Phosphorus Budgets for Channel Catfish Ponds Receiving Diets with Different Phosphorus Concentrations

Phosphorus budgets were prepared for channel catfish Ictalurus punctatus ponds at Auburn, Alabama, that received one of five diets ranging from 0.60 to 1.03% phosphorus. Fish production did not differ ( P > 0.05) among diets. There were few differences among treatments with respect to soluble reactive phosphorus, total phosphorus, and chlorophyll a concentrations or gross primary productivity. Phosphorus loss in effluents when ponds were drained for harvest did not differ among treatments ( P > 0.05). Phosphorus removed from ponds in fish at harvest and the amounts of phosphorus adsorbed by bottom soils increased as dietary phosphorus concentration increased (P < 0.05). Low-phosphorus diets did not decrease phytoplankton productivity or improve effluent quality. Uptake of phosphorus by bottom soils is a major factor controlling phosphorus concentrations in pond water. Low-phosphorus diets can be beneficial in catfish pond management by reducing the phosphorus load to bottom soils and conserving their ability to adsorb phosphorus.     

Salt Discharge from an Inland Farm for Marine Shrimp in Alabama

The total salt input in saline well water, mineral amendments, feed, and rainfall and runoff to ponds of an inland shrimp farm in Alabama was 1980.8 tonnes over a 5‐yr period. A residual of 270.4 tonnes of salt remained in pond water and 38.3 tonnes in bottom soil. Only 8.0 tonnes of salt were removed in harvested shrimp. A total of 1588.0 tonnes of salt or 80.2% of the input was lost to the environment with about equal amounts exiting the ponds in seepage and in overflow and harvest effluent. About 4.2% of the salt input (84.1 tonnes) could not be accounted for because of errors in assumptions and measurements. Salt concentration was elevated in a small stream passing through the farm and in the shallow aquifer beneath it. Needham Creek, the receiving water body for runoff and base flow from the farm watershed, had elevated salt concentrations when ponds were partially drained for harvest in the fall. At this time, chloride concentration exceeded 230 mg/L, the maximum concentration allowed by Alabama Department of Environmental Management regulations. Greater water reuse or more gradual release of pond effluent during harvest would reduce the peak in‐stream chloride concentration and avoid noncompliance with the in‐stream chloride criterion.     

Nursery rearing of the Asian catfish, Clarias macrocephalus (Günther), at different stocking densities in cages suspended in tanks and ponds

Growth and survival of hatchery‐bred Asian catfish, Clarias macrocephalus (Günther), fry reared at different stocking densities in net cages suspended in tanks and ponds were measured. The stocking densities used were 285, 571 and 1143 fry m^?3 in tanks and 114, 228 and 457 fry m^?3 in ponds. Fish were fed a formulated diet throughout the 28‐day rearing period. Generally, fish reared in cages in ponds grew faster, with a specific growth rate (SGR) range of 10.3–14.6% day^?1, than those in cages suspended in tanks (SGR range 9–11.3% day^?1). This could be attributed to the presence of natural zooplankton (copepods and cladocerans) in the pond throughout the culture period, which served as additional food sources for catfish juveniles. In both scenarios, the fish reared at lower densities had significantly higher SGR than fish reared at higher densities. In the pond, the SGR of fish held at 228 and 457 m^?3 were similar to each other but were significantly lower than those of fish held at 114 m^?3. The zooplankton in ponds consisted mostly of copepods and cladocerans, in contrast to tanks, in which rotifers were more predominant. Per cent survival ranged from 85% to 89% in tanks and from 78% to 87% in ponds and did not differ significantly among stocking densities and between rearing systems. In conclusion, catfish nursery in cages suspended in tanks and ponds is density dependent. Catfish fry reared at 285 m^?3 in tanks and at 114 m^?3 in ponds had significantly faster growth rates than fish reared at higher densities. However, the desired fingerling size of 3–4 cm total length for stocking in grow‐out culture can still be attained at stocking densities of 457 m^?3 in nursery pond and 571 m^?3 in tanks.     

