VARIATION IN THE OPERATING INCOME AND THE ENVIRONMENTAL-IMPACT OF TROUT CULTURE FROM A DANISH FISH FARM UTILIZING DIFFERENT PRODUCTION STRATEGIES

The age at which fish are transferred to seawater and the feeding stra tegies employed during the breeding season affect the economics underl ying production of rain trout, as well as the environmental loading of phosphorus and nitrogen. An experiment was undertaken to evaluate the effects of i) age at seawater transfer, ii) feeding level and iii) us e of a finishing feed, upon production economics. Monosex female rainb ow trout (500-900g grown to 3500g) transferred to seawater at either 1 or 2 years of age, were examined. Feeding level was either that norma lly used by the farm or reduced by 20%. A commercial feed type with a protein-fat content of 48-28% was used throughout the experiment. Seve n weeks prior to slaughter, fish were placed on a finishing diet with a protein-fat content of 60-9%. A set of economic-environmental models were established to evaluate the effects of the different production protocols upon farm profitability. Calculations were based upon fish p erformance evaluated as daily growth rate (% body wt/d), feed conversi on rate, mortality, and weight data by means of visceral loss and gona dal development. The results of the present study illustrate that it i s not possible to optimize both environmental impact and economic bene fit during the production of trout.