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1.
Intensive production of ictalurid catfish in the USA has increased over the past several years, and a better understanding of the amount of organic carbon (OC) and dissolved oxygen (DO) in these culture environments is needed. Budgets for OC and DO were estimated over a production season (March to November) for an in‐pond raceway system for channel catfish, Ictalurus punctatus, and hybrid catfish (channel catfish × blue catfish, Ictalurus furcatus), with co‐culture of paddlefish, Polyodon spathula, and Nile tilapia, Oreochromis niloticus. Feed input ranged from 45 to 263 kg/ha/d with an overall average of 80 kg/ha/d. Production of each kilogram of live catfish required 1.5 kg of feed and released into the water 0.70 kg of OC, and led to the synthesis of an additional 3.36 kg of OC by photosynthesis. Consequently, production of 1 kg of live catfish resulted in 4.06 kg OC, and harvest of catfish accounted for only 29.5% of OC applied from the feed. Removal of OC increased to 34.3% with the additional harvest of paddlefish and tilapia. OC was consumed in respiration, and some OC accumulated in sediment. Total respiration within the system exceeded the DO produced by photosynthesis, while diffusion and mechanical aeration aided in maintaining suitable DO levels for fish production.  相似文献   

2.
Diets containing 28% and 32% crude protein were compared for pond‐raised channel catfish Ictalurus punctatus stocked at densities of 14,820, 29,640, or 44,460 fish/ha. Fingerling channel catfish with average initial weight of 48.5 g/fish were stocked into 30 0.04‐ha ponds. Five ponds were randomly allotted for each dietary protein ± stocking density combination. Fish were fed once daily to satiation for two growing seasons. There were no interactions between dietary protein concentration and stocking density for any variables. Dietary protein concentrations (28% or 32%) did not affect net production, feed consumption and weight gain per fish, feed conversion ratio, survival, processing yields, fillet moisture, protein and ash concentrations, or pond water ammonia and nitrite concentrations. Fish fed the 32% protein diet had slightly but significantly lower levels of visceral and fillet fat than fish fed the 28% protein diet. As stocking density increased, net production increased, while weight gain of individual fish, feed efficiency, and survival decreased. Stocking densities did not affect processing yield and fillet composition of the fish. Although highly variable among different ponds and weekly measurements, ponds stocked at the highest density exhibited higher average levels of total ammonia‐nitrogen (TAN) and nitrite‐nitrogen (NO2‐N) than ponds stocked at lower densities. However, stocking density had no significant effect on un‐ionized ammonia‐nitrogen (NH3‐N) concentrations, calculated based on water temperature, pH, and TAN. By comparing to the reported critical concentration, a threshold below which is considered not harmful to the fish, these potentially toxic nitrogenous compounds in the pond water were generally in the range acceptable for channel catfish. It appears that a 28% protein diet can provide equivalent net production, feed efficiency, and processing yields as a 32% protein diet for channel catfish raised in ponds from advanced fingerlings to marketable size at densities varying from 14,820 to 44,460 fish/ha under single‐batch cropping systems. Optimum dietary protein concentration for pond‐raised channel catfish does not appear to be affected by stocking density.  相似文献   

