The recovery of flavor quality by channel catfish

Intensive production of channel catfish Ictalurus punctatus requires copiou s feeding. Nutrients from uneaten feeds and fish excreta contribute to the growth of microorganisms. Certain microbes that occur frequently in aquacul ture systems produce the "muddy and earthy" off-flavor metabolites 2w-methy lisoborneol (MIB) and geosmin. Fish containing MIB or geosmin can exhibit a n off-flavor that makes them unacceptable for harvest as food fish. Followi ng the cessation of exposure to MIB or geosmin, fish depurate off-flavors. The minimum period required for fish to regain flavor quality is a critical concern for aquaculturists; scant information concerning this period promp ted our investigation. Channel catfish were harvested from three commercial ponds, and fish from each pond were sorted into four size-classes (0.4-0.8 kg, 0.8-1.3 kg, 1.3-1.6 kg, and 1.6-2.3 kg) on 30 August (summer) and on 1 8 October (autumn) 1993. Each group of fish was transferred into individual 2,000-L fiberglass tanks, and each tank was supplied with groundwater (14 L/min). Geosmin was observed at the fall harvest only. Periods required for the mean MIB concentration of each group of fish to reach an estimated acc eptance threshold of 0.7 mu g/L were similar at both harvests and ranged fr om about 96 to 150 h. Periods required for a population of fish to recover flavor quality (defined as the point when more than 80% of the fish had MIB concentrations below the level that would cause rejection as food fish) we re greater than periods required for the mean MIB concentration to reach 0. 7 mu g/L and ranged from 150 to 500 h.