Abstract
An eight-week study was conducted to evaluate the effects of dietary marine protein hydrolysates as fish meal replacements in low-fish-meal diets on the growth performance, feed utilization, and health status of Asian seabass (Lates calcarifer). The high-fish-meal (HFM) diet contained 25% fish meal, while the low-fish-meal (LFM) diet replaced 60% of the fish meal with soybean meal. Three experimental diets were formulated by supplementing the LFM diet with 5% tuna hydrolysate (TH), 2% shrimp hydrolysate (SH), and 5% salmon silage (SS), each replacing an equivalent amount of fish meal. These diets were designated as LFM + TH, LFM + SH, and LFM + SS, respectively. The results showed that the LFM + TH diet significantly improved the percentage of weight gain, average daily growth, specific growth rate, protein efficiency ratio, and feed conversion ratio compared to the LFM diet (p < 0.05), without negatively affecting feed intake or metabolic markers. Histological analysis revealed improved villus length and goblet cell count in the intestine, indicating better nutrient absorption (p < 0.05). However, no significant differences were observed in hematological and immunological parameters, blood plasma metabolic markers, or carcass proximate composition (p > 0.05). Furthermore, the LFM + TH diet exhibited superior survival rates under ammonia stress, highlighting its potential to enhance stress tolerance. These findings suggest that marine protein hydrolysates, particularly 5%TH, can serve as a sustainable and efficient alternative to fish meal protein in diets with up to 60% in soybean meal compensation, promoting better growth and survival in Asian seabass.