Effects of dietary supplementation of Gracilaria lemaneiformis-derived sulfated polysaccharides on the growth, antioxidant capacity, and innate immunity of rabbitfish (Siganus canaliculatus).

The dietary supplementation of red seaweed-derived polysaccharides has been shown to be beneficial to fish and shellfish aquaculture. However, the function of red seaweed (Gracilaria lemaneiformis)-extracted polysaccharide (GLP) on the health status of rabbitfish (Siganus canaliculatus) is still unknown. This study explored the influences of GLP on growth performance, antioxidant activity, and immunity of rabbitfish. Herein, the fish were fed commercial pelleted feed incorporated with the diverse amount of GLP: 0 (control), 0.10 (GLP0.10), and 0.15 g kg-1 (GLP0.15) for 60 days. The results demonstrated that dietary GLP0.15 significantly elevated FBW and WG, while feed utilization efficiency improved (reduced feed conversion ratio and increased protein efficiency ratio) upon GLP0.10 treatment, regarding the control (P < 0.05). Also, dietary administration of GLP0.15 suggestively improved the serum acid phosphatase and lysozyme activity as well as hepatic total antioxidant capacity, catalase, and superoxide dismutase activity. In contrast, GLP0.15decreased the serum alkaline phosphatase, aspartate aminotransferase, alanine aminotransferase, and malonaldehyde activity when compared to the control (P<0.05). Moreover, the lipase (36.08 and 16.46 U/mgprot in GLP0.10 and GLP0.15, respectively) and amylase (0.43 and 0.23 U/mgprot in GLP0.10 and GLP0.15, respectively) activity recorded the maximum values than the control (8.61 and 0.13 U/mgprot, respectively).Further, the intestinal morphometry was developed (such as increased villus length, width, and area) in the fish fed with a GLP-supplemented diet compared to the control. The KEGG pathway analysis unveiled that several differentially expressed genes (DEGs) in control vs. GLP0.10 and control vs. GLP0.15 were associated with metabolic or immune-associated pathways like antigen processing and presentation, phagosome, complement and coagulation cascades, and platelet activation. The DEGs, namely C3, f5, fgb, MHC1, and cfb, were evaluated in control vs. GLP0.10 and C3 and MHC1 in control vs. GLP0.15, suggesting their possible contributions to GLP-regulated immunity. Additionally, the cumulative mortality of rabbitfish after the Vibrio parahaemolyticus challenge was lower in both GLP0.10 (8.88%) and GLP0.15 (11.11%) than in control (33.33%) (P<0.05). Thus, these findings direct the potential use of GLP as an immunostimulant and growth promoter in rabbitfish aquaculture.

Effects of prebiotic mixtures on growth performance, intestinal microbiota and immune response in juvenile chu's croaker, Nibea coibor.

Prebiotics has been known to be growth promoter and immunostimulant in aquatic animals. In this study, we investigated the effects of prebiotics on growth performance, intestinal microbiota, short-chain fatty acids (SCFAs) production and immune response of the marine fish, juvenile chu's croaker (Nibea coibor). The fish were fed IG (including 0.5% inulin and 0.5% GOS), GS (0.5% GOS and 0.5% D-sorbitol), IGS (0.33% inulin, 0.33% GOS and 0.33% D-sorbitol) or control diets for 8 weeks. The results showed that the growth performance of the fish was promoted by IG and GS, but not by IGS. The intestinal microbiota in NDC (non-digestible carbohydrates, NDC)-supplemented groups was clearly separated from that of the control, and the highest Shannon and Simpson diversity indices were observed in the IGS group. In the intestine of the croaker, Proteobacteria, Firmicutes, and Bacteroidetes were dominant; among them, 24 taxa revealed a significant difference among groups. Most of these bacteria are able to produce SCFAs, which were significantly increased in all NDC-supplemented groups. Moreover, NDCs were found to activate the immune system of the fish by modulating the serum complements, cytokine levels, lysozyme activities and antioxidant capacity. Furthermore, the results of this study revealed correlations among intestinal microbiota, SCFAs production, innate immunity, antioxidant capacity and digestive enzymes in the croaker fed NDCs. Taken together, our results demonstrated that NDC mixtures might promote growth performance, antioxidant capacity and immune responses of the croaker through modulating the composition of intestinal microbiota and the subsequent SCFAs production, which suggest that NDCs were efficient feed additives for marine fish.