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1.
This study presents results from an experimental 10-day research charter that was designed to quantify the effects of (a) a turtle excluder device (TED), (b) a radial escape section bycatch reduction device (BRD) and (c) both devices together, on bycatch and prawn catch rates in the Queensland shallow water eastern king prawn (Penaeus plebejus) trawl fishery. The bycatch was comprised of 250 taxa, mainly gurnards, whiting, lizard fish, flathead, dragonets, portunid crabs, turretfish and flounders. The observed mean catch rates of bycatch and marketable eastern king prawns from the standard trawl net (i.e., net with no TED or BRD) used during the charter were 11.06 kg/hectare (ha−1) (S.E. 0.90) swept by the trawl gear and 0.94 kg ha−1, respectively. For the range of depths sampled (20.1–90.7 m), bycatch rates declined significantly at a rate of 0.14 kg ha−1 for every 1 m increase in depth, while prawn catch rates were unaffected. When both the TED and radial escape section BRD were used together, the bycatch rate declined by 24% compared to a standard net, but at a 20% reduction in marketable prawn catch rate. The largest reductions were achieved for stout whiting Sillago robusta (57% reduction) and yellowtail scad Trachurus novaezelandiae (32% reduction). Multidimensional scaling and analysis of similarities revealed that bycatch assemblages differed significantly between depths and latitude, but not between the different combinations of bycatch reduction devices. Despite the lowered prawn catch rates, the reduced bycatch rates are promising, particularly for S. robusta, which is targeted in another fishery. Prawn trawl operators are not permitted to retain S. robusta and the devices examined herein offer the potential to significantly reduce the incidental fishing mortality that this species experiences.  相似文献   

2.
Ecuadorian Penaeus vannamei were cultured in dirt ponds (each of approximately 163 m2) at four different stocking densities, i.e. 5 shrimp m−2, 10 shrimp m−2, 15 shrimp m−2 and 20 shrimp m−2. Experiments were carried out over three different periods during the year. Each experiment lasted for 11–14 weeks. No commercial feed was given to the shrimp. The only input to the ponds was about 30 kg of cattle manure per pond per week. Chemical composition of the cattle manure was analyzed. Water quality parameters such as temperature, pH, DO and turbidity were recorded twice daily for each experiment; nutrients (nitrite, nitrate, ammonium and phosphate), water ATP, sediment ATP, H2S and chlorophyll were measured twice weekly for each experiment. Shrimp were sampled either weekly or bi-weekly for body weight measurements.

The results showed a negative correlation between stocking density and growth. Weekly growth ranged from 0·44 to 1·58 g week−1. Survival was over 50% in all treatments and averaged at 70·8%. Under these stocking densities, shrimp production ranged from 4·4 to 18·8 kg ha−1 day−1. The stocking density of 15 shrimps m−2 provides better production than the other stocking densities.

Water quality data did not relate to any shrimp growth. Water nutrient levels in pond discharge water were less than or equal to the nutrients in the incoming water in spite of the weekly addition of cattle manure and did not increase with the addition of cattle manure. No coliform bacteria were detected in any pond water samples through the study period. This indicates digestion of cattle manure in marine shrimp ponds would not pollute the environment with high concentrations of dissolved nutrients.

Thus, a marine shrimp pond can be considered a dissolved nutrient marine treatment plant converting unwanted cattle manure (1841 kg cattle manure ha−1 week−1 in this study) into a valuable commodity — shrimp.  相似文献   


3.
A simple tank system, using artificial aeration to supply oxygen and incoming water to dilute metabolic by-products and other wastes, was tested. Blue tilapia, Oreochromis aureus, were grown under a wide range of loads, 7–31 kg liter−1 min−1, and densities, 19–77 kg fish m−3 culture unit. Average yield ranged from 6–10 kg m−3 culture unit per month. Approximately 14–20 m3 of water was used for each kilogram of fish produced.  相似文献   

