Antagonism of Aeromonas hydrophila by propolis and its effect on the performance of Nile tilapia, Oreochromis niloticus

Propolis, a resinous substance collected by Apis mellifera bees from various plant sources and mixed with secreted beeswax, is a multifunctional material used by bees in the construction, maintenance, and protection of their hives. The collected propolis sample, from High Egypt, was dark-green with olive-odor. The minimal inhibition concentration (MIC) of propolis-ethanolic-extract, against Aeromonas hydrophila, was 80 mu g Propolis-ethanolic-extract and crude propolis (1%) were added to artificial basal diet with (30% crude protein) to evaluate their efficacy on the fish growth-performance, immunostimulation and resistance to A. hydrophila. Two hundred and twenty-five Oreochromis niloticus (8 +/- 0.45 g/fish) were divided into three equal treatments (T) of triplet replicates. The fish of T-1 were fed on basal diet (control). The fish of T-2 were given the basal diet, containing propolis-ethanolic-extract. The fish of T-3 were given the basal diet containing crude propolis for 28 day. The fish were intraperitoneally challenged by A. hydrophila (0.2 x 10(7) cells ml(-1)) at the end of the feeding period and kept for 15 more days. The best growth rate and feed conversion ratio were obtained with T-2. The increase in the average daily gain, specific growth rate and feed efficiency ratio were highly significances in T-2 followed by T-3 when compared with the control group. The HCT-level and monocyte-counts were increased (T-2). No significant change, in the large lymphocytic-count was found among the three treatments (28-27-28%), while the neutrophil-count was significantly decreased (7%) with T-2 and increased (13.11%) with the control. A significant increase in serum lysozyme and serum bactericidal activities was found with T-2. The RLP against A. hydrophila was high with T-2 and T-3. The propolis-ethanolic-extract enhanced the growth, immunity and resistance of O. niloticus against A. hydrophila more than the crude propolis. (C) 2009 Elsevier Ltd. All rights reserved.