diets and improved food conversion ratios. The results demonstrate that there has been a significant improvement in the P content of freshwater trout diets in recent years and that it is possible to reduce waste P loadings from cage sites through the use of better‐quality diets and improved feed management. In Scotland, production levels in freshwater cages are commonly set by the regulatory authority assuming a soluble waste P loading of 10 kg P tonne−1of fish produced. This study suggests that actual soluble waste P loadings are likely to be far lower than this and that, as a result, increases in water column total P levels may be overestima

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1995.tb00939.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractSpatfall of pearl oyster,Pteria sterna(Gould), was analysed at two sites, stations Gaviota and Merito, at Bahía de La Paz, South Baja California, Mexico, during an annual cycle in 1991‐1992. and from surface to 15 m depth. Sampling was carried out monthly using experimental collectors which remained immersed for 60‐65 days. Four different substrates were tested for spat settlement preference: a native bush called ‘chivato’, dry palm leaves, and red and yellow plastic onion bags: temporal variations, and horizontal and vertical spatfall distribution patterns were evaluated between and within stations.Spat settlement showed significant differences depending on the structure and texture of the substrate type. Chivato bush was in general the best spat collector, but was difficult to handle for large‐scale operations; plastic onion bags were more suitable and spat yield was adequate; palm leaves were poor spat collectors. There was no evidence for colour preference of spat settlement between red and yellow onion bags.Pteria sternaspat were present throughout almost all of the study period. Main spatfall was detected in winter‐spring, coinciding with low temperatures; most spat then occurred from surface to 4‐5 m depth. Few spat were present in summer and most then occurred below 7‐9 m depth. The distribution patterns of spat within substrate replicates were apparently influenced by the abundance of spatfall. Aggregated spatial patterns were evident in shallow water during months of maximum spatfall but not when spat was less abundant. These events did not occur in the same substrate type, and differences were also detected between stations. Trends were related to oceanographic conditions prevailing at each site.Two patterns of spatfall abundance and vertical distribution were evident, one for winter‐spring, and the other for summer. Samples at station Gaviota were grouped by spatfall abundance and spat vertical distribution patterns, while the latter defined better the grouping of samples at station Merito.Geographical variations of spatfall characteristics for Pteriasternaitself, and in comparison withPinctada mazatlanka(Hanley) in the Gulf of Califor

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1995.tb00940.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY