Experimental validation of a time-dependent model for chemical taste taint accumulation as geosmin (GSM) and 2-methylisoborneol (MIB) in commercial RAS farmed barramundi (Lates calcarifer)

The accumulation of naturally-derived taste taint chemicals, geosmin (GSM) and 2-methylisoborneol (MIB), impair the flavour of Recirculating Aquaculture System (RAS) farmed-fish. Quantification and control of these by analytical or sensory means are not presently practical for RAS farmers. To forecast taste taint in RAS, a time-dependent model was synthesised (Ecological Modelling 291 (2014) 242-249). Here we report for the first time an extensive two-year validation study of this model with commercial RAS farmed barramundi (Lates calcarifer) in which fingerlings (∼0.01 kg) were grown to harvest (∼0.85 kg) at 245 days. The concentration of GSM and MIB in the growth water and fish-flesh was determined (weekly) using Headspace Solid-Phase Micro-Extraction, followed by Gas Chromatography Mass-Spectroscopy (and microwave-mediated distillation). The concentration of both taint chemicals in the RAS growth water was controlled using continuous dosing of hydrogen peroxide (2.5 mg L−1) as a benign biocide. A special dosing apparatus was developed for this purpose. Results showed, generally, very good agreement between observed and predicted taint values in the range 0-2 μg kg−1, and especially below the important consumer rejection threshold (<∼0.7 μg kg−1). A minor anomaly was a general over-prediction of chemical in about a half of the N = 706 simulations in the range 0-12 μg kg−1. Predictions were conservative therefore i.e. on the 'safe' side. This is attributed, largely, to dissimilar (exponential) growth constant (γ) for smaller and larger fish, and the fact that the RAS environment is oscillatory. Findings highlight that the work could be meaningfully applied to RAS systems to develop protocols to limit taste taint in harvested fish. Significantly, these results are the first for RAS farmed-fish covering an entire production cycle from fingerlings to harvest. The work will be of immediate benefit and interest to RAS farmers, selling agents and researchers.