EMPIRICAL INVESTIGATIONS ON GROWTH OF POST-SMOLT ATLANTIC SALMON (SALMO-SALAR L) IN LAND-BASED FARMS - EVIDENCE OF A PHOTOPERIODIC INFLUENCE

The growth rates of post-smelt Atlantic salmon (Salmo salar L.) at four commercial and two experimental-scale land-based farms in southern Norway were estimated, These farms are among the first land-based salmon grow-out systems that are operated in Norway. The fish were reared in various sized circular tanks, and neither feeding regimes, water quality nor stocking densities were considered to have limited growth rate at any time during the study. A seasonal variation in growth rate was evident at all the study farms. Growth rate in fish subjected to natural daylight was depressed during the autumn and winter. Conversely, no such growth depression in winter was determined at the farm using a continuous light regime. The relationship between growth rate and possible explanatory variables (fish size, water temperature and photoperiod) was analysed and quantified using multiple regression analysis. The results demonstrated clearly that growth in post-smelts in land-based farms was strongly influenced by photoperiod. This commercial-scale work confirms results from experimental studies reported by several authors.