Feed containing heat-killed lactic acid bacteria as a single species or multispecies combination improves feeding, defense, and stress in coho salmon.

There are few reports examining the effects of simultaneous administration of multiple killed lactic acid bacteria with different physiological properties to fish. In this study, we fed three heat-sterilized lactic acid bacteria, Lactobacillus delbrueckii (Lac-b-d), Leuconostoc mesenteroides (Leu-m), and Lactococcus lactis (Lac-c-l), either singly or in combination (Combination), to juvenile coho salmon Oncorhynchus kisutch for 4 weeks and examined the changes in the physiological responses of the fish. At a daily bacterial intake of 0.1 mg/kg BW, granulocyte increased in the Leu-m, Lac-c-l, and Combination groups; lymphocyte increased in the Lac-c-l group; and granulocyte phagocytic activity was higher in the Lac-b-d and Combination groups. In a 4-week feeding experiment in which the intake of the multispecies Combination was varied, a feeding attraction effect was found in the 0.05 and 0.1 mg/kg BW/day groups, red blood cell and lymphocyte counts, granulocyte phagocytic activity, and potential killing activity were significantly higher in the combination group than in the control group. The survival rate in hypoxic conditions was also remarkably higher in the 0.05 and 0.1 mg/kg BW/day combination groups. These results suggest that the administration of multiple heat-killed lactic acid bacteria is effective in improving the physiological responses of fish.