Dry-Tilling of Pond Bottoms and Calcium Sulfate Treatment for Water Quality Improvement

Three different pond bottom treatments were evaluated in 12 earthen ponds. Bottoms of four ponds on the Auburn University Fisheries Research Unit, Auburn, Alabama, were dried for 1 mo and tilled with a roto-tiller (dry-till treatment). Four other ponds were dried and tilled, and after filling with water, enough gypsum (calcium sulfate) was applied to give a total hardness of about 200 mg/L. Gypsum was reapplied as needed to maintain the hardness (dry-till with gypsum treatment). Four ponds were not subjected to bottom drying, tilling or gypsum treatment (controls). Channel catfish Ictalurus punctatus fingerings were stocked at 15,000/ha. Selected water quality variables were measured at 1- to 2-wk intervals during the growing season. Concentrations of most variables increased over time because feeding rate was increased progressively as fish grew. Compared to the controls, both treatments had lower concentrations of total phosphorus and soluble reactive phosphorus, and higher concentrations of dissolved oxygen ( P < 0.05). In addition, ponds of the dry-till with gypsum treatment had in addition lower concentrations ( P < 0.05) of chlorophyll a , chemical oxygen demand, gross primary productivity, and total alkalinity than control ponds. The reduction in chlorophyll a concentration suggested less phytoplankton in gypsum-treated ponds, and this effect was probably related to lower phosphorus availability because of calcium phosphate formation. Secchi disk visibility, total suspended solids concentrations, and turbidity did not differ significantly among the treatments ( P < 0.05). Total fish production and survival rate did not differ significantly ( P < 0.05) among the treatments. These findings suggest that water quality improvement can be achieved by drying and tilling pond bottoms between crops, and benefits possibly may be increased by treating low hardness waters with gypsum.     

Biochemical Oxygen Demand in Channel Catfish Ictalurus punctatus Pond Waters

A study of the biochemical oxygen demand (BOD) of waters from ten channel catfish ponds at Auburn, Alabama, revealed that the 5-d BOD (BOD₅) seldom exceeded 8 mg/L and that the ultimate BOD (BOD_u) was usually less than 30 mg/L. Water samples from catfish ponds usually needed to be diluted only 2 or 3 times to permit BOD₅ measurements, and nitrification occurred even during a 5-d incubation period. Catfish pond waters were not extremely high in ammonia nitrogen concentration, and ammonia nitrogen introduced in the ammonium chloride-enriched dilution water caused an appreciable increase in BOD of some samples. Plankton respiration is a major component of carbonaceous BOD (CBOD) in catfish pond waters. Thus, the BOD is not expressed as rapidly during 5-d incubations as in typical waste-water. The ultimate BOD (BOD_u) would be a good measurement of oxygen demand for catfish pond effluents, but it is difficult to measure. Data from this study suggest that BOD_u can be estimated from BOD₅, but the correlation is not strong ( R ²= 0.62). An alternative is to develop a short-term BOD measurement specifically for effluents from channel catfish and other aquaculture ponds. This study suggests that a 10-d BOD conducted without nitrification inhibition or addition of ammonia nitrogen in dilution water might be a better alternative to standard BOD₅ or BOD_u measurements normally used in wastewater evaluation.     

Preliminary studies on rearing of the gilthead seabream, Sparus aurata (L.), in brackish water ponds

The first attempt to rear the gilthead seabream, Sparus aurata, in brackish water ponds in Egypt was conducted from April 1976 to February 1977. Experimental ponds were stocked with Sparus aurata fry of about 32 mm and 1.5 g average length and weight respectively at a rate of 3000 fry per one feddan of pond water (i.e. 0.42 ha). The growth rate was recorded monthly. An average length and weight of 190 mm and 78 g respectively was attained after 8 months without supplementary feeding or fertilization of pond water. mathematical equations expressing length-weight relationship and condition factor were derived for both wild and reared fish. The higher values of condition factor obtained for the reared fish in comparison to the wild fish signify their improved condition and hence their suitability for farming in Egypt.     

Farm-level costs of settling basins for treatment of effluents from levee-style catfish ponds

Compelled by pending regulatory rule changes, settling basins have been proposed as a treatment alternative for catfish pond effluents, but the associated costs to catfish farmers have not been estimated. Economic engineering techniques were used to design 160 scenarios as a basis for estimating total investment and total annual costs. For static-water, levee-style catfish pond facilities, sizing of settling basins is controlled by factors such as type of effluent to be treated, pond layout, size of the largest foodfish pond, number of drainage directions, scope of regulations governing effluents, and the availability of land. Regulations that require settling basins on catfish farms would increase total investment cost on catfish farms by $126–2990 ha⁻¹ and total annual per-ha costs by $19–367 ha⁻¹. More numerous drainage directions on farms resulted in the greatest increase in costs. While both investment and operating costs increased with larger sizes of foodfish ponds, costs per ha were relatively greater on smaller than on larger farms. For farms on which existing fish ponds would have to be converted to settling basins, over half of the cost was due to the production foregone and annual fixed costs of the pond. Requiring catfish farmers to construct settling basins would impose a disproportionately greater financial burden on smaller farms. The magnitude of the increased costs associated with settling basins was too high relative to market prices of catfish for this technology to be economically feasible.     

