EFFECTS OF SELECTED PROBIOTICS ON THE GROWTH PERFORMANCE, IMMUNE MODULATION AND HISTOPATHOLOGY OF AFRICAN CATFISH (CLARIAS GARIEPINUS)

Abstract

This study was carried out to determine the effects of probiotics Gram-negative, Pseudomonas fluorescens and Gram-positive, Bacilus subtilis on the growth performance, histology examination and immune modulation of African Catfish, Clarias gariepinus challenged with Clostridium botulinum. This study involved two experiments carried out in two phases (Pseudomonas flourescens on C. gariepinus and Bacillus subtilis on C. gariepinus). P. fluorescens, B. subtilis and C. botulinum isolates were removed from the gut, gill and skin organs of procured adult samples of Clarias gariepinus from three different commercial fish farms in Akure, Ondo State, Nigeria. Biochemical tests were performed on the bacterial isolates using standard microbiological techniques for their identification. The experimental diets were prepared at different probiotics bacterial concentration comprises of five treatments of different bacterial suspension, including the control (T1), T2(103), T3 (105), T4(107) and T5(109). Three replicates for each treatment type were prepared. Growth performance and nutrients utilization indices were calculated. The proximate analysis of fish carcass and experimental diet was carried out using standard methods. After feeding for 70 days, Haematological values and Histological test were done following standard methods, also a subgroup from each experimental treatment was challenged by inoculating Intraperitonieally (I/P) with different concentration of pathogenic C. botulinum The physical and biochemical characteristics of bacterial isolates were confirmed to be P. fluorescens and C. botulinum. Antibacterial activity tests showed inhibition zone with mean value of 3.7 mm which indicates high level of antagonism. Statistically, there were significant differences (P< 0.05) in the growth performance and nutrient utilisation of C. gariepinus. Best weight gain and feed conversion ratio were recorded in fish fed T4 (107) and poorest value obtained in the control. Haematological analyses of C. gariepinus fed the experimental diets indicated that all the fish fed diets with P. fluorescens had marked significantly (p<0.05) higher White Blood Cell than the control diet. The results of the challenge test showed that fish fed the control diet had the highest mortality rate. Histological examination of the gill, intestine and liver of fish in this study showed several histopathological alterations in fish fed the control diets compared with those fed the P. fluorescens diets. The physical and biochemical characteristics of bacterial isolates confirmed to be Bacillus subtilis and Costridium butilinum. Antibacterial activity tests showed inhibition zone with mean value of 4 mm which indicates high level of antagonism. There was no significant difference (P>0.05) in the initial weight of the fish at the beginning of the experiment. Statistically, there were significant differences (P< 0.05) in the growth performance and nutrient utilisation of C. gariepinus at the end of the experiment. Best weight gain and FCR were recorded in fish fed T2(103) and poorest value obtained in the control. Haematological analyses of C. gariepinus fed the experimental diets indicated that all the fish fed diets with B. subtilis had marked significantly (p<0.05) higher White Blood Cell than the control diet. The results of the challenge test showed that fish fed the control diet had the highest mortality rate. The study indicated that the optimum level of P. fluorescens required for C. gariepinus growth and white blood cells formation is 107 CFU g-1 and carcass protein deposition is 105 CFU g-1 while B. subtilis requires for C. gariepinus growth, white blood cells formation and carcass protein deposition is 103 CFU g-1. It also confirmed both bacteria (P. fluorescens and B. subtilis) as efficient probiotics that are capable of improving the immune response of C. gariepinus against the attack of a virulent fish pathogen, C. botulinum.