DIETARY PROTEIN AND LIPID LEVELS ON GROWTH, PHYSIOLOGICAL METABOLISM AND ORGANOLEPTIC QUALITY OF TRIPLOID RAINBOW TROUT

The study was conducted to estimate the effects of dietary protein and lipid levels on the growth performance, physiological metabolism, and organoleptic quality of triploid rainbow trout weighting 1.5 kg. Nine diets were formulated with three levels of dietary protein (P) (35%, 40%, and 45%) and three levels of lipid (L) (20%, 25%, and 30%) using a 3×3 factorial design. In freshwater cages, 13500 adult female triploid rainbow trout (1.5 kg) were cultured for 8 weeks. Triplicate cages (500 fish per cage) were used as repetitions of each experimental diet. Results showed that the P40L25 and P40L30 groups exhibited the highest weight gain rate, and P40L30 groups showed the lowest feed conversion ratio. High protein diet (45%) reduced lipid deposition in the viscera and promoted liver health, evidenced by lower viscerosomatic and hepatosomatic indices, decreased hepatic lipid content, and favorable plasma lipid profiles, along with higher hepatic lipoprotein lipase and total lipase activities. Additionally, a high lipid diet (30%) could increase fillet lipid content but not hepatic lipid content and enhanced liver antioxidative capacity. However, the group fed a diet with 45% protein and 30% lipid exhibited oxidative damage in the intestine, resulting in reduced digestion efficiency and subsequent decreases in growth and feed utilization. In addition, this group had the highest fillet redness value. Dietary lipid level did not affect fillet texture and odor, while high protein diet (45%) compromised fillet texture, characterized by higher fracturability and lower springiness. In total, for triploid rainbow trout weighting from 1.5—2.5 kg, the recommended P and L level based on growth performance was 40% and ≥25%, P and L based on feed utilization was 40% and ≥30%, P and L based on organoleptic quality was 40% and ≥20%, respectively. These results provide a basis for the establishment of a nutritional database and the development of an efficient and environmentally diet for triploid rainbow trout.