Abstract

Lactic acid bacteria (LAB) were isolated from the intestine of Oreochromis niloticus and its effect, along with that of inulin and fulvic acid, on growth of the same species was determined. Characterization of the isolates was performed through assessing the Gram stain, morphology, cell arrangement, hemolytic activity, antagonism, growth, hydrophobicity, extracellular enzyme activity, and counting of colony forming units (CFU), to select those microorganisms with probiotic potential. The selected isolates were identified at the molecular level by the amplification of 23S and 5S ribosomal genes. Treatments were performed in triplicate in plastic tanks with 600 l of filtered fresh water and 12 fish per tank (1.3 ± 0.12 g): I) Control (commercial diet); II) LAB (5 × 10⁴ CFU/g diet) + 2.5 g inulin + 2.5 g fulvic acid/kg diet; III) LAB (2.5 × 10⁵ CFU/g diet) + 2.5 g inulin + 2.5 g fulvic acid/kg diet; IV) LAB (5 × 10⁵ CFU/g diet) + 2.5 g inulin + 2.5 g fulvic acid/kg diet. We selected three LAB strains, belonging to Pediococcus pentosaceus (LAB 37 and LAB 1-6) and Pediococcus sp. (LAB 35), with probiotic potential. Growth in weight of individuals of treatment III was significantly higher than the control group. Lactic acid bacteria, inulin, and fulvic acid were appropriate growth-stimulating additives for cultured O. niloticus in the concentrations of treatment III.

Key words: Fulvic acid, Oreochromis niloticus, inulin, Pediococcus pentosaceus.