Effect of Amorphous Halomonas -PHB on Growth, Body Composition, Immune-Related Gene Expression and Vibrio anguillarum Resistance of Hybrid Grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatu ♂) Juveniles.

Xie, Wei; Ma, Haoran; Gao, Meirong; Du, Dongdong; Liu, Liangsen; Sui, Liying

Simple Summary: Poly-β-hydroxybutyrate (PHB) has proven potential to promote growth and immunity in aquaculture. This study aimed to investigate the effects of adding amorphous Halomonas-PHB to the diet for grouper culture. The findings revealed that supplementation with amorphous Halomonas-PHB did not significantly improve fish growth performance, but it increased the content of fatty acids, including long-chain unsaturated fatty acids C18:1n9, EPA, and DHA in fish muscle. Additionally, it enhanced the resistance of the fish to Vibrio anguillarum possibly by regulating immune-related gene expression in different tissues and organs. These results will contribute valuable insights for the practical application of amorphous Halomonas-PHB in aquaculture. Poly-β-hydroxybutyrate (PHB) is a bacterial metabolite produced by bacteria such as Halomonas sp. that serves as a carbon and energy storage compound for bacteria under nutrient-limited conditions. Two experiments were conducted to investigate the effects of dietary supplementation with Halomonas-PHB on hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatu ♂). In experiment I, juvenile groupers were fed basal diets supplemented with 3% Halomonas-PHB (3% HM-PHB) containing 1.4% PHB and 3% Halomonas (3% HM) without PHB, as well as a control diet, for seven weeks. The results showed no significant difference in survival rate, weight gain, and crude fat content between the 3% HM-PHB group and the control group; however, the crude protein of the 3% HM-PHB group was significantly lower than that of the control group. Furthermore, supplementation with 3% HM-PHB increased the fatty acids content in fish muscles, including long-chain unsaturated fatty acids C18:1n9, EPA, and DHA. In experiment II, groupers were fed a basal diet supplemented with 6.5% Halomonas-PHB (6.5% HM-PHB) containing 3% PHB and 6.5% Halomonas (6.5% HM) containing no PHB, as well as a basal diet (Control). After seven weeks of rearing, the fish were challenged with Vibrio anguillarum for 48 h. Although no significant difference in survival rate and growth was observed among different groups, the dietary supplement of 6.5% Halomonas-PHB improved the survival rate of V. anguillarum challenged grouper and significantly increased the gene expressions of catalase (CAT) and superoxide dismutase (SOD) in blood, interleukin 1 (IL1) and interleukin 10 (IL10) in the liver, spleen, head kidney, and blood (p < 0.05). In conclusion, dietary supplementation of Halomonas-PHB had no significantly positive effect on fish growth performance but increased the content of fatty acids, including long-chain unsaturated fatty acids C18:1n9, EPA, and DHA in fish muscle; it also improved the V. anguillarum resistance, possibly through increasing immune-related gene expression in different tissues and organs. Our findings offer compelling evidence that Halomonas-PHB can be utilized as a feed additive in intensive grouper farming to enhance the groupers' resistance to Vibrio.

UNSATURATED fatty acids; VIBRIO anguillarum; BODY composition; WEIGHT gain; HALOMONAS (Bacteria); EICOSAPENTAENOIC acid; POLY-beta-hydroxybutyrate

Animals (2076-2615), 2024, Vol 14, Issue 18, p2649

2076-2615

Academic Journal

10.3390/ani14182649