Evaluation of Low‐protein Alternative Diets for Pond‐raised Hybrid Catfish,Ictalurus punctatus × Ictalurus furcatus

A study was conducted to evaluate low‐protein traditional or alternative diets for pond‐raised hybrid catfish, Ictalurus punctatus × Ictalurus furcatus. Three 24% protein diets containing decreasing levels of soybean meal (30, 20, and 15%) and increasing levels of cottonseed meal and corn germ meal were compared with a 28% protein control diet. Hybrid catfish fingerlings (mean initial weight = 71 g/fish) were stocked into 20 earthen ponds (0.04 ha) at a density of 14,826 fish/ha with five ponds per dietary treatment. Fish were fed once daily to apparent satiation for a 191‐d growing season. There were no significant differences in total diet fed, net yield, weight gain, feed conversion ratio (FCR), survival, or fillet proximate nutrient composition among dietary treatments (P ≥ 0.10). However, regression analysis showed for fish fed 24% protein diets there was a linear increase in FCR as soybean meal levels decreased (P = 0.06). Compared with fish fed the 28% protein control diet, fish fed 24% protein diets had lower carcass and fillet yield. Results demonstrate a 24% protein alternative diet containing 20% soybean meal may be substituted for 28% protein diets for hybrid catfish during food fish production.     

Efficacy of Crystalline Lysine in Alternative Diets for Pond‐raised Hybrid Catfish, ♀ Ictalurus punctatus × ♂ Ictalurus furcatus

A study was conducted to examine the efficacy of crystalline lysine in alternative diets for pond‐raised hybrid catfish, ♀ Ictalurus punctatus × ♂ Ictalurus furcatus. Two 28% protein alternative diets supplemented with l ‐lysine HCl at the required level based on 62% (previously published value) or 100% lysine availability were compared with a traditional 28% protein control diet. Hybrid catfish fingerlings (mean initial weight = 43 g/fish) were stocked into 15 earthen ponds (0.04 ha) at a density of 14,826 fish/ha with five ponds per treatment. Fish were fed once daily to apparent satiation for a 173‐d growing season. There were no significant differences in total diet fed, net yield, weight gain, and survival among dietary treatments. There were also no significant differences in carcass yield, fillet yield, and fillet proximate composition and fillet lysine concentration among treatments. Fish fed the traditional control diet had slightly, but significantly, lower feed conversion ratio than fish fed alternative diets, which is likely related to higher dietary fiber levels in the alternative diets. Results from this study show that crystalline lysine can be considered 100% available when used to supplement lysine‐deficient diets for pond‐raised hybrid catfish.     

Pond‐raised Hybrid Catfish, ♀ Ictalurus punctatus × ♂ Ictalurus furcatus,Do Not Respond to Microbial Phytase Superdosing

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.     

Replacing Soybean Meal with Alternative Protein Sources in Diets for Pond‐raised Hybrid Catfish, ♀ Ictalurus punctatus × ♂ Ictalurus furcatus

The present study investigated the replacement of soybean meal with combinations of two or three alternative protein sources in diets for pond‐raised hybrid catfish, ♀ Ictalurus punctatus × ♂ Ictalurus furcatus. Alternative protein sources evaluated included cottonseed meal, distillers dried grains with solubles (DDGS), peanut meal, and porcine meat and bone meal (PMBM). Hybrid catfish fingerlings with a mean initial weight of 35 g/fish were stocked into 25 earthen ponds (0.04 ha) at a density of 14,826 fish/ha. Fish were fed once daily to apparent satiation for 166 d. No significant differences were observed for total diet fed, net yield, weight gain, survival, carcass yield, fillet yield, or fillet proximate composition among dietary treatments. Results show soybean meal may be completely replaced by combinations of cottonseed meal and one or two other alternative protein sources including DDGS, peanut meal, and PMBM in the diet without markedly affecting production and processing characteristics and fillet proximate composition of pond‐raised hybrid catfish. These alternative diets may be used during foodfish production when prices are favorable.     

