Management of musty off-flavor in channel catfish from commercial ponds with weekly applications of copper sulfate

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 degrees 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 significantly lower in treated ponds than in control ponds at one farm, while numbers of green algae and diatoms at both farms were significantly higher in treated ponds than in control ponds. Also, fish flavor analysis indicated that the overall prevalence of all types of off-flavor was 50% lower in treated ponds than in control ponds. Based upon our results, weekly low-dose applications of copper sulfate appear to be beneficial in mitigating musty off-flavor problems in commercially produced channel catfish. Copper sulfate treatment reduced potential harvest delays by nearly half and reduced costs associated with off-flavor by 35%. However, the economic benefit of treatment was not statistically significant, although this result is probably attributable to the small data set used for economic analyses rather than ineffectiveness of treatment.