Fishmeal intervention after short-term novel proteins stimulates compensatory growth and affects intestinal health in largemouth bass (Micropterus salmoides).

This research utilized a compensatory growth phenomenon aimed at reducing the use of fishmeal in aquatic animal feed. However, the compensatory growth triggered by fishmeal restriction with novel protein replacement has yet to be understood. Five isonitrogenous and isolipidic diets containing different proteins were manufactured, with fishmeal serving as the control and diets containing novel proteins, i.e., Chlorella (Chlorella vulgaris), cottonseed protein concentrate, Clostridium autoethanogenum, and yellow mealworm (Tenebrio molitor), serving as the experimental diets. Largemouth bass (Micropterus salmoides) with a starting body weight of 4.73 ± 0.04 g were respectively fed these five diets for the first 29 days (first stage), followed by a fishmeal diet for the remaining 29 days (second stage). The diet of fishmeal, Chlorella vulgaris, cottonseed protein concentrate, Clostridium autoethanogenum, and Tenebrio molitor was referred to as FM, ChM, CSM, CAP, and TM, respectively. All novel protein groups showed a 60-73% higher weight gain compared to the fishmeal group during the second phase; however, they did not reach the weight level seen in the control group. In addition, the second stage of fishmeal intervention resulted in a reduction of approximately 35% in the area of positive Alcian blue (AB) staining of intestinal tissues in the CSM group, and about 40% in the CAP group, compared to the first stage. Furthermore, the area of intestinal apoptosis in TM was enlarged after fishmeal intervention while it was decreased in other experimental groups. At day 58, gene expression analysis of the CAP group fish at the end of the trial revealed increased levels of the anti-apoptotic gene bcl-2, as well as higher expression of intestinal inflammatory cytokines il-1β, tnf-α, nf-κb p65, and il-10, compared to the FM group. In terms of the biochemical indices, the levels of catalase (CAT) and glutathione peroxidase (GSH-Px) were reduced in CSM on day 58. An assessment of potential microbial function at end of trial demonstrated that CAP could reduce the lipid metabolism and amino acid metabolism, and increased carbohydrate metabolism pathways in the largemouth bass intestine. In conclusion, both CAP and ChM groups showed promise to reduce fishmeal with respect to intestinal health rather than growth. This study should be of value to practitioners wishing to use novel proteins to reduce fishmeal via the utilization of the compensatory growth phenomenon.