Development of protection in rainbow trout (Oncorhynchus mykiss, Walbaum) to Vibrio anguillarum following use of the probiotic Kocuria SM1

Probiotic Kocuria SM1, which was part of the allochthonous gut microbiota of rainbow trout, was administered to rainbow trout (Oncorhynchus mykiss) fingerlings as dietary supplement at ∼108 cells g−1 for two weeks. The fish were challenged with Vibrio anguillarum and innate immunity determined over the following 5 weeks. The probiotic-fed fish survived (mortalities = 10–28%; P less than 0.05) better than the controls (mortalities = 73–92%) for 5 weeks after stopping administration of Kocuria SM1, although the relative percent survival (RPS) declined steadily from 87 to 36% by the end of the experiment. A significant (P less than 0.05) effect on the immune parameters was observed in fish within 3 weeks after stopping administration of Kocuria SM1 in comparison with the controls, i.e. enhancement of the respiratory burst (OD550nm) from 0.051 ± 0.014 to 0.067 ± 0.009, lysozyme 605 ± 185 units ml−1 to 872 ± 114 units ml−1, total protein 19.8 ± 2.0 mg ml−1 to 23.8 ± 0.8 mg ml−1 at 2 weeks, and leukocrit 2.9 ± 1.8% to 5.1 ± 1.1%, peroxidase (OD550nm) 0.23 ± 0.02 to 0.37 ± 0.11 and bacterial killing activities (percentage of surviving bacteria = 82 ± 12% to 57 ± 4%) at 3 weeks. Generally, the levels reduced progressively towards the end of experiment