Evaluation of three fish-derived probiotic bacteria replacing antibiotics on growth, immunity, gut morphology and disease resistance in juvenile olive flounder Paralichthys olivaceus fed reduced fish meal diets

Wonsuk Choi ¹ Mohammad Moniruzzaman ^2* Seunghan Lee ³ Jinho Bae ⁴ Sungchul Charles Bai ¹ Taesun Min ² Seunghyung Lee ¹

• ¹ Pukyong National University, Busan, Republic of Korea
• ² Jeju National University, Jeju City, Republic of Korea
• ³ Kunsan National University, Gunsan, North Jeolla, Republic of Korea
• ⁴ National Institute of Fisheries Science (NIFS), Busan, Busan, Republic of Korea

A basal diet without feed additives was used as a control (CON) and three diets were formulated by supplementing with Bacillus subtilis WB60 at 1×10 8 CFU/g (Pro-A), B. subtilis SJ10 at 1×10 8 CFU/g (Pro-B), Enterococcus faecium SH30 at 1×10 7 CFU/g (Pro-C), and two other diets supplementing with antibiotics such as amoxicillin (AMO) at 4 g/kg and oxytetracycline (OTC) at 4 g/kg of the basal diet. A total of 450 fish averaging 12.1 g were fed one of the six diets in triplicates for 8-week. Weight gain, specific growth rate and feed efficiency of fish fed the Pro-A diet were significantly greater than those of fish fed the CON, OTC and AMO diets (P< 0.05). Furthermore, feeding efficiency and protein efficiency ratio of fish fed the Pro-A diet were significantly greater than those of fish fed the CON, OTC and AMO diets. Serum aspartate aminotransferase levels were significantly greater in fish fed the Pro-B diet than in those fed the Pro-A diet. The lysozyme activity of fish fed the Pro-A, Pro-B and Pro-C diets was significantly greater than that of the CON, OTC and AMO diets. The myeloperoxidase activity of fish fed the Pro-A diet was significantly greater than that of the fish fed the CON and AMO diets. The flounder growth hormone levels of fish fed the Pro-A, Pro-B, Pro-C and AMO diets were significantly greater than that of the fish fed the CON diet. The interleukin 1β gene expression levels in fish fed the Pro-B and Pro-C diets were significantly greater than those in fish fed the CON, OTC and AMO diets. The interleukin 10 gene expression levels in fish fed the Pro-A, Pro-B, Pro-C and OTC diets were significantly greater than those of fish fed the CON and AMO diets. Intestinal histology revealed that the average villi length of fish fed the Pro-A, Pro-B, and Pro-C diets were significantly greater than that of fish fed the CON, OTC and AMO diets. The cumulative survival rates of fish fed the Pro-A, Pro-B and Pro-C diets were significantly greater than those of fish fed the CON diet.