4.
The current ‘traditional’ prawn pond management system really does not ‘manage’, but rather accommodates prawn production characteristics and was instituted with a minimum knowledge of prawn biology and husbandry. As such, the traditional system is not optimal because it does not rely on a strong empirical knowledge base. Prawn culture has succeeded up until now because Macrobrachium rosenbergii is easily cultured and will give 500–1000 kg ha−1 year−1 without much effort. This is sufficient in many areas of the world but not in others where economic conditions have break-even production requirements of nearly 1 tonne greater than this. The traditional system relying on selective harvesting with large seine nets is seriously inefficient which not only leads to lost revenue but under-manages pond growth since unculled large animals suppress the growth of unculled smaller ones. The degree to which this occurs was not known to the designers of the traditional system who had no way of knowing (as we do now from our research results) the extremely large compensatory growth capability of small prawns in the absence of large ones. The traditional system also does not manage sexual dimorphic growth because no technology exists which can be used to create monosex broods or manipulate the sex ratio in ponds. Accurate production models are not available because traditional ponds are rarely sampled and/or rarely drained. This, along with inefficient harvests, results in a co-mingling of cohort stocking classes. It is impossible to get accurate survival and growth data because of this and because it is so time consuming to sample commercial ponds and process the data on a regular basis. This paper describes four new engineering and ‘bioengineering’ techniques which are under development and can overcome all the drawbacks of the traditional system: (1) surgical sex reversal to create monosex broods; (2) genetic tagging of stocking and resident cohorts to assess survival and growth; (3) size grading and 100% efficient harvesting using pond draining and a machine grader-harvester; and (4) a semi-automated computer assisted prawn sample data management system which uses sonic digitization of prawn sample data.  相似文献   

5.
A land-based culture facility for research on yellowfin tuna, Thunnus albacares, was developed at the Achotines Laboratory in the Republic of Panama. Six concrete tanks, and seawater and life support systems were built to maintain a yellowfin broodstock. On average, 50% of the yellowfin caught survived capture and handling, and approximately 30% became broodstock in Tank 1 (17 m diameter, 6 m depth) or Tank 2 (8.5 m diameter, 3 m depth). Each fish was tagged with a microchip implant tag, then weighed, measured, and injected with oxytetracycline (OTC) prior to stocking. Daily rations of primarily market squid, Loligo opalescens, and Pacific thread herring, Opisthonema spp., were regulated based on the feeding activity and energy requirements of the fish. Feeding activity of the broodstock decreased when the water temperatures decreased, and the fish ate decreasing daily rations and increasing calories with increasing size. Spawning occurred in both tanks within 6–8 months of capture. Spawning first occurred in Tank 1 when 24 females ranged in size from 6 to 16 kg and 65 to 93 cm fork length (FL). Spawning was intermittent during the first 2 months and occurred near daily thereafter. Tank size appeared to affect survival rates, the types of mortalities that occurred, and the growth of the fish. Survival rates after 1 year in captivity were higher, and the fish were larger, on average, in Tank 1 than in Tank 2. Most of the mortalities in Tank 1 were the result of wall strikes, which occurred more frequently after the fish reached their highest density of 0.64 kg m−3 and sizes greater than 96 cm FL and 19 kg. Non-linear growth models were fitted to the initial stocking sizes and final sizes of fish that died or were removed from Tank 1 during 1996–1999. Estimated growth rates in length (11–48 cm year−1) for fish between 51 and 150 cm FL decreased with increasing length. Estimated growth rates in weight ranged from 9 to 19 kg year−1 for fish less than 19 kg and 20–23 kg year−1 for fish greater than 19 kg. The results of this work demonstrate that the stable environment of a land-based culture facility may be the preferred system for long-term maintenance of a yellowfin broodstock.  相似文献   

