Physiology Approaches to the Management of Off-Flavors in Farm-Raised Channel Catfish,Ictalurus punctatus

Abstract

To obtain optimal yields of channel catfish, Ictalurus punctatus, large quantities of feed are added to ponds. Nutrients released from feed support dense algal and bacterial populations. Although some microbes produce oxygen and remove wastes, certain taxa produce the muddy/earthy off-flavor metabolites, 2-methylisoborneol (1-R-exo-1, 2, 7, 7-tetramethyl-bicyclo-[2, 2, 1]-heptan-2-ol) (MIB) and geosmin (1α, 10β-dimethyl-9α-decalol). Currently, off-flavors are one of the biggest problems affecting the channel catfish industry. Fish exposed to water containing either geosmin or MIB rapidly concentrations of these compounds in their tissues. Conversely, fish placed in water free of off-flavor metabolites exhibited markedly reduced concentrations of MIB after 8 hours and continued to improve in flavor quality throughout 24 hours, indicating a progressive purging or clearing of off-flavor compounds from their tissues. Relatively lean (< 2.5% fat) fish lost MIB more rapidly than fish with greater fat contents (> 2.5% fat). This paper proposes that aquaculture production systems should be managed for maximum production efficiency and yields, and that fish containing off-flavors then could be purged in special facilities. Purging systems that rely on a constant flow require large amounts of water and may not be widely practical. Systems that recirculate water may be more feasible. However, biological filters and other components of recirculating systems may become sources of off-flavors. The early detection of off-flavor-producing taxa and the competitive exclusion of problematic populations may be useful in preventing off-flavor production in recirculating purging systems.