Management of off-flavors in pond-cultured channel catfish with weekly applications of copper sulfate

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 uf environment-induced off-flavors in channel catfish Ictalurus punctatus. Each spring, when water temperatures increased above 20 degreesC. nine ponds were treated weekly with 0.12 mg Cu/L. Treatments were discontinued each fall when water temperatures fell below 20 degreesC. 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 where harvest was delayed due to off-flavor. Enterprise budgets showed that average net returns above variable costs were US$1,900/ha for control ponds and $2,720/ha for ponds treated with copper sulfate. Variation in net returns was twice as great for control ponds as for treated ponds, indicating increased stability in production and economic returns when off-flavors were managed with the use of copper sulfate. High variation in annual economic performance on control ponds resulted from one or more ponds having high net returns while one or more ponds had extremely poor returns due to protracted episodes of off-flavor.