6.
A stocking density experiment was conducted in 18 experimental enclosures within a single 0.11 ha pond. As stocking density increased in the range 6.1–21.2 prawns/m2, school prawn growth declined while survival rate was unaffected and total harvest (final biomass) increased. A simple economic analysis indicated that the optimum stocking density for juvenile school prawns was 19.1 prawns/m2. In a similar experiment the effects of feeding school prawns with a pelleted diet at a range of supplementary feed rates (0–12.5% of prawn biomass/day) were investigated. The optimum feed rate in terms of growth was approximately 5% of biomass/day. However the optimum feed rate, in terms of the economic return index used, varied depending on the estimated cost of the diet.  相似文献   

7.
The nutritional response of Litopenaeus schmitti larvae to substitution of Chaetoceros muelleri by Spirulina platensis meal (SPM) was evaluated. The substitution levels (S) were 0%, 25%, 50%, 75% and 100%, dry weight basis. Final larval length (FL) ranged from 1.98 to 3.16 mm for the different substitution levels. There was a significant relationship between S and FL, described by the following quadratic equation: FL = 2.853 + 0.01598S − 0.000233S2. The substitution level (S) yielding maximum FL was 34.2%. Development index (DI) values ranged from 2.84 to 3.93 and were dependent on substitution level. The corresponding equation was DI = 3.799 + 0.00945S − 0.000189S2 (P < 0.01). Maximum DI was obtained at 25.0% substitution. Survival was high (82–87%) and no significant differences were found between treatments. Protein digestibility of either microalgae was high, with 92% for SPM and 94% for C. muelleri, with no significant differences between them. The results in this study indicate that an adequate balance of nutrients in relation to the requirements of the species is critical. To simultaneously improve FL and DI, a 30% substitution of C. muelleri by SPM is suggested. This is equivalent to feeding 0.15 mg larvae− 1 day− 1 dry weight basis of a 70% C. muelleri/30% SPM diet, representing 0.078 mg protein larvae− 1 day− 1, 0.026 mg lipids larvae− 1 day− 1 and 2.732 J larvae− 1 day− 1.  相似文献   

8.
The effects of stocking density, light and shelter on the growth and survival of Clarias gariepinus fingerings was evaluated. In this experiment African catfish with initial individual mean weight 0.79±0.1 g were reared at two different stocking densities—5 fish l−1 and 10 fish l−1 in either sheltered or unsheltered tanks with reduced and normal light condition. In all conditions growth rate was significantly affected by stocking density. The growth rate was significantly higher at low densities and in reduced light conditions where shelter was provided. Survival rate was in excess of 79% in all treatments and was not affected by treatment.  相似文献   

9.
The safety and efficacy of emamectin benzoate, administered in-feed to Atlantic salmon smolts, Salmo salar L., held in freshwater, was evaluated as a preventative treatment against sea lice, Lepeophtheirus salmonis, following transfer of fish to seawater.

In the safety study, salmon smolts held in freshwater were fed with diets containing emamectin benzoate at nominal doses of 0 (control), 50 (recommended dose) and 250 (5× recommended dose) μg kg−1 fish day−1 for 7 days (days 0–6). Actual dose rates, based on measured concentrations of emamectin benzoate in feed, differences in fish weight, and feed consumed, were 0, 54, and 272 μg kg−1 day−1, respectively. On day 9, fish were transferred to seawater and observed for 14 days. No differences in feeding response, coordination, behaviour, gross and histological appearance were observed between control fish and those that received 54 μg kg−1 day−1. Among smolts that received 272 μg kg−1 day−1, approximately 50% exhibited darker coloration, and one fish (1%) exhibited uncoordinated swimming behaviour. No pathognomonic signs of emamectin benzoate toxicity were identified.

