Characteristics of growth, digestive system functionality, and stress factors of rainbow trout fed probiotics Kocuria SM1 and Rhodococcus SM2

The effects of dietary probiotics on growth performance, health status of the digestive system and on the blood parameters of juvenile rainbow trout (Oncorhynchus mykiss, Walbaum) were investigated. Compared to the controls, diets supplemented with Kocuria SM1 and Rhodococcus SM2 for 14 days caused no significant (P > 0.05) change on the growth of fish, although SM2 led to an increased specific growth rate. SM1 or SM2 started to colonize in the gut after 7 days of administration reaching a maximum, i.e. ~ 90-100% of total bacterial population, at 14 days. Yet, the probiotics disappeared from the gut once administration ceased. Structural differences were not noted in the pyloric caeca and foregut, but the overall condition of the midgut and hindgut improved in fish receiving probiotics. The profile of digestive enzymes, as determined by the use of API ZYM, and stress indicators, i.e. serum hemoglobin, urea, creatinine and glucose, was not affected by any of the experimental diets (P > 0.05).