The Optimized Inclusion Level of Bacillus Subtilis Fermented Azolla Pinnata In Nile Tilapia (Oreochromis Niloticus) Diets: Immunity, Antioxidative Status, Intestinal Digestive Enzymes and Histomorphometry, And Disease Resistance

Abstract

<title>Abstract</title> A 95-day feeding trial was conducted to evaluate the outcomes of feeding <italic>Bacillus subtilis</italic> fermented <italic>Azolla (BSFA)</italic> on nonspecific immunity, antioxidative status, intestinal digestive enzymes and histomorphometry, and disease resistance in the Nile tilapia. We formulated five isonitrogenous and isocaloric experimental diets to incorporate <italic>BSFA</italic> at (0%, 15%, 30%, 45%, 60%). The growth performance parameters (<italic>FBW, BWG, SGR, PER</italic> and <italic>FCR</italic>) revealed a significant increase in the <italic>BSFA30</italic> tilapia group compared to the control group followed by <italic>BSFA45</italic> (<italic>P &lt; 0.05</italic>). The <italic>BSFA30</italic> group exhibited the highest nonspecific immunity parameters (lysozyme activity, phagocytic index and phagocytic activity) compared to other groups (<italic>P &lt; 0.05</italic>). SOD and GPx reported the highest values in the <italic>BSFA60</italic> group. Nile tilapia carcass composition was not influenced by <italic>BSFA</italic> inclusion level (<italic>P ˃ 0.05</italic>). Interestingly, Nile tilapia fed with <italic>BSFA15 </italic>diet exhibited the highest protease activity level <italic>(P </italic>˂<italic> 0.05)</italic>, while those fed on <italic>BSFA30 </italic>documented the highest amylase activity. Intestinal histomorphology was significantly enhanced with the gradual increase of administrated <italic>BSFA</italic>. Tilapia disease resistance against <italic>A. septicemia</italic>, <italic>BSFA </italic>significantly diminished the cumulative mortality compared to the control group. To sum up, <italic>BSFA</italic> was more effective in improving the growth performance and immunity of Nile tilapia.