44 Priyantha I. Hathurusingha and Kenneth R. Davey
and; a critical review of an extensive recent experimental validation of
one predictive model and risk analyses.Keywords: geosmin (GSM), 2 - methylisoborneol (MIB), Recirculating
Aquaculture Systems (RAS), predictive models, taste-taint
INTRODUCTION
Fish farmed in Recirculating Aquaculture Systems (RAS) is a globally
important alternative to capture of wild-fish, particularly as wild-caught
seafood population levels plateau or decline. RAS is increasingly important in
filling the demand gap and is becoming popular due to a higher production per
unit area, less water and land usage, a year-round production and better control
of the fish-rearing environment than other conventional fish farming methods
such as ponds and sea-cages (Ebeling and Timmons, 2012). Aquaculture such
as RAS is expected to grow and develop as the global demand for farmed
species grows.
A problem however is the potential for accumulation in the RAS growth
water, and consequently in the fish-flesh, of unwanted taste-taint as ‘off-
flavours’ and unpleasant odours. It has become a major concern in RAS
industry. Of particular interest are the taint-taste chemcials geosmin (GSM)
and 2-methylisoborneol (MIB).
The dynamics of the RAS growth water and taint environment are
complex, with the quantity of GSM/MIB in the growth water and fish-flesh
varying with micro-organism, system location, water nutrient(s), and fish
species and size (Howgate, 2004; Percival et al., 2008). A substantial number
of benthic cyanobacteria and actinomycetes species in aquaculture systems are
reported to produce taste-tainting chemicals (Izaguirre and Taylor, 2004).
Notably, cyanobacteria are thought to be the main micro-organism responsible
in conventional outdoor ponds, whereas actinomycetes are assumed to be the
associated micro-organism in RAS (Tucker, 2000; Howgate, 2004; Guttman
and van Rijn, 2008). In addition, there are several species of fungi and amoeba
that are also capable of producing these chemicals (Juttner and Watson, 2007;
Zaitlin and Watson, 2006); although their contribution is not well understood.
In general, both species are assumed to be present in RAS.
Fish can take up GSM and MIB chemicals from tainted waters and
accumulate these in their flesh. The uptake of taste-taint chemicals by fish can
occur through several routes including, gills, skin and alimentary canal.