The ratio between digestible protein and digestible energy affects accumulation and depuration of geosmin and 2‐methylisoborneol (2‐MIB) in Japanese seabass ( Lateolabrax japonicus ) raised in a recirculated aquaculture system

Actinobacteria and cyanobacteria accounted for less than 1% of total of bacteria in water in a recirculated aquaculture system (RAS) during a 15-week feeding trial with 0.11-g Japanese seabass. Resulting concentration of geosmin and 2-methylisoborneol (2-MIB) in RAS water was 169 and 45 ng L−1, sufficient to produce strong off-flavour. The seabass were fed diets with 42%, 45% and 49% protein, and each protein level was supplemented with 15% or 18% lipid. Accumulation of off-flavours was independent of diet in fatty ventral tissue. Dietary protein significantly reduced off-flavours in lean, dorsal tissue. This was mainly rationalized by linear reduction in 2-MIB in response to increasing DP/DE and a strong, 2nd degree polynomial response in geosmin. The ratio between geosmin and 2-MIB was slightly higher at the beginning of a 10-day period with clean water and fasting, than what was observed throughout depuration. 2-MIB remained between 0.2 and 1 µg kg−1 in dorsal tissue throughout depuration. Geosmin in ventral tissue ranged from 10 to more than 30 µg kg−1at the termination of the feeding period and was reduced to a range from 6 to 20 µg kg−1 by depuration.