Abstract
The present study evaluated the effect of Lactobacillus plantarum as a probiotic on the growth performance and haematological parameters of juvenile rainbow trout (Oncorhynchus mykiss) weighing 29.6±1.8 g immunized with streptococcus/lactococcus bivalent vaccine for 60 days at 16±1.5ºC. Fish were randomly allocated to 4 equal groups: probiotic (g kg-1 feed equal to 108 cells g-1) supplemented diet group (group P), vaccinated fish fed with a normal diet (group V), vaccinated fish fed with probiotic (group P+V) and unvaccinated fish fed normal diet (group C). Results showed that weight gain, final weight, condition factor and thermal-unit growth coefficient were improved in P+V group compared with other groups but was significantly different from groups V and C (p<0.05). Also, feed conversion ratio in the P+V group was lower than other trails (p<0.05). In addition, white blood cell count (WBC) in groups V and P+V were significantly higher than in 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 group V and the control group. No significant difference (p>0.05) was found in RBC, Hb, MCH, MCHC and MCV levels among the different experimental groups. These data show that application of L. plantarum could be a benefit of vaccinated trout, enhancing fish growth and haematological parameters