Dietary prebiotics such as 0.5% chitosan, 1% inulin and 0.1% β-glucan have improved the growth, digestion and immune response of different fish species under culture conditions; however, their effects in totoaba juveniles are unknown. In this study, the effects of such prebiotics were evaluated in juvenile T. macdonaldi including measurements of immune response (i.e., leucocyte and respiratory burst in blood) ; digestibility and digestive enzymes (i.e. , trypsin, amylase, and lipase), and RNA-seq transcriptomics of the liver.
Fish fed the chitosan added diet showed the highest respiratory burst, immunoglobulin gene expression , and the lowest lipase activity . Differentially expressed genes analysis resulted in significantly higher expression of proteolysis, digestion, and lipid hydroxylation genes (DEGs, Fig 1). Fish fed the inulin diet showed the highest diet apparent digestibility coefficient, trypsin and lipase activities , and the highest expression of trypsin-like and quimiotrypsin-like genes in the liver . In fish fed the β-glucan diet , DEGs were detected mainly in the category of adaptive immune response (Table 1), with downregulation of immunoglobulins and upregulation of genes of the complement system.
Fish fed the chitosan diet showed the highest number of DEGs, while those fed the β-glucan diet the lowest.
In conclusion, based on the results from the present study, dietary inulin inclusion can improve the digestibility of experimental diets, while c hitosan can stimulate the immune system of juvenile totoaba.