3.
To quantitatively define relationships among stocking densities, feeding rates, water quality, and production costs for channel catfish, Ictalurus punctatus, grown in multiple‐batch systems, twelve 0.1‐ha earthen ponds were stocked at 8,600, 17,300, 26,000, or 34,600 fingerlings/ha along with 2,268 kg/ha of carryover fish. Fish in all ponds were fed daily to apparent satiation using 32% protein floating feed. Temperature and dissolved oxygen in each pond were monitored twice daily; pH weekly; nitrite‐N, total ammonia nitrogen, and Secchi disk visibility every 2 wk; nitrate‐N, chlorophyll a, total nitrogen, total phosphorus, and chemical oxygen demand monthly; and chloride every other month. The costs of producing channel catfish at different stocking densities were estimated. There were no significant differences (P > 0.05) as a result of stocking density among treatment means of (1) gross or net yields, (2) mean weights at harvest, and (3) growth or survival of fingerlings (24–36%) and carryover fish (77–94%). Mean and maximum daily feeding rates ranged from 40 to 53 kg/ha/d and 123 to 188 kg/ha/d, respectively, and feed conversion ratios averaged 1.75. There were no differences in any feed‐related parameter as a result of density. Water quality variables showed few differences among densities at samplings and no differences when averaged across the production season. Yield of fingerlings increased as stocking density increased with significant differences between the two highest and the two lowest stocking densities. Breakeven prices were lower at the higher stocking densities as a result of the higher yield of understocked fish and similar mean individual fish weights produced at these higher stocking densities. Overall, varying stocking densities of fingerlings in multiple‐batch systems had little effect on production efficiency and water quality. Additional research on managing the population structure of carryover fish in commercial catfish ponds may be warranted.  相似文献   

4.
Two experiments were conducted in consecutive years to evaluate the responses of hybrid catfish, ♀ Ictalurus punctatus × ♂ Ictalurus furcatus, to “superdosing” of 6‐phytase added to existing commercial catfish feeds. In each experiment, two diets with or without a phytase superdose (2500 and 5000 phytase units/kg, respectively) were compared. In Experiment 1, fingerlings (mean weight: 59 g/fish) were stocked in 17 0.4‐ha earthen ponds at 17,290 fish/ha and were fed once daily to apparent satiation for 198 d. In Experiment 2, fingerlings (mean weight: 47 g/fish) were stocked in 10 0.4‐ha ponds at 24,710 fish/ha and were fed for 128 d. In both experiments, there were no significant differences in total feed fed, gross yield, final fish weight, survival, or Blood packed cell volume between fish fed diets with or without phytase. The diets also had no significant effects on pond water column total phosphorus or chlorophyll a concentrations, but soluble reactive phosphorus concentrations were significantly higher in ponds receiving the phytase diet in Experiment 2. Phytase superdosing of nutritionally complete feeds does not appear to have additional benefits beyond the standard phytase dose on production characteristics or packed cell volume of pond‐raised hybrid catfish and had no beneficial effects on water quality.  相似文献   

5.
An environmental assessment was made of Alabama channel catfish Ictalurus punctatus farming which is concentrated in the west‐central region of the state. There are about 10,000 ha of production ponds with 10.7% of the area for fry and fingerlings and 89.3% for food fish. Food fish production was about 40,800 tons in 1997. Watershed ponds filled by rainfall and runoff make up 76% of total pond area. Water levels in many of these ponds are maintained in dry weather with well water. The other ponds are embankment ponds supplied by well water. Harvest is primarily by seine‐through procedures and ponds are not drained frequently. The main points related to Alabama catfish farming and environment issues are as follows: 1) catfish farming in Alabama is conservative of water, and excluding storm overflow, about two pond volumes are intentionally discharged from each pond in 15 yr; 2) overflow from ponds following rains occurs mostly in winter and early spring when pond water quality is good and stream discharge volume is high; 3) total suspended solids concentrations in pond effluents were high, and the main sources of total suspended solids were erosion of embankments, pond bottoms, and discharge ditches; 4) concentrations of nitrogen and phosphorus in effluents were not high, but annual effluent loads of these two nutrients were greater than for typical row crops in Alabama; 5) ground water use by the industry is about 86,000 m3/d, but seepage from ponds returns water to aquifers; 6) there is little use of medicated feeds; 7) copper sulfate is used to control blue‐green algae and off‐flavor in ponds, but copper is rapidly lost from pond water; 8) although sodium chloride is applied to ponds to control nitrite toxicity, stream or ground water salinization has not resulted from this practice; 9) fertilizers are applied two or three times annually to fry and fingerling ponds and occasionally to grow‐out ponds; 10) hydrated lime is applied occasionally at 50 to 100 kg/ha but this does not cause high pH in pond waters or effluents; 11) accumulated sediment removed from pond bottoms is used to repair embankments and not discarded outside ponds; 12) sampling above and below catfish pond outfalls on eight streams revealed few differences in stream water quality; 13) electricity used for pumping water and mechanical aeration is only 0.90 kW h/kg of production; 14) each metric ton of fish meal used in feeds yields about 10 tons of dressed catfish. Reduction in effluent volume through water reuse and effluent treatment in settling basins or wetlands does not appear feasible on most farms. However, some management practices are recommended for reducing the volume and improving the quality of channel catfish pond effluents.  相似文献   

