Effects of compound feed attractants on the growth rate, feed consumption, intestinal histology, protein synthesis, and immune response of black tiger shrimp (Penaeus monodon)

Feed intake is a crucial factor in promoting aquatic animals' robust and accelerated growth. Recently, plant protein has been used extensively as a replacement for fishmeal in aquaculture diets, potentially causing adverse effects on both feed palatability and animal health. However, incorporating suitable quantities of feed attractants into the diet can enhance feed palatability, stimulate the appetite of aquatic animals, and potentially augment both growth and overall health. A study was conducted to assess the efficacy of various feeding attractant combinations on Penaeus monodon. In this study, these seven diets were formulated consisting of a positive control (labeled as P) based on commercial feed, a negative control (labeled as N) with a low level of feed attractants, and five diets (labeled as A, B, C, D, and E) containing 8% compositional feed attractants. Each of the five attractants (yeast extract, squid visceral powder, fish soluble, squid paste, and shrimp paste) was added in equal amounts to A-E diets. The results showed that compared to the E diet, the A diet significantly improved the final body weight, specific growth rate, weight gain, and feed intake of shrimp and upregulated the expression of pi3k, eif4ela, and raptor in hepatopancreas. Compared to the P diet, the C diet feed significantly increased the activities of glutamate oxaloacetate transaminase and acid phosphatase and upregulated the expression of pi3k, myd88, and tor in the intestine. In comparison to the N diet, the D diet feed increased the activity of alkaline phosphatase in hemolymph, total superoxide dismutase activity in hepatopancreas, and malondialdehyde content. Additionally, it upregulated the expression of myd88, pi3k, tor, and ror. Compared to the control group, the feed in the E diet increased the total superoxide dismutase activity in the hemolymph and upregulated myd88, pi3k, tor, and imd expression levels. Furthermore, C, D, and E diets increased the width of the shrimp's intestinal folds. Regression analysis showed that the weight gain and feed intake increased with the increasing amount of squid paste in the feed and decreased with the addition of shrimp paste. Feed intake increased with the addition of fish-soluble protein and decreased with the addition of yeast extract in the feed. In conclusion, adding attractants (yeast extract, squid viscera powder, fish soluble, and squid paste) to the feed is beneficial for the growth and feeding of shrimp, and it can promote the expression of shrimp intestinal immune-related genes and histological changes, thus promoting shrimp intestinal health.