In the efficacy study, smolts held in freshwater were fed an unmedicated ration (control group) or emamectin benzoate at 50 μg kg−1 day−1 (treated group) for 7 days (days 0–6). On day 9, fish were re-distributed to eight seawater tanks, each holding 30 control and 30 treated fish. On days 28, 56, 77 and 109, respectively, control and treated fish in two tanks were challenged with L. salmonis copepodites. When lice in each group reached chalimus stage IV, fish were sampled and the numbers of lice were recorded. Fish challenged at day 109 were sampled for the second time when lice were at the adult stage. Efficacy was calculated as the reduction in the mean number of lice on treated fish relative to the mean on control fish. Treatment with emamectin benzoate resulted in an efficacy of 85.0–99.8% in fish challenged at days 28–77, from the start of treatment, and lice counts were significantly lower (P<0.001) on treated fish than on controls. When fish challenged at day 109 were sampled at day 128, efficacy was 44.3%, but survival of chalimus to adult lice on treated fish was lower, and at day 159, efficacy had increased to 73%. These results demonstrate that treatment of salmon smolts with emamectin benzoate in freshwater was well tolerated and highly effective in preventing sea lice infestation following transfer of fish to seawater.  相似文献   


10.
Comparison of nutrients release among some maricultured animals   总被引：6，自引：0，他引：6  
Integrated mariculture is a feasible method to maintain sustainable and high productivity of aquaculture. The choice of cultured animals and biofilters in the integrated system has to be made on the basis of their nutrient release rates and the clearance rate of each component of the system. We are examining the nutrient release rates among fish (mangrove snapper, Lutjanus russeli, and sea perch, Abudefduf septemfasciatus), abalone (Haliotis diversicolor), scallops (Chlamys noblis), and green mussels (Perna viridis) in the laboratory. Fish feed is the major sources of inorganic nutrient input in fish farms. The orthophosphate and ammonia release rates of minced trash fish (1593 μg P g−1 day−1 and 150 μg N g−1 day−1) were respectively 6–12 times and 4–88 times higher than those of cultivated fish. Mangrove snapper had the overall highest nutrient release rate, followed by sea perch, abalone, scallops, and mussels for nitrite and nitrate; and followed by abalone, sea perch, mussels, and scallops for orthophosphate and ammonium. Among mollusks, abalone had the highest orthophosphate (162 μg P g−1 day−1), nitrate (1.4 μg N g−1 day−1), nitrite (1.6 μg N g−1 day−1) and ammonium (25.0 μg N g−1 day−1) release rates per gram wet weight per day. Abalone released large amounts of orthophosphate, nitrite and nitrate in the experiment. Scallops and green mussels had low nutrient release rates.  相似文献   

11.
Nitrogen and phosphorus budgets were estimated in 12 indoor fiberglass tanks stocked with hybrid tilapia (Oreochromis niloticus×O. aureus) at densities of 1 kg, 5 kg, 10 kg and 15 kg/m3 and reared for 14 days. Each density was replicated three times, and the experiment was repeated five times. The water in each tank was changed daily. Fish were fed a 34% protein tilapia feed to satiation twice daily. Feed consumption rate significantly decreased (P<0.05) with increasing density, but the FCR did not vary significantly (P>0.05) among the treatments. The production of one kilogram of fish required 2.0–2.2 kg of feed in different stocking density treatments, while 87.1–95.6 g nitrogen and 12.6–13.8 g phosphorus were released into the water, as metabolic waste. Of the feed input, 21.4% of the nitrogen and 18.8% of the phosphorus were incorporated in the fish harvested.  相似文献   

12.
The 96-h LC50 of ammonia-N and the effects of dietary vitamin C on oxygen consumption, ammonia-N excretion and Na+/K+ ATPase activity of Macrobrachium nipponense exposed to ambient ammonia were investigated. The results showed that the 96-h LC50 of ammonia-N was 36.6 mg l−1 for the freshwater prawn, M. nipponense, at pH 8.0. When prawns were exposed to high ambient ammonia-N concentrations, the oxygen consumption rate increased and ammonia excretion decreased. Dietary vitamin C supplementation led to higher oxygen consumption and lower ammonia excretion. Na+/K+ ATPase activity increased with increased ambient ammonia-N exposure in the range of 0–18.3 mg l−1, and then was reduced at ambient ammonia-N 36.6 mg l−1. Na+/K+ ATPase activities of prawns fed a vitamin C-supplemented diet were significantly lower than those of prawns fed a diet which was not supplemented with vitamin C.  相似文献   

