Abstract
The aims of this study were to determine the influence of the factors affecting fin damage under different rainbow trout production systems and to compare the findings with the known experimental reports. The study was based on a questionnaire that included information about the main factors i.e. oxygen level in exit water, water temperature, stocking density, daily feed ration, number of meals and grading frequency on seven rainbow trout farms. Standard multiple regression analysis, based on a previously published fin damage dataset, was used to assess the relationship between the level of fin damage per fin and the factors. Daily feed ration received the strongest weight in the model for the caudal, anal and both pectoral fins, whereas number of meals received the strongest weight in the model for both pelvic fins. Grading frequency received the strongest weight only in the dorsal fin model. Lower levels of daily feed ration and number of meals combined with higher water temperature increased the level of fin damage, whereas stocking density had no effect. The results conform to the experimental research on fin damage in rainbow trout. The research model contributes to the overall assessment of fish welfare and the regression analysis used in this study could be used on rainbow trout farms to evaluate the effect of the main factors on the level of fin damage.