Effects of exercise and temperature on geosmin excretion by European eel (Anguilla anguilla)
The presence of geosmin in fish products causes an earthy or musty off-flavour. To avoid economic damage resulting from market entrance of off-flavoured fish products, fish farmers utilize the reversibility of geosmin uptake to depurate the off-flavours from their fish crops by holding them in clean water just before harvest. To improve this process, effects of exercise and temperature on the excretion of geosmin by European eel (Anguilla anguilla) were assessed. Fish loaded with geosmin were depurated for 23 h during which they were subjected to combinations of exercise (spontaneous swimming activity at 0.05 m s− 1 or forced swimming at optimal swimming speed of 0.55 m s− 1) and temperature (15 °C or 25 °C) treatments. Oxygen consumption was measured during depuration. Whole body geosmin concentrations were measured in samples collected at t = 0 and t = 23 h to assess geosmin excretion. Geosmin excretion by European eel was clearly enhanced by exercise, but temperature had no statistically significant effect. Exercise increased oxygen consumption, which in turn showed a positive linear relation with geosmin excretion. These findings support the idea that the physiological responses aimed at increasing oxygen uptake also affect the branchial exchange of lipophilic xenobiotic chemicals between the fish and its surroundings. Exercise can be used to reduce the time required to depurate off-flavours from fish. These findings are relevant for aquaculture industries confronted with off-flavoured fish crops.
Statement of relevance
Fish raised in land-based aquaculture systems may bio-concentrate geosmin, a lipophilic organic compound produced by microbiota. The presence of geosmin in fish products causes an earthy or musty off-flavour which human consumers do not appreciate and this poses one of the most significant economic problems for land-based aquaculture. To avoid economic damage resulting from market entrance of off-flavoured fish, fish farmers utilize the reversibility of geosmin bio-concentration to depurate the off-flavours from their fish crops. To this end fish are kept in water free of geosmin just before harvest. This procedure, however, is not always sufficiently effective and it is costly as it requires time, effort and use of specific facilities. Therefore better understanding of factors enhancing the geosmin excretion is needed to be able to improve the off-flavour depuration process. This study established that forced exercise during off-flavour depuration increases the rate at which European eel eliminates geosmin from its body. Forcing fish to swim during off-flavour depuration shortens the required depuration time. This finding is relevant for the aquaculture industries confronted with off-flavoured fish crops.