Abstract
Probiotics and herbals are highly recommended in aquaculture; however, little is known about their combined effects. Therefore, the present study evaluated the possible synergistic impacts of Spirulina platensis (SP) and Bacillus amyloliquefaciens (BA) on the growth performance, histomorphology, and immune response of Nile tilapia (Oreochromis niloticus). A control and three test diets were enriched with SP, BA, or both SP and BA and fed for tilapia for 60 days. The obtained results displayed higher final body weight, weight gain, and specific growth rate in fish fed SP or/and BA with respect to the control with the highest being in fish fed both SP and BA (P < 0.05). The feed conversion ratio was lower in fish fed SP or/and BA with the lowest being in fish fed both SP and BA (P < 0.05). In the three intestinal segments, the mucosal length, villi length, and number of goblet cells were increased by dietary SP or/and BA (P < 0.05). The histological structure of the intestinal villi revealed increased length and regular structure which confirm that the tilapia intestine is out of inflammation. The biochemical variables displayed non-significant differences among the groups with normal values. The blood total protein and immunoglobulin M were significantly higher in fish fed BA alone or both SP and BA than fish fed the control (P < 0.05). The mRNA level of TNF-alpha gene was significantly increased by dietary SP or/and BA with respect to the control group while HSP70 was decreased (P < 0.05). The transcription of SOD was higher in fish fed both SP/BA than the other groups (P < 0.05). The obtained results revealed the importance of including both SP and BA in tilapia diets to enhance the growth rate, intestinal histomorphology, and health status.