Response of Pond‐raised Fingerling Hybrid Catfish, ♀ Ictalurus punctatus × ♂ Ictalurus furcatus,to Dietary Protein Concentrations and Sources

This study examined four experimental diets with different protein concentrations and sources for pond‐raised fingerling hybrid catfish, ♀ Ictalurus punctatus × ♂ Ictalurus furcatus. A 35% protein diet with fishmeal was used as the control diet. Test diets were 32 and 28% all‐plant‐protein diets and a 28% protein diet with porcine meat, bone, and blood meal. Small fingerlings with a mean initial weight of 2.9 g/fish were stocked into 20 earthen ponds (0.04 ha) at a density of 172,970 fish/ha. They were fed once daily to apparent satiation for 107 d. No significant differences were observed for total diet fed, gross yield, final weight, survival, or condition factor among dietary treatments. However, fish fed the 28 and 32% all‐plant‐protein diets had a significantly higher feed conversion ratio than fish fed the 35% protein diet with fishmeal. There were no significant differences in chlorophyll a and nitrite concentrations in the pond water, but ponds receiving the 35% protein diet had significantly higher ammonia than those receiving 28% protein diets. Economic analysis suggested potential cost savings by using low‐protein and all‐plant‐protein diets for hybrid catfish fingerling production.     

Evaluation of Corn Gluten Feed and Cottonseed Meal as Partial Replacements for Soybean Meal and Corn in Diets for Pond‐raised Hybrid Catfish,Ictalurus punctatus×I. furcatus

This study examined the use of corn gluten feed (CGF) and cottonseed meal (CSM) to partially replace soybean meal and corn in diets for pond‐raised hybrid catfish, Ictalurus punctatus×I. furcatus. Five 28% protein diets containing various combinations of CGF and CSM were evaluated. Fingerling hybrid catfish (mean initial weight: 45 g/fish) were stocked into 25, 0.04‐ha ponds at a rate of 14,826 fish/ha. Fish were fed once daily to apparent satiation for a 179‐d growing season. CGF at 30% of the diet (10% CSM) and a combination of CGF and CSM up to 25% each did not affect physical quality (percentages floatability and feed dust) of the diet. No significant differences were observed in total amount of diet fed, net yield, diet consumption, weight gain, feed conversion ratio (FCR), survival, and fillet proximate nutrient composition among fish fed various diets. Results show that hybrid catfish can utilize CGF at levels up to 30% of the diet (10% CSM), and a combination of CGF and CSM up to 25% each without significantly affecting growth, diet consumption, FCR, and fillet proximate nutrient composition. However, a combination of CGF and CSM at 20% each and above reduced carcass yield.     

Use of Corn Germ Meal in Diets for Pond‐Raised Channel Catfish,Ictalurus punctatus

Corn germ meal (CGM) is a by‐product of corn milling. On the basis of its nutrient composition and digestibility values, it appears to be a suitable ingredient for use in channel catfish, Ictalurus punctatus, diets. A study was conducted to examine the use of various levels of CGM in diets for pond‐raised channel catfish. Four 28% protein diets containing 0, 15, 25, and 35% CGM were evaluated. Fingerling channel catfish (mean initial weight: 71 g/fish) were stocked into 24, 0.04‐ha ponds at a rate of 14,826 fish/ha. Fish were fed once daily to apparent satiation for a 167‐d growing season. No significant differences were observed in total amount of diet fed, diet consumption per fish, net yield, weight gain, feed conversion ratio, survival, fillet yield, and fillet protein, fat, and moisture concentrations among fish fed diets containing various levels of CGM. Carcass yield decreased linearly as dietary CGM levels increased. Depending on prices, CGM can be used interchangeably with corn gluten feed in channel catfish diets as replacements for corn, wheat middlings, and soybean meal to reduce feed cost.     