Threadfin Shad Dorosoma petenense Effects on Water Quality, Phytoplankton, and Channel Catfish Production in Ponds

Threadfin shad Dorosoma petenense are often stocked into commercial catfish ponds for biological control of algae. It is thought that the fish will alter the phytoplankton community, improve water quality, and enhance channel catfish production. Co-stocking of shad and catfish is a common practice, although there is limited information regarding the effects of threadfin shad on pond dynamics and catfish production. To evaluate the influence of shad in catfish ponds, this study was conducted in ten 0.04-ha experimental earthen ponds near Auburn, Alabama. All ponds were stocked in April with 600 fingerling channel catfish Ictal-urus punctatus (13,200/ha) with a mean length of 10.4 cm (4.1 in). Additionally, five of these ponds were randomly chosen and stocked with 70 adult threadfin shad (1,750/ha) weighing a total of 3.3 kg (16.5 kg/ha). At harvest in November, an average of 1,284 threadfin shad (32,100/ha), weighing a total of 55 kg (1,375 kg/ha) were collected from each shad pond. Water quality was improved with the addition of threadfin shad to channel catfish ponds. Mean total ammonia-nitrogen was significantly lower and less variable in the shad treatment. Observed mean nitrite concentrations, though not significant, were lower in the shad treatment. The phytoplankton community of the shad treatment had significantly higher density, more taxa, and smaller organisms. Pond water in the shad treatment had higher projected early morning dissolved oxygen levels requiring less aeration. Channel catfish had significantly higher survival in the shad treatment, furthermore, though not statistically significant, observed mean fish production was higher and feed conversion ratio was lower than in the no-shad treatment.     

Effect of Dietary Protein Concentration and Stocking Density on Production Characteristics of Pond-Raised Channel Catfish Ictalurus punctatus

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.     

Characteristics of Effluents from Central Arkansas Baitfish Ponds

Scientific information on baitfish effluents is important to provide a basis for the development of appropriate and cost-effective management practices that minimize environmental impacts. Effluents from 10 commercial golden shiner Notemigonus crysoleucas ponds in central Arkansas were sampled December 2000 through June 2001. Grab samples of the first and last 10% of pond volume were collected during intentional draining events. Effluents were sampled as they exited pond drainpipes and at the ends of drainage ditches just prior to stream discharge. Concurrent receiving stream samples were collected upstream and downstream of the discharge point. Total nitrogen (TN), total phosphorus (TP), 5-d biochemical oxygen demand (BOD_S), and total suspended solids (TSS) of each sample were measured. Mean whole effluent concentrations for the first 10% were 36 mg TSS/L, 9 mg/L BOD₅, 2 mg TN/L, and 0.5 mg TP/L. The water quality of the first and last 10% of pond effluent were not significantly different ( P < 0.05). Filtering effluents through a 5-pm mesh screen did not significantly reduce nutrient concentrations. Serial fractionation of effluents resulted in small but significant decreases in TSS concentrations in samples filtered through the 10, 8, and 5-μm meshes ( P < 0.05). Effluent discharge through farm ditches generally did not improve effluent water quality. Effluents collected at ditch ends were significantly less than drainpipe samples in BOD, concentrations only ( P < 0.05). Limited data on receiving stream water quality indicated that only TP concentrations were greater in pond effluents than in receiving streams. Overall, baitfish pond effluents are similar in composition to effluents of other phytoplankton-based pond production systems.     

Delayed Feeding of Channel Catfish Fry Stocked in Ponds

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.     

