Protective efficacy of dietary rosmarinic acid and Bacillus subtilis on growth, health parameters and resistance against Aeromonas hydrophila in common carp (Cyprinus carpio)

Abstract

Probiotics and polyphenols are the functional ingredients for their antimicrobial, immunomodulatory and growth enhancing properties. However, the combined effects of these additives in fish species have rarely been evaluated. The present study was done to evaluate the effects of Bacillus subtilis probiotic and rosmarinic acid alone or in combination on growth, digestive enzyme activities, serum antioxidant and immune indices as well as disease resistance to Aeromonas hydrophila in juvenile common carp (Cyprinus carpio). A total number of 240 Common carp with mean weight of 13.77 ± 0.78 (mean + SE) were randomly distributed into four groups with three replicates (20 fish per replicate) and fed with 5 × 10⁹ CFU Bacillus subtilis/g feed (BS), 600 mg rosmarinic acid/kg feed (RA), combination of these additives (BS+RA) or the control diet (C) by apparent satiation three times a day for 8 weeks. The results of the present experiment indicated that growth rates, digestive enzyme activities as well as serum immunological parameters were higher in all treated groups, especially BS+RA group, compared to the values achieved in the C group (P < 0.05). Serum biochemical indices, including antioxidant-related enzyme activities were improved in the RA and BS+RA compared to the control fish (P < 0.05). The cumulative mortality rate was 50.00 %, 43.33 % and 40.00 % in BS, RA and BS+RA groups, respectively, compared to 60.00 % mortality in the control fish after challenging with Aeromonas hydrophila (P < 0.05). This study indicated that the eight-week dietary administration of rosmarinic acid and B. subtilis, especially in combination, improved growth rate, digestive enzyme activity, serum immunological and antioxidant responses, and disease resistance to Aeromonas hydrophila in common carp.