PROBIOTIC EFFECTS OF SELECTED STRAINS OF LACTOBACILLUS PLANTARUM ON THE AFRICAN CATFISH CLARIAS GARIEPINUS (BURCHELL 1822)

Abstract

This research evaluated some probiotic effects of selected strains of Lactobacillus plantarum on Clarias gariepinus. L. plantarum were isolated from fermented maize, sorghum, soybeans and cassava, and characterized using both phenotypic and 16S rRNA sequencing techniques. These strains were further examined for their in-vitro probiotic properties. C. gariepinus broodstocks were artificially induced overnight, while the eggs were stripped and fertilized. An overnight broth culture of selected L. plantarum strains were inoculated into incubating water in 6-litre bowl at bacterial concentration of 2 x103, 2 x 106 and 2 x 109cfu/L. Each treatment was administered in duplicate bowls. Two grammes of C. gariepinus fertilized eggs were incubated in each of these bowls for 30 hours at room temperature, after which hatchability was determined. Water in each bowl was analyzed microbiologically immediately after incubation. The hatchlings’ survivals were evaluated on day 3 and day 10 posthatching. A diet of 40% crude protein was formulated and divided into five portions. The first portion had no probiotic added to it (non-probiotic control) while the second portion contained 2.5 g kg-1 multi-species commercial probiotics. Each of the selected L. plantarum strains was added to three remaining portions to have final bacterial supplementation of 2 x 109cfu/g. Each feed portion was pelletized and stored. Fifteen similar-sized C. gariepinus fingerlings were randomly distributed into 70-litre glass tanks. Each feed (treatment) was administered in triplicate fish tanks. The fish were fed daily at 5 % body weight for 10 weeks. Growth performances, nutrient utilization and digestibility, carcass proximate analysis, haematological and serum biochemical analysis, histological examinations of intestines and livers of the experimental fish were carried out. The experimental fish were challenged with pathogenic bacteria, Pseudomonas aeruginosa, by immersion and their survival evaluated. All data obtained were subjected to one-way ANOVA while significant means were separated using Duncan’s multiple range ad-hoc test at p>0.05. The results of the biochemical characterization revealed that L. plantarum isolates were present in all the fermented foods examined. These isolates were confirmed to be different strains of L. plantarum by 16S rRNA sequencing, having close relatedness (≥ 95%) with other L. plantarum isolates available in the Gene Bank. Three strains of Lactobacillus plantarum were selected for further in vivo study, as they were non-pathogenic, resistant to acidic medium, and possessed antibacterial and enzymatic activities. Inoculation of three selected L. plantarum strains during egg incubation of C. gariepinus significantly (p<0.05) reduced Enterobacteriaecae and fungi counts in incubating water after 30 hours of incubation. Egg hatchability was negatively affected at L. plantarum concentrations of 109 cfu/L. Significantly higher survivals were observed in larvae hatched in water inoculated with 106 cfu/L of L. plantarum strains isolated from fermented sorghum and soybeans. Inclusion of L. plantarum in the diets of C gariepinus fingerlings improved growth, nutrient digestibility and resistance against infection, reduced intestinal microbiota and showed no adverse effect on intestinal and liver morphology and body composition. Strains of L. plantarum isolated from fermented sorghum and soybeans are recommended for use as probiotics in C. gariepinus farming.