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-yea r study to evaluate the effect of weekly copper sulfate applications on the incidence and economic impact uf environment-induced off-flavors in channe l catfish Ictalurus punctatus. Each spring, when water temperatures increas ed above 20 degreesC. nine ponds were treated weekly with 0.12 mg Cu/L. Tre atments were discontinued each fall when water temperatures fell below 20 d egreesC. Overall prevalence of off-flavor was reduced by 80% for ponds trea ted with copper sulfate compared with control ponds, and episodes of off-fl avor were of shorter duration in treated ponds. Off-flavors never delayed f ish 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 d ue 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 t reated with copper sulfate. Variation in net returns was twice as great for control ponds as for treated ponds, indicating increased stability in prod uction and economic returns when off-flavors were managed with the use of c opper sulfate. High variation in annual economic performance on control pon ds resulted from one or more ponds having high net returns while one or mor e ponds had extremely poor returns due to protracted episodes of off-flavor .