Waste production by farmed atlantic halibut (Hippoglossus hippoglossus L.)

Abstract The assessment of the acceptable level of fish farm development in Scottish coastal areas is strongly dependent on the predicted rate of release of nitrogenous nutrients and particulate organic waste. A mass balance model of 4-week resolution has been used to estimate the rate of production of dissolved and particulate waste by cultivated halibut ( Hippoglossus hippoglossus L.). The predicted release of dissolved nitrogen is 48 kg N/t of fish produced and that of particulate organic waste is 150–200 kg/t production. Modelled biomass-specific rates varied within a range of a factor of about three during the growing cycle, averaging 8.3 mg of dissolved N/kg biomass of fish/h and 28.8 mg/kg/h of faeces. There is experimental evidence to indicate potential for future developments to lead to significant improvements in feed utilisation by halibut in cages and an accompanying reduction in waste output. Comparisons with experimental data highlight areas where discrepancies between model and measured values indicate that further studies are required. Research targets include the partitioning of dissolved nitrogen between ammonia, urea and other soluble compounds, and the effects of growth rate and feed utilisation efficiency on waste production.