6.
Proliferative gill disease (PGD) in catfish is caused by the myxozoan Henneguya ictaluri. The complex life cycle requires Dero digitata as the oligochaete host. Efforts to control PGD by eradicating D. digitata have been unsuccessful. Smallmouth buffalo, Ictiobus bubalus, (SMB) are opportunistic bottom feeders and a putative option for controlling D. digitata. In 2011, 15 ponds (0.4 ha) were stocked with 5000 channel catfish, Ictalurus punctatus; 7 of these 15 ponds were also stocked with 300 SMB fingerlings. There were no differences in benthic invertebrate numbers or water quality variables between ponds with or without SMB. At harvest, there were no differences in percent survival, total weight, or catfish feed conversion ratio. In the second year, 18 ponds (0.4 ha) were stocked with 6000 channel catfish. Half the ponds were also stocked with 300 SMB. Sentinel fish were used to estimate disease severity, and pond water was collected for molecular estimation of H. ictaluri actinospore concentrations. Similar to the first year, there were no differences between treatments in any variable tested, including PGD severity in sentinel fish and parasite concentrations in pond water. Under these study conditions, presence of SMB did not have a measureable effect on PGD incidence, parasite density, or overall catfish production.  相似文献   

7.
Sediment samples were collected from 42 catfish (Clarias hybrid) ponds, 40 freshwater prawn (Macrobrachium rosenbergii) ponds and 18 carp (Puntius spp.) ponds in Thailand. Regression analysis revealed that pond age (1–30 years) was not a major factor influencing the physical and chemical composition of pond sediments. Sediment depth, F+S horizon thickness and bulk density of S horizon were greater (P<0.05) in carp ponds than in catfish and prawn ponds. This occurred because sediment was removed from catfish and prawn ponds more frequently than from carp ponds. Total carbon, organic carbon and total nitrogen concentrations were greater (P<0.05) in carp ponds than prawn and catfish ponds. Few ponds had sediment organic carbon concentrations above 3%, and carbon:nitrogen ratio values did not differ (P>0.05) among ponds for the three species. Total phosphorus and other sediment phosphorus fractions increased in the order prawn ponds, carp ponds and catfish ponds. Sediment sulphur concentrations also increased in the same order. There were no differences in major or minor nutrient concentrations in sediment that would influence aquacultural production. Although there were significant correlations (P<0.05) between various sediment quality variables, no single variable or group of variables would be useful in estimating sediment quality. Pond bottom management practices used by producers in Thailand included drying of pond bottoms between crops, liming, tilling and periodic sediment removal. These practices have maintained relatively good bottom quality. They should be continued in Thailand and adopted in other places.  相似文献   