Performance of Alternative Diets Containing Solvent‐Extracted Distillers Dried Grains with Solubles Compared to Traditional Diets for Pond‐Raised Channel Catfish,Ictalurus punctatus,and Hybrid Catfish,Ictalurus punctatus × Ictalurus furcatus

Two concurrent pond studies were initiated in April 2011 to evaluate feeds containing solvent‐extracted distillers dried grains with solubles (SE‐DDGS) in both 28 and 32% protein catfish feeds. Channel catfish, Ictalurus punctatus, were stocked in multiple‐batch production ponds at the University of Arkansas at Pine Bluff (UAPB) and hybrid catfish, ♀ Ictalurus punctatus × ♂ Ictalurus furcatus, in single‐batch production ponds at the National Warmwater Aquaculture Center (NWAC), Mississippi State University, Stoneville, Mississippi, USA. The experimental design was a 2 × 2 factorial with two protein levels (32 and 28% protein), with and without 20% SE‐DDGS. Fish were fed once daily to apparent satiation, and managed similarly to a commercial farm for 186 d at UAPB and 172 d at NWAC. For channel catfish, two‐way ANOVA showed significant effects of both protein level (28% being better than 32%) and protein source (20% SE‐DDGS diets being better than traditional diets) on yield, survival, total diet fed, and feed conversion ratio (FCR), due primarily to effects on the understocked fingerlings. Partial budget analysis suggested that the 28% protein diet with the 20% SE‐DDGS was preferred economically for the prevailing feed costs. For hybrid catfish, two‐way ANOVA did not show significant differences in total diet fed, yield, survival, and processing yields, but use of SE‐DDGS resulted in a lower FCR. Results showed that both channel and hybrid catfish can utilize 20% SE‐DDGS in the diet without adversely affecting production or processing characteristics.     

长薄鳅苗种培育技术总结

长薄鳅一般在晚上摄食，仔稚鱼期沿池壁四周分布，以后有钻洞行为，苗种阶段以浮游动物为食，日粮平均为5．08％，铒产系数14．18，不同阶段的体重日增重率分别为9．147％，2．006％，1．337％，苗种培育总成活率30．9％。     

Efficacy of a Live‐attenuated Edwardsiella ictaluri Oral Vaccine in Channel and Hybrid Catfish

This study evaluated the efficacy of an oral live‐attenuated Edwardsiella ictaluri vaccine against enteric septicemia of catfish (ESC) in channel and hybrid catfish. The vaccine was delivered one time orally by feeding fish a diet coated with an attenuated E. ictaluri isolate at four doses to deliver between 4 × 10⁶ to 3.2 × 10⁷ viable vaccine cells/g wet feed. Thirty‐five days postvaccination, control and vaccinated fish were challenged with virulent E. ictaluri and mortality was examined for 30 d postchallenge. Mortality of nonvaccinated hybrids (85%) and nonvaccinated channel catfish (73%) was similar but significantly greater than all groups of vaccinated fish. In channel catfish, a trend toward increasing mortality with decreasing dose was observed. Mortality of channel catfish vaccinated with the lowest dose (26.6%) was significantly higher than fish vaccinated with the highest dose (14.1%) but similar to fish vaccinated at the intermediate doses (17.5 and 19.4%). In contrast, mortality of four doses of vaccinated hybrid catfish was similar and ranged between 10.4 and 14.0%. The data demonstrate that the attenuated E. ictaluri vaccine at all four doses tested is effective at reducing ESC‐related mortalities in hybrid and channel catfish.     

Compensatory Growth of Pond-reared Hybrid Striped Bass, Morone chrysops × Morone saxatilis, Fingerlings

