Effects of dietary probiotic, Lactococcus lactis subsp. lactis I2, supplementation on the growth and immune response of olive flounder (Paralichthys olivaceus)

We investigated the effects of a potential probiotic strain Lactococcus lactis subsp. lactis I2 on the immune response and growth of olive flounder (Paralichthys olivaceus), and their capacity to prevent streptococcosis after Streptococcus iniae challenge. The L. lactis subsp. lactis I2 strain, isolated from olive flounder intestine, was supplemented orally as a feed additive (~ 108 CFU g− 1) to fish for 5 weeks. Compared with the untreated group, the rate of growth was increased in the I2-diet group. The administration of I2 to olive flounder enhanced non-specific immune parameters, such as lysozyme, antiprotease, serum peroxidase and blood respiratory burst activities. At 9 days after challenge with S. iniae (108 CFU), the untreated control group experienced a 90% mortality rate, whereas all of the I2-cell-supplemented fish survived. These results show that L. lactis subsp. lactis I2 exerted beneficial effects as a probiotic and has potential as an alternative to antibiotics for the prevention of streptococcosis in aquaculture.

► The growth rate of fish was increased in the I2-cell supplemented group.
► Non-specific immune parameters enhanced in fish supplemented with I2-cell.
► 100% survivability was observed in I2-group after challenge with S. iniae.