Effect of dietary supplementation of some immunostimulants on growth performance, profitability and disease resistance of Nile tilapia (O. niloticus) fries reared in hapa-in-pond system under

To evaluate the effect of some immunostimulants on growth performance parameters, survival rate and diseases resistance of Nile tilapia fry reared under different stocking densities, a total number of 2250 Oreochromis niloticus fries (0.3 ±0.05 g) were stocked at (2, 4, and 6 fry/m3) and provided with dietary supplementation of (Garlic 40 g/kg, purpurea extract 4 g/kg, Organic GreenTM 4 g/kg and Vet-YeastTM 4 g/kg of the diet) for a five-month period. The obtained results indicated that, stocking fries at 6 fry/m3 adversely affect fish growth performance (fish weight gain, condition factor, specific growth rate) that could be reserved by using Vet-YeastTM and garlic while Echinacea purpurea gave the best feed conversion ratio either in lower or higher density stocked group. The adverse effect on survival rate of fish stocked with (6 fish/m3) could be reserved by using garlic and Vet-YeastTM. In addition, relative protection levels against Aeromonas hydrophila (A. hydrophila) and Pseudomonas fluorescens (P. fluorescens) challenge were higher in groups supplemented with garlic, Echinacea purpurea followed by Vet-YeastTM supplemented group either with low or high stocking density. It could be concluded that, the addition of immunostimulants especially garlic, Echinacea purpurea and yeast to the diet of O. niloticus fry could improve growth performance, fish survival, and overcome the adverse effect of high stocking density.