Isolation and Characterization of Probiotic Lactic Acid Bacteria from African Catfish (Clarias gariepinus) and Nile Tilapia (Oreochromis niloticus) for African Catfish Aquaculture Production

Abstract

African catfish (Clarias gariepinus) is one of the most commercially important fish species in Ethiopia known for its nutritional richness. However, it is usually affected by pathogens. The objective of this study was to evaluate the probiotic lactic acid bacteria isolated from African Catfish and Nile Tilapia for African Catfish aquaculture production. The study was conducted in Jimma city. A cross-sectional study design was employed. A total of 14 fish samples (7 each of African catfish and Nile tilapia) were collected from Jimma city, Boye River, and a purposive sampling technique was employed. Evaluation of probiotic properties of lactic acid bacteria, detection of pathogens from aquarium, surface, and gut of fish, and application of probiotics in larvae of African catfish was conducted following the standard procedures. Data were analyzed using SPSS software version 20.0. A total of 80 LAB isolates were obtained among which Lactobacillus spp were the dominant (91.25%) followed by Lactococcus (7.5%). From a total of 80 isolates of LAB, 64 (80%), and 48(60%) tolerated pH3 and pH2, respectively. On the other hand, all 80 (100%) of the isolates survived 0.3% bile salt while 75 (93.75%) survived 0.5% bile salts. A total of 43 isolates of LAB, which tolerated the pH2 and 0.5% bile salt, the highest antimicrobial activity (≥ 15mm diameter of zone of inhibition) in all pathogens was exhibited by isolates coded AFG8, AFG10, NTG8, and JUT89. Moreover, from 43 isolates, 17 (39.53%) showed antimicrobial activity against 4 to 5 pathogens. On the other hand, the majority of LAB isolates were susceptible to chloramphenicol and erythromycin (64.7% each) followed by clindamycin (52.9%). However, all isolates were highly resistant (100%) to penicillin G, streptomycin, ciprofloxacin, and kanamycin. Overall, 60.71% of fish samples were positive for S. aureus, and 32.14% for Salmonella spp. In both surface and gut of African catfish and Nile tilapia, Listeria, Shigella, Pseudomonas spp, and E. coli were not detected. All isolates of S. aureus isolated from the guts of African catfish and Nile tilapia were susceptible to ciprofloxacin, chloramphenicol, and erythromycin. Furthermore, all Salmonella spp isolated from the gut of African catfish were also susceptible to kanamycin, ciprofloxacin, and streptomycin. The pre and post-assessment of pathogens in an aquarium during application of probiotics showed that all aquaria had initially E. coli, Listeria spp, Salmonella spp, and Pseudomonas spp. After probiotics LAB were applied, an aquarium that had probiotic Lactobacillus spp (coded AFG10 and AFG8) inhibited all pathogens. Moreover, the aquarium which had Lactococcus spp NTG8, inhibited all pathogens except E. coli whereas Lactobacillus spp (coded JUT89) inhibited only Salmonella spp. The application of probiotics enhanced the weight and length of Africa catfish with the highest fish growth performance recorded in an aquarium that had AFG10 and AFG8, with slightly higher values for AFG10. In contrast, the least growth values were observed in the aquarium that had JUT89 followed by the control. The variation in the final mean weight between the control and the treatment groups is statistically significant (P=0.02). Generally, both fishes are good sources of probiotic lactic acid bacteria. The probiotics isolated from African catfish enhanced the growth performance of African catfish than Nile tilapia. and Tej. Besides optimization of the growth condition of probiotics isolated from African catfish for its better growth performance, a comprehensive evaluation of other sources of probiotics for wider application in the growth enhancement of Nile tilapia was recommended.