Streptomyces kunmingensis XK9 and galactooligosaccharide synergistically enhance growth performance, nonspecific immunity and disease resistance in striped catfish (Pangasianodon hypophthalmus)

The present study evaluated the effectiveness of the synergy of Streptomyces kunmingensis XK9 and galactooligosaccharides (GOS) in improving growth performance, nonspecific immunity, and protection of striped catfish (Pangasianodon hypophthalmus). Seven feed regimens were tested in striped catfish fingerlings, including commercial pellets supplemented with preparations S7, S8, and S9 containing XK9 at 10(7) CFU/mL, 10(8) CFU/mL, and 10(9) CFU/mL, respectively; G5 containing 5% GOS; S7G5, S8G5, and S9G5 including 5% GOS and XK9 at different doses of 10(7) CFU/mL, 10(8) CFU/mL, and 10(9) CFU/mL, respectively. After 3 months of treatment with different dietary regimens, weight gain, specific growth rate, weight gain rate, and feed conversion ratio were greatly improved in fish-fed diets containing S9, S8G5, and S9G5 (p<0.05). Nonspecific immune parameters, including total white blood cell, phagocytic activity, and phagocytic index, increased consistently in fish that were fed diets containing synbiotics S8G5 and S9G5 (p<0.05). Lysozyme and complement activity increased substantially in fish that were fed diets supplemented with S9G5 (p<0.05). The protective effect of XK9 and GOS on striped catfish was evaluated after 15 days of challenge with Edwardsiella ictaluri. The results achieved show that the cumulative mortality rate sharply decreased in fish fed a diet containing the synbiotic S9G5, down 2.17 times compared to the control group; pathogen density was lowest in tanks of fish that were fed regimens containing S8G5, S9G5, and S9 (p<0.05). The results suggest that synbiotics, including S. kunmingensis XK9 and GOS, have the potential to be applied in sustainable farming for the striped catfish industry.<br />