Occurences And Antimicrobial Sensitivity Of Bacteria In Rufiji Tilapia And Its Hybrids With Nile Tilapia Fingerlings At Different Salinity Levels

ABSTRACT

Diseases at hatchery stage are among challenges that hinder optimal mariculture development in Tanzania. Information on the occurrences of bacterial infections in mariculture hatchery in the country is limited. Thus, this study was conducted to determine the occurrence and antibacterial sensitivity of bacteria species in Rufiji tilapia and hybrids fingerlings of Nile tilapia female crossbreed with Rufiji tilapia male farmed at different salinity at Institute of Marine Science (IMS) - Mariculture Center in Pangani-Tanga. A total of 120 fingerlings (2.07-3.49g for Rufiji tilapia (RF), 6.61- 6.98g for hybrids (HB) and 250ml water samples were collected from three replicated tanks of about 30 m2 set at water salinity level of 2, 15, 25 and 35. Bacterial loads were determined as CFU ml-1. Isolated bacteria were identified to genus or species level. Molecular identification was done for Staphylococcus and Bacillus spp. Antibiotic sensitivity test was conducted using the following antibiotics; Tetracycline (TE30), Chloramphenicol (C30), Gentamycine (CN10), Amoxycilin (AMC30), Neomycine (N10), Ciproflaxcine (CIP5), Cefataxime(CTX30), Sulfamethoxazole (SMX50), Ampicillin (AMP10), Erythromycine (E15)and Penicillin G(P10). Bacterial loads (log10 CFUml-1) ranged from 6.34±0.12- 4.79±0.94 in HB; 5.99±0.70-4.44±0.45 in RF; 6.42±0.44-5.07±0.53 in Water with HB and 5.62±0.53-4.28±0.16 in Water with RF. There were no significant differences in bacterial loads between fish species at all levels of water salinity (p>0.05). A total of four genera were isolated namely; Staphylococcus, Escherichia, Micrococcus and Bacillus. Confirmation by PCR of 56 isolates showed; 69.4% positive for Staphylococcus spp, 5.6% S. aureus, 17 % S. epidermidis, 21.4% Bacillus cereus and 7.1% B. subtilis. Antimicrobial sensitivity test indicated that isolates were highly sensitive to Ciprofloxacin (100%) and Tetracycline (86.7%), and were

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resistant to Sulfamethoxazole and Penicillin. Presence of bacteria species of which some are potentially pathogenic to fish may cause diseases and mortalities to fingerlings hindering mariculture development in the country. Biosecurity measures should be employed to reduce chances of bacterial contamination at hatchery.