Effects of Dietary Pseudomonas fluorescens Supplementation on Growth Performance and Immune Response of African Catfish (Clarias gariepinus) Juveniles Challenged with Clostridium botulinum

Abstract

A 70-day feeding trial was conducted to evaluate the effects of dietary Pseudomonas fluorescens supplementation on the growth performance and immune response of Clarias gariepinus juveniles. Five diets containing graded probiotic inclusion levels (T1, control; T2, 10^3 cfu g−1; T3, 10^5 cfu g−1; T4, 10^7 cfu g−1; T5, 10^9 cfu g−1) were fed to fish in triplicate tanks (15 fish per tank). After the feeding period, subgroups were challenged intraperitoneally with C. botulinum (0.2 ml of 10^7 cells ml−1) and observed for 10 days. P. fluorescens. was confirmed by morphological and biochemical tests and shown to produce in vitro antagonism against C. botulinum (mean inhibition zone ≈ 3.7 mm). Fish fed probiotic diets showed significantly (p < 0.05) higher final weight, weight gain, specific growth rate (SGR), feed efficiency (FER) and lower feed conversion ratio (FCR) than controls; the best performance occurred at 10^7 cfu g−1. Haematological indices showed elevated total white blood cell (WBC) counts in probiotic-fed fish, with the highest WBC at 10^7 cfu g−1. Following challenge, survival was highest in T4 (≈80%) and lowest in control (0%). Histopathology of gill, intestine and liver revealed fewer lesions in probiotic-fed fish. Results indicate that dietary P. fluorescens at 10^7 cfu g−1 improves growth and non-specific immune parameters and increases resistance of C. gariepinus to C. botulinum under experimental conditions.