Estimates of Bottom Soil and Effluent Load of Phosphorus at a Semi-intensive Marine Shrimp Farm

A phosphorus budget for a single crop was prepared for a 685‐ha semi‐intensive shrimp farm that consistently has produced about 3000 tonnes/yr of black tiger prawn, Penaeus monodon. Phosphorus inputs were shrimp stock, 0.31 kg/ha; triple superphosphate, 1.38 kg/ha; incoming water, 25.8 kg/ha; and feed, 65.3 kg/ha. Phosphorus outputs were harvested shrimp, 5.43 kg/ha, and outflow for water exchange and draining, 42.7 kg/ha. The high clay‐content soil in pond bottoms adsorbed 45.2 kg/ha of phosphorus. Water was taken from and released back into the same estuary and bay. The phosphorus contribution of shrimp farming to the receiving water body was the difference between the amount of phosphorus in effluent and that in the incoming water, which was 16.9 kg/ha. Bottom soil accumulated 67.8% of phosphorus added to the ponds. Another estimate of soil phosphorus uptake based on the relationship between cumulative phosphorus applied to ponds as fertilizer and feed and soil phosphorus concentration suggested that 63.2% of fertilizer and feed phosphorus had accumulated in pond bottoms. The farm effluent phosphorus load was 23.5 tonnes/yr. The estuary and bay system has an estimated volume of 4.8 × 10⁹ m³, and the annual phosphorus input from the farm had a concentration equivalent of 0.005 mg/L, and there were no other major inputs of phosphorus. The estuary and bay are flushed by freshwater inflow and tidal action, and the farm input is not likely to cause eutrophication.     

Water use and conservation for inland aquaculture ponds

The general hydrological equation, inflow = outflow ± change in storage, can be used to make accurate estimates of water use by ponds for inland aquaculture projects. The primary inflows are precipitation, runoff and regulated water additions. The main outflows are evaporation, seepage, overflow after storms and intentional discharge. Water conservation measures such as maintaining storage capacity in ponds equal to the normal, maximum daily precipitation, reduction in seepage beneath dams and through pond bottoms, fish harvest without draining ponds, and water re-use are discussed. Even with the implementation of water conservation measures, pond aquaculture is a water- intensive endeavour which consumes more water per unit of area than irrigated agriculture. However, the value of aquacultural production per unit of water used greatly exceeds that of irrigated agriculture. Reduction in effluent volume is the most effective water saving means, and not only reduces water consumption but also reduces the pollution potential of pond aquaculture.     

Effects of a Bacterial Inoculum in Channel Catfish Ponds

A commercial bacterial Inoculum cultured on site called Biostart was applied to three channel catfish Ictalurus punctatus ponds at Auburn, Alabama, USA, three times per week from May until October 1996. There were few significant differences (P × 0.1) in concentrations of water quality variables between ponds treated with bacteria and control ponds. In addition, bottom soil carbon and nitrogen did not differ between treated and control ponds. However, survival and net production of fish was significantly (P × 0.1) greater in ponds that received the bacterial inoculum than in controls. The mechanism by which the bacterial treatment influenced fish survival cannot be explained from data collected in this study. Further studies of probiotics are needed to define the potential benefits of these treatments to aquacultural production and to determine their mechanisms of action in pond ecosystems.     

Impact of Copper Sulfate on Plankton in Channel Catfish Nursery Ponds

Many fish culturists are interested in applying copper sulfate pentahydrate (CSP) to channel catfish, Ictalurus punctatus, nursery ponds as a prophylactic treatment for trematode infection and proliferative gill disease by killing snails and Dero sp., respectively, before stocking fry. However, copper is an algaecide and may adversely affect phytoplankton and zooplankton populations. We evaluated the effects of prophylactic use of copper sulfate in catfish nursery ponds on water quality and phytoplankton and zooplankton populations. In 2006, treatments of 0 mg/L CSP, 3 mg/L CSP (0.77 mg/L Cu), and 6 mg/L CSP (1.54 mg/L Cu) were randomly assigned to 0.04‐ha ponds. In 2007, only treatments of 0 and 3 mg/L CSP were randomly assigned to the 16 ponds. Ponds treated with CSP had significantly higher pH and significantly lower total ammonia concentrations. Treatment of both CSP rates increased total algal concentrations but reduced desirable zooplankton groups for catfish culture. CSP has been shown to be effective in reducing snail populations at the rate used in this study. CSP treatment also appears to be beneficial to the algal bloom, shifting the algal population to green algae and increasing total algal biomass within 1 wk after CSP treatment. Although zooplankton populations were adversely affected, populations of important zooplankton to catfish fry began rebounding 6–12 d after CSP treatment. Therefore, if CSP is used to treat catfish fry ponds of similar water composition used in this study, fry should not be stocked for about 2 wk after CSP application to allow time for the desirable zooplankton densities to begin increasing.     

