The impact of a commercial microbial population (product name “RAS Right”) on the off-flavours geosmin and 2-methylisoborneol (2-MIB) in water and fish of a recirculating aquaculture system (RAS) for Nile tilapia production was studied over five months. The “RAS Right” product contains a microbiome that is reported to reduce geosmin. In the system that received “RAS Right”, geosmin ranged from 1.6 to 171.2 ng/L, while 2.4 to 89.3 ng/L occurred in the control RAS. After fluctuations in the first two months, water in the control RAS had lower geosmin concentrations (mean of 8.8 ng/L) than the treated RAS (mean of 16.6 ng/L). 2-MIB was low (<4.3 ng/L) or undetectable in both the control and treated systems. In the fish, geosmin varied from 112 to 3683 ng/kg, with the highest levels measured in the treated RAS during three of eight samplings. 2-MIB in the fish ranged from 11.6 to 136 ng/kg and peaked in the treated RAS in one sampling. The results indicate that “RAS Right” did not produce a significant reduction of geosmin or 2-MIB in water or fish. However, optimisation of the treatment with respect to dose or addition frequency may improve its effect, though this remains to be examined.
Noguera et al. (Tue,) studied this question.