Probiotics have shown beneficial effects on growth parameters of various food animals. In this research, the growth promoting effects of a multi-strain probiotic was investigated on common carp (Cyprinus carpio). Accordingly, 200 fish (6-7g) were randomly allocated to 4 experimental groups. The first group received placebo and was served as the negative control. The second group received the prebiotic Fermacto at 3g/kg diet and was considered as the positive control. The remaining 2 groups received a multi-strain probiotic (PTX) at 75 and 150mg/kg feed, respectively. The body weights and lengths of all fish were measured at the end of the experiment (day 45). The amounts of protein, fat, ash and dry matter of fish meat were analyzed in all experimental groups (n= 6 each). The probiotic, at 75mg/kg feed, significantly increased the body weights and lengths, as well as the condition factor. Consistently, the feed conversion rate was lower in PTX treated groups. The percentage of meat fat was significantly lower in groups receiving either the probiotic at 150mg/kg feed, or Fermacto, compared to the control. The fish receiving PTX at 150mg/kg feed showed significantly higher amounts of meat protein. The levels of meat ash and meat dry matter were not statistically different compared to the control group. The present study suggests that PTX, at 75mg/kg feed, is effective in improving the growth and feed conversion rates of common carps

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