Comparative study of three predominant gut Bacillus strains and a commercial B. amyloliquefaciens as probiotics on the performance of Clarias gariepinus

Abstract

The present study was conducted to evaluate the supplementation of three autochthonous Bacillus strains (B. subtilis, B. amyloliquefaciens and B. cereus) and a commercial B. amyloliquefaciensin doses of 1 × 10¹⁰ CFU/kg on the growth performance, hematology, antioxidant activities, digestive enzyme levels, immune status and disease resistance of Clarias gariepinus. A total of 300 fish (75.23 ± 1.6 g) were randomly divided into 5 groups (each group was subdivided into 2 subgroups, 30 fish/each). The control group was fed basal diet (D₀). Diets D₁, D₂, D₃ and D₄were supplemented with B. subtilis, B. amyloliquefaciens, B. cereus and a commercial B. amyloliquefaciens, respectively. During the course of the experiment, D₃ showed the best body weight, weight gain, specific growth rate and food conversion ratio. The measured hemogram blood parameters had the highest significant increase in D_3. WBCs and monocyte counts had no significant differences among the experimental groups. The serum antioxidant and digestive enzymes were the highest in D₃ and were the lowest in D₀. After 15 d, the non-specific immune parameters were markedly increased in fish fed probiotic-containing diet compared with the control. After 30 d, the highest significant immune parameters were observed in D₃; D₁ and D₂ had no significant differences in serum lysozyme activity, nitric oxide and IgM compared with D₀. Myostatin cDNA levels were adversely affected by probiotic supplements compare with the control. The PACAP expression showed the highest significant value in D₃ followed by D₁and D₄then D₂. The relative survival percentages of the Aeromonas sobria challenged C. gariepinus were the highest in D₃, D₂, D₄ and then D₁. Among the three isolated Bacillus species, dietary supplementation with the B. cereus had the highest performance in C. gariepinus compared with the commercial B. amyloliquefaciens and the control group.

Keywords: Antioxidant; Bacillus; C. gariepinus; Digestive enzyme; Growth; Immunity; Myostatin; PACAP.