Compensatory growth (CG) or “catch‐up growth” is a period of super‐accelerated growth following a period of suboptimal conditions (i.e., lack of prey availability or overwintering). Little is known about the CG response in pond‐raised fish and whether hybrid striped bass (HSB), Morone chrysops × Morone saxatilis, might exhibit the rapid growth states or improvements in other production characteristics that may accompany the response. To evaluate the potential for CG in HSB culture, a 16‐wk growth trial in twelve 0.1‐ha earthen ponds was conducted. Approximately 2850 fish (mean weight ± SD = 3.2 g ± 1.1) were stocked into ponds and subjected to one of four cyclic feeding regimens. Treatment regimens included a control (0 wk, fed twice daily to apparent satiation) and cycles of 1, 2, or 4 wk of feed deprivation, followed by 1, 2, or 4 wk of feeding to apparent satiation. Fish in the 4‐wk feeding regimen were offered feed twice during the feed‐deprivation period (once every other week). Growth, specific growth rate (SGR), hepatosomatic index (HSI), intraperitoneal fat ratio, and condition factor (CF) were measured every other week, while overall growth, feed efficiency (FE) (FE = [weight gain/feed fed] × 100), and survival were calculated at the trial termination. The effect of these feeding regimens on water quality was examined by monitoring pH, turbidity, total ammonia nitrogen, nitrite–nitrogen, nitrate–nitrogen, soluble reactive phosphorus, and chlorophyll a weekly; total nitrogen and phosphorous biweekly; and dissolved oxygen and temperature twice daily. Cyclic feeding elicited CG; fish subjected to the 2‐wk regimen had a significantly higher SGR than 0‐wk controls during all but the final refeeding period. FE was higher for all fish in the cyclic regimens, although only FE for fish in the 2‐wk regimen was statistically greater (40%) than the controls. HSI was the most responsive measure and significantly decreased in the 2‐ and 4‐wk treatments during feed‐deprivation period and overcompensated during the refeeding period. CF also varied with feeding cycle and proved to be an effective nonlethal measure of predicting a CG response. No statistical differences in water quality parameters were observed. These data suggest that CG can be effectively induced in pond‐raised HSB and that the increase in FE warrants further research for practical application. Future pond studies with fingerling HSB fish should be conducted with emphasis on feed‐deprivation periods of 2 wk and refeeding periods of at least twice that of the feed‐deprivation period.     

Length–weight relationships for 21 coastal fish species of the Azores, north-eastern Atlantic

Length–weight relationships were estimated for 21 coastal fish species of the Azores, namely Abudefduf luridus, Bothus podas, Chromis limbata, Coris julis, Diplodus sargus, Echiichthys vipera, Gaidropsarus guttatus, Labrus bergylta, Mullus surmuletus, Phycis phycis, Pomatomus saltator, Sarda sarda, Scorpaena maderensis, Scorpaena notata, Seriola rivoliana, Serranus atricauda, Sparisoma cretense, Sphyraena viridensis, Synodus saurus, Thalassoma pavo and Trachinotus ovatus. Significant length–weight relationships were found for all species. Sexual dimorphism did not affect the length–weight relationships, except in the cases of S. cretense and C. julis. Length–length equations for converting size measurements (standard length (SL) and fork length (FL) to total length (TL)) are also presented for all fish species.     

Water Quality and Plankton Communities in Hybrid Catfish (♀ Channel Catfish,Ictalurus punctatus × ♂ Blue Catfish,Ictalurus furcatus) Ponds After Partial Fish Harvest

Twelve 0.4‐ha ponds were stocked with 10,000 hybrid catfish fingerlings in March 2015. Six ponds were partially harvested in August to remove fish larger than ～0.57 kg. All remaining fish were removed in October and November. Partial harvest of faster‐growing fish removed ～26% of the fish initially stocked; feeding rate (and therefore external nutrient loading) was reduced by about the same amount. However, reduced nutrient loading after partial fish harvest had no meaningful effects on water quality, phytoplankton biomass, phytoplankton and zooplankton community structure, or supplemental aeration. Lack of ecosystem change was caused by persistent internal recycling of nutrients added to the system before partial harvest and continued high (albeit reduced) external nutrient loading after partial harvest. Decisions to employ partial fish harvest to manage single‐cropped hybrid catfish ponds should be based on economic considerations and risk reduction rather than the expectation that fish biomass reduction will improve water quality.     

Costs of Winter Feeding of Channel‐blue (♀ Ictalurus punctatus × ♂ Ictalurus furcatus) Hybrid Catfish

Previous research has shown that winter feeding is beneficial in preventing weight loss and maintaining catfish health. Although several studies suggest the importance of winter feeding of channel catfish, Ictalurus punctatus, less is known about optimal winter feeding strategies for channel‐blue hybrid catfish (♀ Ictalurus punctatus × ♂ Ictalurus furcatus). Three winter feeding treatments (unfed, fed daily, and fed based on temperature‐threshold feeding) were each assigned randomly to four replicate 0.10‐ha earthen ponds. All ponds were stocked with large channel‐blue hybrid catfish (0.96 ± 0.40 kg) at the rate of 3409 kg/ha and fed using a slow‐sink 28% protein pelleted feed. The two feeding treatments showed significantly greater mean weight at harvest, gross yield, and growth rates than the unfed fish after the 113‐d winter trial. Partial budget analysis indicated that additional costs incurred from the additional feed, fuel, and labor costs over the winter in fed treatments offset the additional revenue from daily winter feeding. However, in the temperature‐threshold feeding treatment, additional costs were similar to additional revenues when 10‐yr average prices were used. Results were sensitive to feed prices and spring catfish prices with positive net benefits from winter feeding at fish prices above $1.58/kg and feed prices below $0.286/kg.     