13.
Filtration rates of hatchery-reared king scallop (Pecten maximus L.) juveniles, fed a single species alga diet (Pavlova lutheri (Droop) Green), were measured at a range of temperatures (6–21 °C). Weight specific filtration rate (ml min−1 g−1 (live weight)) of juveniles of a selected size range of 17–19 mm shell height (0.26–0.36 g live weight) increased with temperature above 16 °C and decreased below 11 °C, but was not significantly different between these two temperatures. Measurements at 16 °C using juveniles with a wider size range of 10–25 mm shell height (0.05–0.8 g live weight) gave the allometric equation: filtration rate (ml min−1)=12.19×weight (g)0.887. Filtration rate decreased significantly when the cell concentration was greater than 200 cells μl−1 (4.25 mg (organic weight) l−1). With six other algae food species, filtration rates similar to those with P. lutheri were only achieved with Chaetoceros calcitrans (Paulsen) Takano. All other algae species tested were cleared from suspension at significantly lower rates. Experiments with diet mixtures of P. lutheri and these other algae suggested that this was usually a reflection of lowered filtration activity, rather than pre-ingestive rejection of cells. In experimental outdoor nursery rearing systems, the filtration rate was inversely proportional to the concentration of cells in the inflow, in the range 5–210 cells μl−1. It was not affected by flow rate (2–130 l h−1, equivalent to 0.12–28.38 l h−1 g−1 (live weight)) with scallop juveniles stocked from 2 to 62 g l−1. The results are discussed in relation to on-growing scallops at field sites.  相似文献   

14.
Florida red tilapia (Oreochromis sp.) were reared in 23 m3 seawater (37 ppt) pools. Monosex males (1.3 g mean weight) were stocked at a density of 25 fish/m3 and reared to fingerling size (>10 g) in pools receiving either chicken manure applied at a rate of 105 kg/ha day−1 or pelletized feed (30% protein) administered ad libitum. Following the nursery period, fingerlings in fed pools were reared through adult, marketable sizes.

After 20 days of nursery rearing, mean fish weights (5.7–9.6 g) and survival (77.5–98.6%) in manured pools ranged from less than to greater than values in fed pools (7.9–9.4 g and 95.5–98.2%). By day 33, while mean weights (11.3±0.4 g) and survival (84.5±5.2%) in manured pools were significantly less than those in fed pools (18.0±0.6 g and 95.9±1.4%), fingerling-size fish were obtained from manured pools at an overall productivity of 55 kg/ha day−1.

After 170 days in fed pools, mean fish weight was 467±9 g, survival was 89.7±0.9%, and food conversion was 1.6±0.2. Daily weight gain achieved a maximum of 4.4 g day before a rapid decline in water temperature from 28–29°C to 24–25°C caused a loss of fish appetite and evidence of disease.

The results suggest that while nursery rearing of Florida red tilapia in seawater pools fertilized with chicken manure is feasible, considerable variability in fish performance among pools can be expected, despite identical management methods. In pools receiving prepared feed, high growth rates and survival through adult, marketable sizes suggests a potential for commercial production of Florida red tilapia in seawater.  相似文献   