Possible Effects of Sodium Chloride Treatment on Quality of Effluents from Alabama Channel Catfish Ponds

Channel catfish ponds are treated with salt (sodium chloride) to increase chloride concentration and prevent nitrite toxicity in fish. A survey indicated that most farmers try to maintain chloride concentration of 50 to 100 mg/L in ponds by annual salt applications. Averages and standard deviations for selected water quality variables in salt-treated ponds were as follows: chloride. 87.2 ± 37.5 mg/L; total dissolved solids (TDS), 336 ± 96 mg/L; specific conductance, 512 ± 164 μmhos/cm. Maximum values were 189 mg/L for chloride, 481 mg/L for TDS, and 825 μmhos/cm for specific conductance. Good correlations between specific conductance values and both chloride and TDS concentrations suggest that specific conductance can be a rapid method for estimating concentrations of these two variables in surface water. The maximum limit for chloride concentration in Alabama streams allowed by the Alabama Department of Environmental Management is 230 mg/L. The usual recommended upper limit of TDS for protection of aquatic life in freshwater streams is 1,000 mg/L. Based on the observed relationship between TDS concentration and specific conductance in Alabama catfish ponds, 1,000 mg/L TDS corresponds to 1,733 μmhos/cm specific conductance. It is unlikely that effluents from salttreated catfish ponds would violate the in-stream chloride standard of 230 mg/L or harm aquatic life in streanis. Nevertheless, chloride concentrations in ponds should be measured before salt application as a safe guard against excessive salt application and chloride concentrations above the in-stream chloride standard.     

Fish polyculture system integrated with vegetable farming improves yield and economic benefits of small‐scale farmers

This study explored the yield and economic benefits of African sharptooth catfish, Clarias gariepinus, and Nile tilapia, Oreochromis niloticus polyculture, reared in earthen ponds for 270 days integrated with Chinese cabbage, Brassica rapa chinensis, farmed for 45 days to small‐scale farmers in Tanzania. An integrated aquaculture–agriculture (IAA) system involving fishes and vegetables resulted in three and 2.5 times higher net yield than the culture of fishes alone and farming of non‐integrated vegetables respectively. Vegetables irrigated with pond water resulted in 1.8 times higher net and annual yields than those irrigated with stream water. The practice of fish–vegetable integration and growing of vegetables irrigated with pond water produced 14 and 13 times higher net annual yield, respectively, than the culture of fishes alone. The integrated system produced 20 and 150 times more net returns compared with vegetables irrigated with pond and stream water respectively. Integrating fishes with vegetables resulted in significantly higher annual net cash flow than the farming of fishes and vegetables separately. The study revealed that integrating fishes with B. rapa chinensis increases yields, income and food production to small‐scale farmers. Thus, small‐scale farmers can adopt IAA technology to meet the increasing demand of fish and vegetables, stabilize their incomes and diversify food production, consequently improving food security. These benefits will be realized by providing proper training in IAA technology and management skills to small‐scale farmers.     

Overwintering performance of Nile tilapia Oreochromis niloticus (L.) broodfish and seed at ambient temperatures in northern Vietnam

Two experiments (E1 and E2) to assess the performance of tilapia broodstock and tilapia sex‐reversed fry in overwintering were conducted at the Research Institute for Aquaculture No.1 (RIA‐1) in the cold seasons of 1995–96 and 1996–97. Nile tilapia Oreochromis niloticus (L.) broodstock of the Thai, GIFT, Egypt and Viet strains were overwintered in deep and shallow ponds, as well as in deep and shallow hapas suspended in a single deep pond for evaluation of the influence of overwintering systems on the survival and growth of fish. Large (> 1 g) and small (< 1 g) tilapia seed were overwintered in deep hapas‐in‐ponds for comparison of their performance. In 1995–96, the coldest pond water temperature was 10–11 °C, and survival of tilapia broodfish overwintered in deep and shallow hapas‐in‐ponds was 99.6–100%. This was significantly (P < 0.05) higher than fish stocked in deep and shallow ponds (74.4–90%). The survival rate of larger monosex tilapia fry was 54%, which was significantly (P < 0.05) higher than that of smaller fry (33.4%). In 1996–97, the lowest pond water temperature was 15.8 °C, and fry showed similarly high survival rates in all treatments (97–100%). There was no significant difference between fry in the two size classes. The results of this study clearly indicate that hapas‐in‐ponds are useful for reducing the risk and improving the survival of tilapia broodstock and fry in the cold season. Differences in the decline in ambient temperatures year on year mean that the need for special overwintering conditions varies. Hapas‐in‐ponds are a low‐cost overwintering method that can be one of the appropriate strategies for tilapia seed production under the variable, cool temperature regimes in northern Vietnam.     

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.     

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.