Off-flavors in pond-grown ictalurid catfish: Causes and management options

Ictalurid catfish grown in ponds often acquire undesirable off-flavors prior to harvest. Off-flavors develop when odorous, lipophilic substances in food or water are absorbed across gut or gill epithelium and concentrated in edible tissues. The most common causes of catfish off-flavors are two nontoxic secondary metabolites of planktonic cyanobacteria: geosmin (causing an earthy off-flavor) and 2-methylisoborneol (causing a musty off-flavor). Off-flavored fish are unacceptable for processing, and harvest must be postponed until the source of the odorous compound disappears and the compound purges from edible fish tissue. Harvest delays caused by episodes of off-flavor increase production time, interrupt cash flow, and increase the risk of fish loss. Catfish farmers consider off-flavor to be one of their most important production-related problems. This paper reviews the causes of off-flavor in catfish, pharmacokinetics of uptake and loss of odorous compounds in catfish, seasonality and prevalence of off-flavors, farm- and industry-level impacts, the ecology of cyanobacteria in catfish ponds, and various strategies for preventing or treating cyanobacterial (and other) off-flavors. A decision-making system based on knowledge gained from research is presented as a guide to effective use of the limited tools available to manage off-flavors.