8.
Channel catfish Ictalurus punctatus farming is the largest component of aquaculture in the USA. Culture technologies have evolved over time, and little recent work has been conducted on the effects of stocking density on production characteristics and water quality. Twelve 0.1‐ha ponds were stocked with 13‐ to 15‐cm fingerlings (16 g) at either 8600, 17,300, 26,000, or 34,600 fish/ha in single‐batch culture with three replicates per treatment. Fish were fed daily to apparent satiation with a 32% floating commercial catfish feed. Nitrite‐N, nitrate‐N, total ammonia nitrogen (TAN), total nitrogen, total phosphorus, chemical oxygen demand (COD), Secchi disk visibility, chlorophyll a, chloride, total alkalinity, total hardness, pH, temperature, and dissolved oxygen (DO) were monitored. Ponds were harvested after a 201‐d culture period (March 26, 2003 to October 13, 2003). Net yield increased significantly (P < 0.05) as stocking density increased, reaching an average of 9026 kg/ha at the highest density. Growth and marketable yield (>0.57 kg) decreased with increasing stocking density. Survival was not significantly different among densities. Mean and maximum daily feeding rates increased with density, but feed conversion ratios did not differ significantly among treatments (overall average of 1.42), despite the fact that at the higher stocking densities, the feeding rates sometimes exceeded 112 kg/ha per d (100 lb/ac per d). Morning DO concentrations fell below 3 mg/L only once in a 34,600 fish/ha pond. Concentrations of chlorophyll a, COD, nitrite‐N, and TAN increased nominally with increasing feed quantities but did not reach levels considered problematic even at the highest stocking densities. Breakeven prices were lowest for the highest stocking density even after accounting for the additional time and growth required for submarketable fish to reach market size. While total costs were higher for the higher density treatments, the relatively higher yields more than compensated for higher costs.  相似文献   

9.
Global averages were obtained for amounts of energy, land, water, wildfish, nitrogen, and phosphorus embodied in aquaculture feed ingredients. These data allowed amounts of these embodied resources to be calculated for typical feed formulations for channel catfish, Ictalurus punctatus; hybrid catfish, I. punctatus♀ × I. furcatus♂; Vietnamese catfish, Pangasius spp.; Atlantic salmon, Salmo salar; rainbow trout, Oncorhynchus mykiss; tilapia, Oreochromis spp.; whiteleg shrimp, Litopenaeus vannamei; and black tiger shrimp, Penaeus monodon. Embodied resource use per m.t. of feed varied among species: energy, 4.90–12.48 GJ/m.t.; land, 0.082–0.312 ha/m.t.; water, 502–1227 m3/m.t.; wildfish, 0–2880 kg/m.t.; nitrogen, 3.08–8.63 kg/m.t.; phosphorus, 1.16–5.62 kg/m.t. These calculations did not account for variations in site‐specific factors related to embodied resources and feed composition and use. But they suggest that reducing feed conversion ratio (FCR) by 0.1 unit for the seven species (species groups) could potentially reduce feed use by around 1.1 million tonne (Mt) while conserving 9.8 million GJ of energy, 270,000 ha of agricultural land, 1.4 billion m3 of freshwater, and 1.24 Mt of wildfish. Reduction of the FCR is a powerful means of lessening farm‐level production costs and negative impacts of feed production and use.  相似文献   

10.
Growth and yield (kg ha?1) of the channel catfish (Ictalurus punctatus, Rafinesque, 1818) and the channel × blue hybrid catfish [I. punctatus female ×I. furcatus (Lesueur, 1840) male], which shared the Jubilee strain of channel catfish as the maternal parent, were compared in sixteen 0.1 ha earthen ponds (14 852 fish ha?1) during the April to November growing season. Each fish genetic group was fed a commercially formulated 32% protein feed daily to apparent satiation or at 80% of the mean daily satiation ration. Net yield and individual weight were higher for channel × blue hybrid catfish compared with channel catfish and for fish fed a full ration compared with a restricted ration. When fed a full ration, the channel × blue hybrid catfish grew faster from May to September than did the purebred channel catfish because the hybrid catfish consumed a greater percentage of its body weight at each feeding. Net yield within each fish genetic group was lower when feed ration was restricted. The per cent reduction in net yield in response to feed restriction was similar for each fish genetic group.  相似文献   

