Effect of feeding during off-flavour depuration on geosmin excretion by Nile tilapia (Oreochromis niloticus)

The effect of feeding during off-flavour depuration on the elimination of geosmin from muscle tissue (fillet) and ovaries as a model for caviar was assessed in Nile tilapia (Oreochromis niloticus) (mean ± SD weight of 185 ± 15.0 g). The experiment had a 2 × 4 factorial design with feeding level (starved or fed) and depuration time (24, 48, 72 and 96 h) as factors with duplicates for each of the 8 treatment combinations. Fish were normally loaded with geosmin prior to the experiment. During off-flavour depuration geosmin levels in fillet and ovary declined over time in both fed and starved tilapia. In fed tilapia geosmin declined faster from the ovaries compared to starved fish (p = 0.018). The same trend of a faster decline was observed for the muscle tissue (fillets) of fed tilapia, though only numerically (p = 0.11). Because faster geosmin elimination paralleled with high blood lipids, we do not rule out that blood lipids are involved in geosmin transport via the circulatory system and that low blood lipid levels are limiting geosmin elimination in starved fish. No difference in geosmin elimination rate was detected between ovary and muscle tissue in Nile tilapia. Off-flavour depuration time is strongly reduced when farmers adopt a practice of feeding Nile tilapia during off-flavour depuration.