Costs and Risk of Catfish Split‐pond Systems

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.     

The Influence of Ovarian Fluid pH of Stripped Unfertilized Channel Catfish,Ictalurus punctatus,Eggs on the Hatching Success of Channel Catfish ♀ x Blue Catfish,Ictalurus furcatus♂, Hybrid Catfish Eggs

This study was designed to determine the effect of ovarian fluid pH of stripped unfertilized channel catfish, Ictalurus punctatus, eggs on fertilization and hatch rate of channel catfish ♀ x blue catfish, Ictalurus furcatus♂, hybrid catfish eggs. A significant correlation was established between ovarian fluid pH of stripped channel catfish eggs and hybrid embryo hatch rate (R² = 0.75, P = 0.01), suggesting ovarian fluid pH of stripped catfish eggs prior to fertilization can be predictive of the hatching success of hybrid catfish embryos. These data were used to categorize pH of stripped eggs: pH <7.0 as “low pH eggs,” pH 7.0–7.4 as “medium pH eggs,” or pH >7.4 as “high pH eggs” quality eggs. The range in percent hatch rate for these pH categories was <15%, 15–30%, and >30%, respectively. Higher calcium concentrations during incubation do not appear to improve hatching success of “low pH eggs.” The predictive model presented herein describes a quick method for evaluating stripped catfish eggs for hybrid fry production in catfish hatcheries.     

Replacement of Fish Meal with Poultry By‐product Meal as a Protein Source in Pond‐raised Sunshine Bass,Morone chrysops ♀ × M. saxatlis ♂, Diets

Replacement of fish meal (FM) as a protein source with alternative sources of protein in aquaculture diets has been widely explored in aquaculture. The goal of replacement of FM in production diets is to maintain growth, lower production costs, and increase sustainability. Evaluation of the replacement of FM with poultry by‐product meal (PBM) in phase II sunshine bass diets, Morone chrysops × M. saxatilis, was conducted in ponds over 246 d. Four diets were formulated to be isonitrogenous (37%) and isocaloric (4 kcal/g) with different levels of FM replacement with PBM (0, 33, 67, and 100%, Diets 1–4, respectively). Twelve ponds were stocked with 400 phase II sunshine bass (mean weight 5.6 g) and randomly assigned one of the four diets. Fish were fed below satiation based on predicted growth and feed conversion, initially once daily (1700 h) and then twice daily (0700 and 1700 h) as water temperatures and feeding activity increased. Diets were evaluated based on production and performance indicators, body composition, and economic analysis. Production results revealed no significant differences in mean final individual fish weight (511 ± 21 g), net production (4257 ± 247 kg/ha), and survival (85 ± 2%). No significant differences occurred between the performance indicators: mean feed conversion ratio (2.47 ± 0.11), specific growth rate ( 1.84 ± 0.02), and protein conversion efficiency (23 ± 1.3%). Body composition was statistically similar for mean percent fillet weight (49 ± 0.6%) and percent intraperitoneal fat (9.8 ± 1.0%); however, the hepatosomatic index was significantly different between Diets 3 (3.7 ± 0.1%) and 4 (3.2 ± 0.1%). Mean proximate analysis of whole fish (dry weight basis) was not significantly different among treatments yielding the following: percent protein (46 ± 0.4%), lipid (47 ± 1.3%), and ash (8 ± 0.7%). Mean fillet composition (dry weight basis) also revealed no significant differences: percent protein (72 ± 0.8%), percent lipid (30 ± 1.6%), and percent ash (5 ± 0.2%). Proximate analysis was also performed on the diets and revealed a significantly lower protein content in Diet 3 (34.3 ± 0.5%) compared to the other diets (37.1 ± 0.4%). Amino acid analysis of the diets indicated a possible deficiency in methionine in Diets 3 and 4. Based on production, performance, and body composition, the results indicate that complete replacement of FM with PBM in sunshine bass diets is feasible; however, economic analysis suggests that the replacement of FM with PBM may result in reduced revenue over feed costs.     