11.
A 2 ± 4 factorial experiment was conducted to examine effects of dietary protein level (28, 32, 36, and 40%) and feeding rate (satiation or ± 90 kg/ha per d) on production characteristics, processing yield, body composition, and water quality for pond-raised channel catfish Ictalurus punctatus. Fingerling channel catfish with a mean weight of 64 g/fish were stocked into 40 0.04-ha ponds at a rate of 17,290 fish/ha. Fish were fed once daily to apparent satiation or at a rate of ± 90 kg/ha per d for 134 d during the growing season. Dietary protein concentration had no effect on feed consumption, weight gain, feed conversion, survival, aeration time, or on fillet moisture, protein, and fat levels. Fish fed to satiation consumed more feed, gained more weight, had a higher feed conversion, and required more aeration time than fish fed a restricted ration. Visceral fat decreased, and fillet yield increased as dietary protein concentration increased to 36%. Carcass yield was lower for fish fed a diet containing 28% protein. Increasing feeding rate increased visceral fat but had no major effect on carcass, fillet, and nugget yields. Fish fed to satiation contained less moisture and more fat in the fillets that those fed a restricted ration. Nitrogenous waste compounds were generally higher where the fish were fed the higher protein diets. Although there was a significant interaction in pond water chemical oxygen demand between dietary protein and feeding rate, generally ponds in the satiation feeding group had higher chemical oxygen demand than ponds in the restricted feeding group. There was a trend that pond water total phosphorus levels were slightly elevated in the satiation feeding group compared to the restricted feeding group. However, pond water soluble reactive phosphorus and chlorophyll-a were not affected by either diet or feeding rate. Results from the present study indicate that a 28% protein diet provides the same level of channel catfish production as a 40% protein diet even when diet is restricted to 90 kg/ha per d. Although there was an increase in nitrogenous wastes in ponds where fish were fed high protein diets, there was little effect on fish production. The long term effects of using high protein diets on water quality are still unclear. Feeding to less than satiety may be beneficial in improving feed efficiency and water quality.  相似文献   

12.
Three experiments were conducted to evaluate the need for supplemental phosphorus in the diet of channel catfish Ictalurus punctatus as well as to compare dicalcium phosphate and defluorinated phosphate as sources of supplemental phosphorus. Fingerling channel catfish were stocked into 0.04-ha earthen ponds at a rate of 1,000 fish/pond (24,700ha). The fish were fed a feed typical of commercial catfish feeds containing 28% protein and 2.8 kcal digestible energy/g once daily to satiation during the growing season (April to October). Fish in experiment 2 were overwintered and fed at a rate of 1% body weight twice weekly when the water temperature exceeded 13 C. The basal diet used in experiments 1 and 2, which contained no supplemental phosphorus, had estimated available phosphorus concentrations of 0.26 and 0.20%, respectively. Dicalcium phosphate was added to provide available phosphorus concentrations of 0.34 and 0.41% for experiment 1, and 0.27 and 0.35% for experiment 2. Diets used in experiment 3 to compare dicalcium and defluorinated phosphates contained 0.40% available phosphorus. Data from experiments 1 and 2 indicated that a concentration of dietary phosphorus of about 0.27% was adequate for maximum weight gain and efficient conversion of feed by channel catfish. However, a concentration of about 0.35% available phosphorus was required for maximum bone mineralization in experiment 2. There were no differences in growth or bone mineralization between fish fed dicalcium or defluorinated phosphate. We conclude that the small increase in bone phosphorus (about 4%) is biologically insignificant, and suggest that 0.3% available phosphorus be adequate for channel catfish raised in earthen ponds. Also, either dicalcium or defluorinated phosphate can be used as a source of supplemental phosphorus in channel catfish diets. However, defluorinated phosphate may be desirable because of its low solubility in water.  相似文献   

13.
Direct use of pig wastes as inputs into fish culture systems may be unacceptable or an inferior use of valuable inputs. High value, but non-filter feeding fish, such as African catfish, Clarias gariepinus (Burchell), may be unable to recover nutrients efficiently through the pond food web and require complete diets in intensive culture. Live feeds such as the larval stage of the green blow fly. Lucilia sericata, can be used as intermediate organisms to utilize pig waste and subsequently be fed live as part of a complete ration for catfish raised in cages. The nutrient efficiency of the system is further enhanced by the stocking of phytophagous fish, the Nile tilapia, Oreochromis niloticus (L.), in the pond in which the catfish culture cages are suspended. A model derived from on-farm experimentation is presented that demonstrates system design and nutrient efficiencies. An extrapolated catfish production of 61 year1 using only fly larvae produced from a standing herd of approximately 1000 fattening pigs was demonstrated. The static water pond in which the catfish were cultured ensured that the environmental impact of both pig and catfish systems was minimal compared to conventional production systems.  相似文献   

