Growth, feed efficiency and digestibility in salmon (Salmo salar L.) fed different dietary proportions of vegetable protein sources in combination with two fish meal qualities

Summary

This study was performed to evaluate the effect on fish growth performance by replacing fish meal with a blend of vegetable protein sources. Atlantic salmon were fed eight diets where the percentage of protein from fish meal to vegetable protein varied from 85.1%, 68.6%, 51.9% to 34.7%, respectively. The experimental groups were fed in triplicate for 11 weeks, increasing fish weight from about 128 g at start to 450 g in the end. The vegetable protein blend was composed of full-fat soybean meal and corn gluten meal at a 1:2 ratio. Four percentages of fish meal to vegetable protein blend were used in four diets using LT fish meal or medium quality fish meal. All diets were extruded and balanced to be equal in gross energy, crude protein, lipid, carbohydrate, lysine and phosphorus. A significant positive linear correlation between fish meal inclusion and fish growth, feed efficiency and digestibility of protein, lipid and energy was observed in diets containing high quality fish meal. The difference in growth corresponded to a difference in final weight of 13.3% comparing diets with 85.1% and 34.7% fish meal protein. A significant positive correlation between fish meal inclusion and growth and feed efficiency was also observed in diets containing medium quality fish meal. No difference in growth was found between treatments containing the two fish meal qualities (P=0.06). However, feed intake was significantly higher and feed efficiency lower for fish fed medium quality compared to high quality fish meal. Protein, amino acid and energy digestibilities were reduced with increased dietary vegetable protein blend inclusion. Protein efficiency ratio (PER) and net protein value (NPV) were also positively linearly correlated to dietary fish meal percentage, and significant reductions in PER and NPV of 10% were observed as dietary fish meal protein decreased from 51.9% to 34.7%. NPV were in average 6.5% higher in fish fed diets containing high quality fish meal compared to medium quality fish meal. No difference in chemical composition of the fish was observed for any of the diets. A difference in performance was observed for fish meal quality and vegetable blend. The effect of reduced fish meal quality could be explained by reduced digestibility of protein and amino acids. This was compensated by a similar increase in feed intake, reducing NPV for medium quality fish meal. Increased inclusion of vegetable blend affected growth performance and reduced digestibility, but was not compensated by increased feed intake.