Interactive effects of temperature and water exchange of depuration tanks on geosmin excretion by Atlantic salmon (Salmo salar)

Fish farmers utilize the reversibility of the bioconcentration process to depurate geosmin and other off- flavour causing chemicals from their fish by placing them in clean water just before harvest. To better understand and improve this process, we investigated effects of temperature and water exchange of depuration tanks on geosmin elimination from Atlantic salmon (Salmo salar). Fish loaded with geosmin were depurated for 144 h during which they were subjected to combinations of water exchange (stagnant water or a water exchange rate of ~1200 L/kg fish/d) and temperature (~11.5 or ~14.5 °C) treatments. Model predictions indicated enhanced depuration by water exchange, elevated temperature and interactive effects of these two factors, plus geosmin accumulation in the depuration tank water. The latter was predicted but not observed in the experiment. Furthermore the elevated temperature did not enhance geosmin elimination from Atlantic salmon, possibly because in the tanks with water exchange, temperature treatments did not cause differences in oxygen levels and thus gill ventilation rates. The water exchange significantly increased geosmin elimination from Atlantic salmon, indicating that removal of excreted geosmin from the direct environment of this fish is needed to obtain maximal geosmin elimination from the fish.