Abstract:An 8-week feeding trial was conducted to investigate the effects of different types of protein hydrolysate in high plant protein diets on the lipid accumulation of juvenile Japanese seabass Lateolabrax japonicus (initial body weight 31.99 g). Four experimental diets were formulated. The control diet contained 30% fishmeal. Different types of protein hydrolysate, i.e., pig blood protein hydrolysate, soy protein hydrolysate and yeast protein hydrolysate was separately added to the basal diet to replace 10% fishmeal to formulate three experimental diets. The feeding trail was conducted in sea floating net cages. Each diet was assigned to triplicate groups of 30 fish. The results showed that compared to the control group, the supplementation of protein hydrolysates from pig blood, soybean meal and yeast did not significantly influence most indices of lipid accumulation in L. japonicus. However, compared to the control group, the yeast protein hydrolysate significantly reduced the concentrations of triglyceride, cholesterol, and low density lipoprotein cholesterol in serum (P<0.05). The fatty acid analysis showed that compared to the control group, the yeast protein hydrolysate significantly increased the C20:1n-9 content in muscle, while the soy protein hydrolysate and yeast protein hydrolysate significantly reduced the C22:5n-3 content in muscle (P<0.05). Compared to the control group, the yeast protein hydrolysate significantly reduced the C20:5n-3 content in serum (P<0.05). In adipose tissue, compared to the control group, the protein hydrolysates from pig blood, soy, and yeast significantly increased the contents of saturated fatty acids, ≤18C monounsaturated fatty acids, linoleic acid and linolenic acid, but significantly reduced the contents of C20:1n-9、C20:4n-6、C22:5n-3 and C22:6n-3 (P<0.01). These results suggested that in high plant protein diets the supplementation of protein hydrolysates from pig blood, soy, and yeast did not modulate the lipid accumulation in whole body, liver, muscle and gut of juvenile L. japonicus, but the yeast protein hydrolysate significantly reduced the concentrations of triglyceride, cholesterol, and low density lipoprotein cholesterol in serum. The modulation of fish fatty acid profiles by protein hydrolysates varied depending upon the type of protein hydrolysate and the type of fish tissue. This is the first study comprehensively investigating the effects of different types of protein hydrolysate on the lipid accumulation in aquaculture species, and the results were indicative for the relevant studies in the future.
