Susan K. Kingsbury

Effects of water management practices on discharge of nutrients and organic matter from channel catfish (Ictalurus punctatus) ponds

Abstract A water quality data set generated by sampling commercial ponds for 2 years was used in a hydrological model of pond overflow volume to describe the effects of water management practices on discharge of nutrients and organic matter from channel catfish Ictalurus punctatus ponds in northwest Mississippi, USA. Average concentrations of total nitrogen, total phosphorus, chemical oxygen demand, and biochemical oxygen demand in pond waters were highest in the summer but waste discharge was strongly influenced by pond overflow volume, and the model indicated that greatest quantities of nutrients and organic matter were discharged in the winter when pond overflow volume was greatest. The model also showed that managing pond water levels to maintain a minimum 7.5-cm water storage potential reduced average discharge of nitrogen, phosphorus, and organic matter in pond overflow by about 70% compared with ponds not managed to maintain storage potential. The model further showed that harvesting fish without draining ponds between fish crops could reduce average annual nutrient and organic matter discharge by over 60% relative to annually drained ponds. Maintaining water storage potential and not draining ponds between fish crops therefore appear to be simple and effective methods of reducing waste discharge from aquaculture ponds and have the added benefit of substantially reducing the need for pumped water to maintain pond water levels.

Management of Off-Flavors in Pond-Cultured Channel Catfish with Weekly Applications of Copper Sulfate

Abstract Eighteen 0.4-ha earthen ponds in northwest Mississippi were used in a 3-year study to evaluate the effect of weekly copper sulfate applications on the incidence and economic impact of environment-induced off-flavors in channel catfish Ictalurus punctatus. Each spring, when water temperatures increased above 20°C, nine ponds were treated weekly with 0.12 mg Cu/L. Treatments were discontinued each fall when water temperatures fell below 20°C. Overall prevalence of off-flavor was reduced by 80% for ponds treated with copper sulfate compared with control ponds, and episodes of off-flavor were of shorter duration in treated ponds. Off-flavors never delayed fish harvest from treated ponds, whereas off-flavors delayed fish harvest on 10 occasions in control ponds. Average annual fish harvest was 5,900 kg/ha from ponds treated with copper sulfate and 5,349 kg/ha from control ponds. The 9% reduction in fish harvest from control ponds was due to infectious disease outbreaks in one or two ponds each year wh...

Evaluation of Ferulic Acid for Controlling the Musty-Odor Cyanobacterium, Oscillatoria perornata, in Aquaculture Ponds

Abstract The cyanobacterium Oscillatoria perornata f. attenuata, a common inhabitant of channel catfish, Ictalurus punctatus, aquaculture ponds, produces the musty compound 2-methylisoborneol that causes fish to become off-flavor and unmarketable. Previous laboratory studies suggest that the natural compound trans-ferulic acid (4-hy-droxy-3-methoxycinnamic acid) is selectively toxic against O. perorna-ta. The present study was conducted to determine the effectiveness of the compound for controlling the growth of O. perornata under field conditions. The study was conducted in 12 0.1-ha earthern ponds in northwest Mississippi. Ponds contained 20,000 catfish/ha and were managed according to commercial culture practices. Half of the ponds were treated six times over a 2-month period with 5μM (0.97 mg/L) trans-ferulic acid, and the other half were untreated controls. Water samples obtained from all ponds preceding and following treatment were analyzed for phytoplankton community structure and concentrations of chlorophyll a, ferulate, and 2-methylisoborneol. Abundance of cyanobacteria, including O. perornata was not consistently affected by applications of ferulic acid. Only one of the six ferulic acid applications resulted in a decrease in abundance of O. perornata in treated ponds relative to untreated ponds (P <0.1). The ineffectiveness of trans-ferulic acid as a cyanobacterial algicide in catfish ponds appears to be caused by rapid dissipation of ferulic acid from pond waters. Use of trans-ferulic acid was neither an effective nor an economical approach to preventing musty off-flavor in pond-cultured channel catfish.

Management of Musty Off-Flavor in Channel Catfish from Commercial Ponds with Weekly Applications of Copper Sulfate

Abstract We evaluated the effectiveness of weekly low-dose applications of copper sulfate (0.12 mg of Cu/L of water) for reducing the prevalence of off-flavor in channel catfish Ictalurus punctatus on commercial farms. The study was conducted over 3 years in ponds (3.2–8.4 ha) on two catfish farms in western Mississippi. Farm managers applied copper sulfate (0.5 mg of copper sulfate pentahydrate/L of water) weekly beginning in the late spring or early summer and continued until the water temperature dropped below 20°C. Water samples were collected from treated and untreated ponds approximately every 3 weeks during the application period and were monitored for levels of the musty compound 2-methylisoborneol (MIB), chlorophyll a, and phytoplankton community structure and abundance. In addition, channel catfish were caught from each study pond during the third year of the study and were checked for flavor. Levels of MIB and the abundance of the MIB-producing cyanobacterium Oscillatoria perornata were signifi...

Bacterial Bioaugmentation of Channel Catfish Ponds

Abstract Twelve, 0.1-ha earthen ponds at Stoneville, Mississippi were used in a 2-year, double-blind study of the effects of a Bacillus-based bacterial bioaugmentation product on water quality and production of channel catfish Ictalurus punctatus. Each year, six ponds were treated weekly with the microbial product from late May or early June through October, and six ponds were designated as untreated controls. Mean concentrations of chlorophyll a, nitrite-N, and total ammonia-N did not significantly differ (P > 0.05) between bacteria-treated and untreated ponds in the first year; however, in the second year, mean chlorophyll-a concentrations were higher (P ≤ 0.05) and nitrite-N and total ammonia-N concentrations were lower (P ≤ 0.05) in bacteria-treated ponds than in untreated ponds. Reductions in dissolved inorganic nitrogen concentrations were more likely due to increased phytoplankton growth (i.e., increased algal assimilation) than to a direct effect of bacterial inoculation. The mechanism by which bi...

Dietary Phosphorus Modifications in Practical Feeds Do Not Affect Waterborne Phosphorus Concentrations and Phytoplankton Abundance in Channel Catfish Ponds

Abstract We measured concentrations of soluble reactive phosphorus, total phosphorus, and chlorophyll a in 0.04-ha ponds containing channel catfish Ictalurus punctatus during three feeding trials to evaluate the effect of dietary phosphorus modifications on water quality and the potential discharge of phosphorus and organic matter in pond effluents. In experiment 1, a basal diet with 0.20% available phosphorus was compared with diets supplemented with 0.5% or 1.0% dicalcium phosphate to provide 0.27% or 0.35% available phosphorus. In experiment 2, fish were fed diets supplemented with either dicalcium phosphate or defluorinated rock phosphate to contain 0.40% available phosphorus. In experiment 3, fish were fed one of three diets containing 250 or 500 phytase units of phytase per kilogram (0.27% available phosphorus) or 0.75% dicalcium phosphate (0.39% available phosphorus). Husbandry practices in all three experiments were typical of commercial culture conditions. Quantitative and qualitative modificatio...