Organic loading can stimulate H2S production and reduction in the diversity of benthic fauna (Mattson
and Linden 1983). H2S is soluble in water and has been suggested as the cause of gill damage and other ailments in fish (Beveridge 1987). Unionised H2S is extremely toxic to fish at concentrations that may occur in natural waters as well as in aquaculture farms (Bonn and Follis 1967). Bioassays of several species of fish suggest that any detectable concentration of H2S should be considered detrimental to fish production (Boyd 1979).