14.
采用低频率运转循环水处理系统(含粗滤器、臭氧仪、气液混合器,蛋白分离器、暗沉淀池等)联用池内设施(微泡曝气增氧机与净水网)开展凡纳滨对虾室内集约化养殖实验。研究了养虾池以水处理系统调控水质效果及氮磷收支。结果表明,养虾水经系统处理后,NO2-N(53.4%～64.5%)、CODMn(53.4%～94.4%)与TAN(31.6%～40.4%)被显著去除,有效改进虾池水质;养殖周期内未换水与用药,虾池主要水化指标均控制在对虾生长安全范围,7号实验池(100 d)与8号对照池(80 d)主要水化指标变化范围:DO分别为 5.07～6.70 mg/L和4.38～6.94 mg/L,TAN 0.248～0.561 mg/L和0.301～0.794 mg/L,NO2-N 0.019～0.311 mg/L和0.012～0.210 mg/L,CODMn 10.88～21.22 mg/L和11.65～23.34 mg/L。7号池对虾生长指数优于8号池(80 d虾病暴发终止),单位水体产量分别为1.398 kg/m2与0.803 kg/m2。氮磷收支估算结果:7号与8号池饲料氮磷分别占总收入:氮93.70%与92.37%,磷98.77%与99.09%;初始水层与虾苗含氮共占总收入6.30%与7.63%,磷共占1.23%与0.91%。总水层(含排污水)氮磷分别占总输出:氮56.45%与59.86%,磷53.26%与55.79%;收获虾体氮磷分别占总输出:氮37.07%与31.94%,磷21.37%与13.11%。7号池饲料转化率较高;池水渗漏与吸附等共损失氮磷分别占总输出:氮7.00%与9.34%,磷25.37%与31.10%。实验结果表明,虾池以低频率运转循环水处理系统联用池内设施可有效控制水质与虾病,具较高饲料转化率。  相似文献   

15.
Fillets of channel catfish, Ictalurus punctatus, from three geographic areas, fillets of hybrid catfish (♀ I. punctatus × ♂ blue catfish, Ictalurus furcatus) from one of the areas, water samples from the culture ponds, and feed samples were subjected to elemental analysis by inductive‐coupled plasma atomic emission spectrometry (ICP‐AES). The fillets were low in concentrations of several elements, and ICP‐AES could consistently detect only 11 elements. In addition, the composition of the fillets was not greatly influenced by water chemistry or feed composition. Nevertheless, both canonical discriminant analysis and K‐nearest‐neighbor analysis were reliable in separating the fillets to geographic area of origin and separating hybrid from channel catfish fillets based on elemental composition. Although this study suggests that multielement analysis and pattern recognition techniques have potential for validating the geographic origin of catfish fillets, much more work is needed to perfect the technique .  相似文献   

16.
Split ponds are recently developed pond‐based aquaculture systems that allow intensification of catfish aquaculture. Successful industry‐wide adoption of newly developing technologies like split‐pond systems will depend upon their productivity and cost efficiencies. Costs and production performance of the following three split‐pond design scenarios were monitored in Arkansas and Mississippi: (1) research design developed at the Thad Cochran National Warmwater Aquaculture Center, Stoneville, Mississippi; (2) waterwheel design tested on commercial catfish ponds; and (3) screw‐pump design tested on commercial catfish ponds. An economic engineering approach using standard enterprise budget analysis was used to develop estimates of breakeven prices (BEPs) ($/kg) for producing foodsize hybrid catfish (♂Ictalurus furcatus × ♀Ictalurus punctatus) for each scenario. Estimates of BEPs of hybrid catfish raised in split ponds ranged from $1.72 to $2.05/kg. The cost of catfish production in split ponds was sensitive to yield, fish prices, and feed prices. Annual net cash flows from both commercial split‐pond systems were high and sufficient to make the investment profitable in the long run. Feed price, feed conversion ratio, and yield contributed the most to downside risk of split ponds.  相似文献   

