Comparative effects of four feed attractants on growth, appetite, digestion and absorption in juvenile Chinese mitten crab (Eriocheir sinensis)

Feed attractants can enhance appetite, increase food intake, and promote digestion and absorption, thereby improving growth. This study investigated the effects of four feed attractants on the growth, appetite, digestion and absorption of juvenile Chinese mitten crab (Eriocheir sinensis). Within the effective dosage range, two concentrations of each feed attractant were added, yielding eight diets and a control diet (Ctrl) without attractants. The attractants included 2.00% and 4.00% squid paste (S1, S2), 0.50% and 1.00% glutamic acid (G1, G2), 0.05% and 0.10% nucleotides (N1, N2), and 0.04% and 0.08% dimethyl-beta-propiothetin (D1, D2). A feed choice behavior test (20 times, six rounds) and an eight-week culture experiment were carried out. All four types of feed attractants demonstrated significant appetite-stimulating effects, enhancing 1-h food intake and increasing the specific growth rate and weight gain. The results of the feed choice behavior experiment were consistent with those of the culture experiment. Among the four attractants, N1, D2, S2, and G2 had effects ranging from high to low at the best concentrations. In addition, this study revealed that appetite-related genes are involved in regulating feeding behavior. Feed attractant supplementation increased feed utilization and crude protein and lipid levels in whole crabs. Notably, feed attractants increased the activity of digestive and absorptive enzymes, with N1 exhibiting the most pronounced effect. Correlation analysis revealed that the specific growth rate and weight gain are associated with food intake, gene expression and enzyme activity, as mentioned above. Dietary supplementation with feed attractants can regulate appetite gene expression to enhance appetite, trigger eating behavior, and ultimately increase food consumption. This study indicated that feed attractants can enhance the activity of digestion and absorption enzymes, facilitate the digestion and absorption of ingested nutrients, improve the utilization and deposition of nutrients, and ultimately promote growth. The findings indicate that a concentration of 0.05% nucleotides is most effective as a feed attractant.