Towards the identification of a suitable commercial diet for carpione, Salmo carpio L.: a multidisciplinary study on fish performances, quality traits and animal welfare.

Carpione (Salmo carpio L.) is an endangered precious endemism of Lake Garda, whose population has drastically decreased in the past century. Repopulation activities and the economic interest by fisheries for this fish species has driven attention in attempting farming programs. However, to date, several bottlenecks about its culture still remain unsolved, including the identification of a proper growth-out diet. For these reasons, the aim of the present study was to identify and test four different grossly isolipidic,isoproteic and isoenergetic diets in which the protein fraction had a different origin. Specifically, a diet currently used by farmers for carpione (CTRL) characterized by a protein fraction mainly derived from marine ingredients (60%) was used as control. Other three experimental diets were formulated by partially replacing marine ingredients with plant ones (VEG, 70% of the total protein fraction) or with land animal proteins (LAP1 and LAP2, 56% and 68% of the total protein fraction, respectively). The feeding trial was run in triplicate using twelve independent fiberglass tanks (700 L), hosting 40 fish each, and feed was administered ad libitum, 6 days a week, over a three-month period. At the end of the feeding trial, a multidisciplinary approach was used to analyze fish zootechnical performances, nutritional traits, and welfare. The results obtained did not show significant differences in growth performances and feed conversion ratio among the experimental groups. However, fillet quality analyses evidenced significant differences in merchandise flesh features and fatty acid composition of fillets related to the administered diets, including the reduction of polyunsaturated fatty acids related to LAP inclusion. In addition, fish welfare was also affected by the dietary treatments. As regards intestine and liber histology, no significant morphological alterations were observed in CTRL, LAP1, and LAP2 groups, while remarkable histological alterations were observed in VEG group. At molecular level, markers involved inflammation response were triggered by large vegetable percentages, while LAP inclusion played a role in downregulating inflammatory markers expression.In conclusion, a comparative discussion about the effects of the different dietary treatments on carpione production, quality traits and welfare will be performed in relation to the sustainability and the economic impact of the tested ingredients.