Replacement of dietary fish meal with soy protein concentrate on the growth performance, PI3K/AKT/TOR pathway, immunity of abalone Haliotis discus hannai and its resistance to Vibrio parahaemolyticus

Five isonitrogenous and isolipidic experimental diets were formulated to investigate the influence of soy protein concentrate (SPC) replacing dietary fish meal (FM) on the growth, PI3K/AKT/TOR pathway, immunity of abalone Haliotis discus hannai and its resistance to Vibrio parahaemolyticus. The basal diet was designed with 20 % of FM. Based on it, the FM was replaced by SPC at 0 (CON), 25 % (SPC25), 50 % (SPC50), 75 % (SPC75) and 100 % (SPC100), respectively. After the 110-day feeding trial, it was shown that completely replacing FM with SPC had no adverse effects on growth, feed utilization and body composition of abalone. The highest weight gain rate of abalone was 119.52 %, which was observed in the SPC25 group. The trypsin activity in the digestive gland within the SPC25 and SPC50 groups exhibited a significant increase compared to that in the remaining groups. Relative to the CON group, the SPC100 group showed a significant reduction in total antioxidant capacity and an increase in malondialdehyde content within the cell-free hemolymph (CFH). The myd88 mRNA expression in the SPC25-SPC75 groups was significantly decreased compared with other groups. The highest expressions of pi3k, mtor and s6k, and the lowest expression of 4e-bp were found in the SPC25 group. The hardness of muscle was significantly increased with the increasing dietary SPC levels. The CON, SPC25, and SPC50 groups exhibited significantly lower cumulative mortality rates among abalones following the V. parahaemolyticus challenge. In conclusion, in terms of growth, FM can be totally replaced by SPC. Furthermore, replacing 25 % of dietary FM with SPC led to a significant enhancement in abalone growth. Moderately replacing FM with SPC (up to 50 %) could improve abalone digestive capacity and did not significantly affect abalone survival following a V. parahaemolyticus challenge. The optimal replacement level of FM by SPC (≤ 25 %) triggered the PI3K/AKT/TOR pathway to promote protein synthesis. Considering the growth, digestion, immunity, muscle quality and disease resistance of abalone, it is recommended that dietary FM can be replaced by SPC not more than 50 %.