Abstract
Synbiotics are a combination of probiotics and prebiotics which are used as functional feed additives in animal diets. The effects of different synbiotics depending on the microorganisms which is used as probiotics and the substrate which is used as prebiotics. In the commercial feed additive secor there are several manufactured synbiotics with different efficacy. Therefore, the present study aimed to investigate the effects of commercial synbiotics containing Lactococcus lactis >1x10" CFU/Kg and starch on growth performance, phenotypic traits and digestive enzyme activities of monosex Nile tilapia, Oreochromis niloticus. A total of 360 appearent healthy monosex tilapia (1,15 0.19 g) were divided into four treatments (three replicates each). The fish were fed a commercial diet supplemented with different levels of synbiotics (0, 1, 2, and 3 g/kg diet) for 45 days. The results revealed that final weight, weight gain, and specific growth rate improved significantly (p < 0,05) in all synbiotics supplemented groups. The dose response study revealed that the polynomial regression is the fit regression model with R2 equal 0.89 and 0.85 with final weight, and specific growth rate, respectively. The dressing percent increased significantly (p < 0.05) with 2 g synbiotic /kg diet compared to other groups. The morphometric evaluation revealed significant improvement in total, standard, and trunk length, and body area in synbiotic supplemented groups. The activities of amylase and protease enzymes in the intestine increased significantly with increasing synbiotics supplementation. It is recommended to use POWER LAC' synbiotics at levels of 2 g/kg diet to improve growth performance. phenotepic traits and digestive enzyme activities.