Effect of the probiotic, Lactobacillus plantarum on growth performance and haematological indices of rainbow trout (Oncorhynchus mykiss) immunized with bivalent streptococcosis / lactococcosis vaccine

The present study evaluated the effect of Lactobacillus plantarum as a probiotic on the growth performance and haematological parameters of juvenile rainbow trout (O. mykiss) weighing 29.6±1.8 g immunized with streptococcus/lactococcus vaccine. Fish were randomly allocated into 4 equal groups consisting of fish fed with the probiotic  supplemented in diet (group P), fish immunized with streptococcosis / lactococcosis vaccine and fed with a normal diet (group V), fish immunized with streptococcosis / lactococcosis vaccine and fed with probiotic supplemented in diet (group P+V) and unimmunized fish fed (group C). The probiotic (108cells/g) was used at 1 g ∕ kg feed. Results showed that weight gain, final weight, condition factor and thermal-unit growth coefficient were improved in P+V group compared to the control one (P < 0.05).Also, feed conversion ratio in P+V group was lower than other trails (P < 0.05). In addition, white blood cell population (WBC) in groups V and P+V were significantly higher than both P and C groups (P < 0.05). Also PCV was significantly increased (P <0.05) in both P and P+V groups compared to V trail and control group. In addition, RBC and Hb levels were significantly higher (P < 0.05) in group P+V than control one. No significant difference (P > 0.05) was found in MCH, MCHC and MCV levels among the different experimental groups.  Hence, application of probiotic can be considered as a beneficial dietary probiotic for improvement of growth performance and some haematological parameters in trout vaccinated against streptococcosis / lactococcosis.