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 microg 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. 2009 Elsevier Ltd.