15.
The effect of an 80-day maintenance-feeding period on the acute stress response of common carp, Cyprinus carpio, to net confinement was determined. Fish were raised on an optimal feeding level of 20 g food/kg of metabolic fish weight per day (g/kg0.8 day−1) until 124 days post-hatch (dph). Feeding in group one (L>H) was then reduced to maintenance levels, i.e. 5 g/kg0.8 day−1 until 204 dph, when the feeding was again increased to 20 g/kg0.8 day−1. In group two (H>L), the feeding level was reduced from 20 to 5 g/kg0.8 day−1 on day 146. All fish were sampled at 226 dph. Food ration had significant effects on the growth rate and food conversion values with fish fed the high ration performing better than those on a lower level. Prior to the application of the stressor, only plasma levels of triglycerides were lower in fish fed a low food ration (H>L). Feeding history influenced the onset of the stress response with stressor-induced elevations of plasma cortisol, glucose and free fatty acids being higher in fish fed a high ration compared with those fed a low ration prior to sampling. These results suggest that feeding history through modification of the energy reserves can influence the onset of the acute stress response.  相似文献   

16.
Abstract.— Tilapia and freshwater prawn production in Puerto Rico for monoculture and polyculture systems were compared. The experiment consisted of three treatments with three replicates each. The stocking rates for the prawn monoculture, fish monoculture and polyculture treatments were respectively: 7 prawns/m2, 1 tilapia/M2, and 7 prawns with 1 tilapia/ m2. The mean stocking size for tilapia and prawn were respectively, 7–8 g and 1–1.3 g. After 145 d of culture, yields and mean weight of tilapia in monoculture and polyculture system were not significantly different. Total yields were 2,942 and 2,769 kg/ha, respectively. Mean weights were 348 g in monoculture and 331 g in polyculture. Yields and mean weight of prawns in monoculture and polyculture were significantly different. Total yields were 1,367 and 951 kg/ha, respectively. Mean weights were 55 g in monoculture and 31 g in polyculture. Total yield in polyculture was 3,720 kg/ha showing an increase over the production separately obtained in prawn and fish monoculture.  相似文献   

17.
In order to develop a simple and accurate index of the salinity resistance of tilapia, batches of 10 juveniles (5 to 20 g) of two different species Oreochromis niloticus and Sarotherodon melanotheron reared in freshwater were subjected to gradual increases in salinity until 100% mortality. Seven daily increments of salinity were tested with 4 replicates: 2, 4, 6, 8, 10, 12 and 14 g l−1 day−1, while control batches were kept in fresh water. The temperature was maintained at 27 °C. The concentration of oxygen, ammonia and the pH were not limiting factors. The mortality, monitored on a daily basis, appeared after 2–51 days and was spread out over 1–20 days, depending on the increment of salinity. The higher the daily rate in salinity increase, then the shorter the time lapse before total mortality occurred. The cumulative mortality as a function of salinity fit well with simple linear regressions. The criterion of the resistance to salinity was the index MLS (median lethal salinity) defined at each daily rate as the salinity at which 50% of fish died. For S. melanotheron, the mean MLS was 123.7±3.5 g l−1 whatever the daily rate in salinity. For O. niloticus, the MLS was 46.3±3.4 g l−1 for daily increases in salinity ranging from 2 to 8 g l−1 day−1 and decreased significantly (P<0.05) above this level. The MLS-8 g l−1 day−1 ,which takes into account the full capacity of the fish to adapt to the increasing salinity, appeared to be a simple, optimized and efficient criterion for assessing the resistance to salinity for O. niloticus and S. melanotheron. This criterion can be a useful tool for ranking the different parental strains and hybrids of different genus and species of tilapia used in programmes of genetic selection for growth and salinity tolerance.  相似文献   