Digestibility of Alternative Protein‐Rich Feedstuffs for Channel Catfish,Ictalurus punctatus

Apparent digestibility coefficients (ADCs) of amino acids, crude protein, gross energy, and dry matter of canola meal, corn gluten feed, fish offal meal, shrimp and fish offal meal, poultry by‐product meal, and hydrolyzed feather meal were determined for channel catfish, Ictalurus punctatus. Experimental diets contained 30% test ingredient, 69.5% casein‐based reference diet, and 0.5% chromic oxide. Groups of 20 fish (102.45 g) were fed the experimental diets twice a day at 3.5% body weight. Fecal samples were collected in triplicate daily at 0000 h and 0600 h after settlement into collection devices. Shrimp and fish offal meal and corn gluten feed presented significantly lower (P < 0.05) ADC for dry matter (59.5 and 39.3%) suggesting their low value as feedstuffs for catfish feeds. Although ADC values for crude protein were above 80% for all the test ingredients, amino acid digestibility varied significantly, except for histidine whose ADC remained constant regardless of the protein source. Lysine was the first limiting amino acid in most of the test ingredients, except in fish offal meal and poultry by‐product meal. Among the protein sources tested, only fish offal meal and poultry by‐product meal met channel catfish amino acid requirements for a 28% digestible protein grow‐out diet.     

Salt in the Food and Water as a Supportive Therapy for Ichthyophthirius multifiliis Infestation on Silver Catfish, Rhamdia quelen, Fingerlings

This study verified the efficacy of common salt (NaCl) in the food and water as a supportive therapy for Ichthyophthirius multifiliis and growth of silver catfish, Rhamdia quelen, fingerlings. After appearance of the first white spots following experimental exposure, indicating infestation by this parasite, fish were transferred to eighteen 40‐L polypropylene tanks and kept for 30 d. Experimental diets were prepared with five different levels of salt supplementation: 0.0, 1.2, 2.5, 5.0, and 6.0% for 30 d. In addition, another group of fish were fed a diet without salt supplementation but exposed to 4 g of salt/L of water. Fingerlings were collected at different times for analyses of whole‐body Na⁺, K⁺, and Cl^?. Dietary salt supplementation provoked a transitory increase in whole‐body Na⁺, K⁺, and Cl^? in infested catfish fingerlings, but the best stabilization of these ion levels was observed in specimens exposed to salt in the water. Silver catfish fed a diet containing 1.2% salt showed higher weight and biomass after 30 d compared to those fed with 6% salt. The use of 4 g of salt/L of water improved survival of infested silver catfish, but dietary salt supplementation was ineffective as a therapy for ichthyophthiriasis.     

Foodfish Production Strategies Using 13‐cm and 19‐cm Hybrid Catfish, ♀Ictalurus punctatus × ♂Ictalurus furcatus

Most hybrid catfish, ♀Ictalurus punctatus × ♂Ictalurus furcatus, producers stock 18‐ to 19‐cm fingerlings in single‐batch production. While stocking smaller fingerlings would be less expensive, the economic trade‐offs of using smaller fingerlings is unknown. Two sizes of hybrid catfish fingerlings (13‐cm and 19‐cm) were stocked in single‐size treatments at 9884 head/ha and a multi‐size treatment with each size stocked at 9884 head/ha (total 19,768 head/ha). In the 13‐cm and 19‐cm single‐size treatments, 87 and 98%, respectively, reached market size in one season. In the multi‐size treatment, 77% of all fish stocked reached market size, demonstrating that more than half of the 13‐cm fish reached market size in this treatment. Gross, net, and marketable yields were significantly greater in the multi‐size treatment when compared to the 13‐cm or 19‐cm single‐size treatments, but were not significantly different between the two single‐size treatments. The 19‐cm single‐size treatment resulted in greater break‐even prices and economic risk than the other two treatments. This study demonstrated that 13‐cm hybrid catfish fingerlings can be raised economically in both single‐ and multi‐size production systems in the southern USA.