RELATIONSHIP BETWEEN WATER-QUALITY, PHYTOPLANKTON COMMUNITY AND OFF-FLAVORS IN CHANNEL CATFISH (ICTALURUS-PUNCTATUS) PRODUCTION PONDS

Off-flavor in the flesh of channel catfish (Ictalurus punctatus) and in the pond water was studied under two recirculation regimens in twelve 0.04-ha ponds stocked with 15 000 fingerling channel catfish/ha. Water was recirculated through a biological filler by centrifugal pumping for 24 h in six ponds and for 12 h in the other six ponds. In each pond, food quality, phytoplankton populations, and geosmin and 2-methylisoborneol (MIB) concentrations were evaluated weekly during the last 8 weeks of the growing season (mid September to early November). Food quality was determined from average taste panel scores for earthy-musty flavors. Objectionable off-flavor was detected by the trained panel in 13.5% of the 96 sample units (ponds X weeks). Levels of geosmin and MIB in the water ranged from 0.000 to 0.097 mug/l for geosmin (excepting one measurement of 0.649 mug/1), and 0.039 to 0.356 mug/l for MIB. Off-flavor scores and concentrations of geosmin and MIB in the water did not significantly differ between the two pond recirculation treatments. Objectionable off-flavor scores (> 1.0) were significantly correlated (P < 0.05) with the prior week's MIB values and degree of Oscillatoria domination. MIB levels and Oscillatoria dynamics leading to dominance conditions were indicative of off-flavor problems in subsequent weeks and may be used in a-predictive manner.