18.
Growth performance, muscle cellularity and flesh quality were investigated in Atlantic salmon (Salmo salar L.) fed either of two diet ranges [high protein (HP), or low protein (LP)], which differed in digestible protein/digestible energy ratios but were of equivalent digestible energy content (21.4 MJ kg−1 wet weight). Smolts from an early maturing (Lochy) and a late maturing (Mowi) strain were PIT-tagged and reared together in duplicate 5×5×5-m sea cages for each diet. The Lochy and Mowi fish were harvested in May and August, respectively, after 417 and 515 days in seawater. The average body weight of fish in each cage at harvest was in the range 3.8–5.4 kg, with no significant difference between diets. The total cross-sectional area of white muscle and the number and diameter of muscle fibres was determined at the level of the first dorsal fin ray. The distribution of muscle fibre diameters was investigated using nonparametric smoothing and bootstrapping techniques. Diet had no effect on fibre size distribution or fibre number in the Mowi strain, and small but significant effects for the Lochy strain. At harvest, in Lochy salmon of average fork length 69 cm there were around 15% more fibres in fish fed the HP than LP ratio diets. However, the 50th percentile of fibre diameter was 20% greater in fish fed the LP than HP diets, such that the total muscle cross-sectional area was similar. The lipid content (14.1–15.3% wet mass), astaxanthin pigment concentration (7.0–8.5 mg kg−1 wet mass) and colour (RocheSalmoFan™ and Minolta Chromatometer readings) of the flesh were similar for both strains and diets. There was no significant difference in the average muscle fibre density between strains and diet, which varied between 60 and 140 fibres mm−2 muscle cross-sectional area. Gaping during processing of the fillet was in part related to muscle cellularity. Little or no gaping was observed in any fish with a fibre density in excess of 95 fibres mm−2 muscle. It was concluded that individual variation in fibre density is important in the development of gaping, but that muscle cellularity and flesh quality are relatively insensitive to the protein to energy ratio in the diet over the range studied.  相似文献   

19.
Fibreglass pools with sediment were used as model farming ponds to investigate the interactive effects of pond preparation and feeding rate on prawn production, water quality, bacterial dynamics, abundance of benthos and prawn feeding behaviour. Pools were either fertilised 1 month (prepared) or 2 days (unprepared) prior to stocking and either ‘high’ or ‘low’ feeding rates were used. The ‘high’ rate was 5.0% (range 4–8%) wet prawn biomass/day and was similar to that recommended for commercial farms. The ‘low’ rate was 2.5% (range 2–4%) wet prawn biomass/day. Juvenile Penaeus monodon (2.0–7.5 g) were stocked at 15 prawns/m2 and were cultured for 71 days. With the exception of one prepared, high feeding-rate pool where mass mortality (> 80%) of prawns occurred following an interruption to aeration, prawn survival was high (> 86%) and was unaffected by preparation, feeding rate or their interaction. Pond preparation improved growth and biomass gain by about 20%. Growth was 4% higher with the higher feeding rate but biomass gain was not affected and, as food conversion ratio was much worse, use of the lower feeding rate offers considerable scope to reduce production costs, especially during cooler periods. There was no interaction in relation to growth between pond preparation and feeding rate. Meiofauna were more abundant, and prawns grew faster, in prepared pools than unprepared pools at the start of the experiment. However, changes in bacterial dynamics or meiofauna abundance over time did not explain reductions in prawn growth over time. In general, water quality was reduced in pools receiving the high feeding rate compared with low feeding rate pools. Other interactive effects of pond preparation and feeding rate on water quality, bacteria, benthos and prawn feeding behaviour are discussed.  相似文献   

20.
Oxygen consumption rates of white sturgeon (Acipenser transmontanus) were measured under commercial culture conditions. Mean fish size ranged from 0.09 to 3.8 kg (0.2–8.4 lbs). Mean daily values of oxygen consumption rates ranged from 70–330 mg kg fish−1 h−1. Peak oxygen consumption rates were measured to be as much as twice the mean daily values and were seen to occur in response to feeding for fish fed a ration of less than 2.6% body mass per day. With higher feed rations, peak oxygen consumption rates were a smaller percentage of the mean daily value. Multiple regression analysis showed that 93% of the variations in measured oxygen consumption rate values could be attributed to variations in feed ration.  相似文献   

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