Methanotrophic bacterial meal as an alternative feed ingredient for whiteleg shrimp (Litopenaeus vannamei) diets

A nutritional trial evaluated a bacterial single-cell protein (BSCP) as an alternative to fishmeal (FM) in whiteleg shrimp (Litopenaeus vannamei) diets. Four diets with increasing levels of FM replacement (0, 25, 50 and 75 %), which corresponded to an inclusion of 0, 40, 80 and 120 g BSCP/kg feed, were tested in triplicate for 139 days at 27 ºC. Results showed that up to 50 % FM substitution supported optimal whiteleg shrimp growth performance, whereas 75 % FM replacement reduced shrimp growth by 18.1 % (P < 0.05). No differences in terms of survival, apparent feed conversion ratio, whole-body proximate biochemical composition, and the organization and functionality of the digestive system were found among groups (P > 0.05). Higher FM replacement by BSCP (50 % and 75 %) resulted in decreased levels of total n-3 PUFA and DHA in whiteleg shrimp body contents (P < 0.05), which may be corrected by the increasing the levels of fish oil in diets with high levels of BSCP. Fishmeal replacement at 50 and 75 % by BSCP did not modify alpha diversity indices of gut microbiota, whereas gut bacterial community structures were different (P < 0.05). The replacement of FM by BSCP at 75 % (120 g BSCP/kg) tended to enhance disease resistance of whiteleg shrimp against V. harveyi infection, even though this trend was not significant (P = 0.08), while enhanced the activity of antioxidative stress enzymes (P < 0.05), which pointed out potential immunomodulatory effects of BSCP beyond standard nutritional endpoints. The improved activity of antioxidative stress enzymes coupled with the modulation of gut microbiota might explain the increase in disease resistance trend observed in whiteleg shrimp fed higher BSCP levels. While dietary supplementation with methionine and lysine is required to achieve a well-balanced amino acid profile, these findings confirm the promising role of BSCP as a alternative to FM in shrimp diets.