17.
The effect of Chinese waterchestnut (Eleocharis dulcis) on production of channel catfish (Ictalurus punctatus) and resulting water quality were studied in 1975 in 0.04-ha earthen ponds at Clemson University. Ponds containing waterchestnut had significantly lower levels of nitrate nitrogen and ammonia nitrogen. These lower nitrient levels resulted in lower phytoplankton levels in ponds with waterchestnut.Data indicated that Chinese waterchestnut had no effect on channel catfish production. Poor fish survival may have prevented detection of any effect of waterchestnut on catfish production.Chinese waterchestnut removed nutrients from the pond water. Mean nutrient removal per ha for the 201-day growing season was 108.06 kg of nitrogen, 6.90 kg of calcium, and 37.46 kg of magnesium. Mean corm production was 4664 kg per ha. These data indicate that Chinese waterchestnut should remove nutrients in sufficient quantities to improve water quality and allow increases in feeding rates and greater catfish production.  相似文献   

18.
Bolbophorus damnificus was recognized as a threat to channel catfish, Ictalurus punctatus, production in Louisiana and Mississippi in 1997 and 1999, respectively. Severe to moderate outbreaks (≥34% prevalence) are correlated to heavy losses, but impact of mild outbreaks with low prevalence (<33%) was unknown. Laboratory and field studies were conducted to evaluate sublethal acute (early stage) and chronic (late stage) trematode infection impacts on catfish production. Fish raised in ponds seeded with ram's horn snails from ponds harboring active B. damnificus outbreaks resulted in infection prevalence ranging from 1.6 to 20.4%. Compared to fish raised in ponds not seeded with infected snails (0% prevalence), fish biomass, number harvested, and total feed fed were significantly lower. These data agree with previous studies where mild infections reduced feed consumption, fish production, and economic returns. Infected fish were collected from ponds and used in a laboratory growth study. Once removed from the infection source, weight gain, growth rate, feed consumption, and feed efficiency were equal to or greater than trematode‐free fish. This suggests that although early B. damnificus infection (premetacercarial development) can severely impact production, infection has little impact on performance once metacercarial cysts are fully developed, and the infection source is removed.  相似文献   

19.
A length–weight relationship was developed for pond‐raised hybrid catfish fingerlings, Ictalurus punctatus × Ictalurus furcatus. A total of 4663 fish were sampled ranging from 20 to 240 mm total length. Predicted weight (g) from length (mm) is based on the equation: Y = 0.000017311X2.868474309 (r2 = 0.996) where Y is the estimated individual fish weight and X is measured total length. The predicted values generated by this model differ from, but follow the same general trends seen with channel catfish, I. punctatus, fingerlings and can be used as a baseline for the development of a length–weight table for hybrid catfish fingerling production.  相似文献   

20.
We compared production variables between channel catfish, Ictalurus punctatus, nursery ponds fed according to industry standards, that is feeding immediately at stocking, to an alternative practice of delaying feeding for 6 wk after stocking in an effort to utilize natural pond productivity and reduce feed use. Twelve 0.04 ha ponds were fertilized and stocked with swim‐up fry (4–5 d posthatch) at a rate of 10,000/pond (250,000/ha). Ponds were then randomly assigned to either the standard feeding protocol (feeding daily starting immediately at stocking) or an alternative feeding protocol (no feeding until 6 wk post‐stocking). After 18 wk of production, there were no differences in water quality or zooplankton abundance between the two treatments. Fish length was not affected by treatment throughout the study, and survival and total weight harvested were similar. Total kg of feed fed was significantly reduced in the delayed feed treatment, averaging 26 kg/pond less feed fed. If proper fertilization practices are implemented, large numbers of desirable zooplankton for catfish fry culture are attained, and these zooplankton are able to sustain catfish fry stocked up to 250,000/ha. Therefore, no commercial diets are required during the first 6 wk of culture, saving over $95.55/ha in initial feed costs.  相似文献   

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