Aquaculture and Fishery Management

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    BACTERIAL PATHOGENS OF NILE TILAPIA FISH, Oreochromis niloticus (LINNAEUS, 1758) WITH SPECIAL REFERENCE TO Aeromonas hydrophila IN LAKE HAWASSA, ETHIOPIA AND MODULATION OF INFECTION USING DIEATERY SUPPLIMENTATION WITH GINGER (Zingiber Officinale)
    (HAWASSA UNIVERSITY, 2024-03) ALAZAR ERGENA KESHAMO
    Fish is one of the known aquatic animals which serve as food for human beings. However, fish are constantly exposed to diseases and usually succumb to infections after being exposed to stress. Environmental factors such as variations in the physico-chemical parameters of water act as stressors and can predispose fish to diseases. This study was thus undertaken to evaluate the physico-chemical and bacteriological quality of Lake Hawassa, characteriz bacterial pathogens with emphasis on Aeromonas hydrophila of Oreochromis niloticus, and asses the effect of Ginger (Zingiber officinale) powder on Aeromonas hydrophila infection. Seventy-two water samples and 360 fish samples were collected from Lake Hawassa for 12 months from January 2021 to December 2021. The physico-chemical and bacteriological quality of the water, isolation, characterization and identification of bacterial pathogens of fish and, haematological parameters of fish were assesed following standard procedures. To test the pathogenicity of Aeromonas hydrophila and their effects on haematology of fish, 270 fish were collected from the ponds located at Hawassa University and transported to the laboratory and fed a basal diet. After two weeks of acclimatization, the fish were divided into one control and eight treatments each in triplicaten and injected with different concentrations of Aeromonas hydrophila (1 x 101 to 1 x 108 CFU/ml). To determine the effect of Ginger powder on the haematology of Oreochromis niloticus and Aeromonas hydrophila infection 300 fish were collected from the Fish ponds located in Hawassa University and transported to laboratory and fed a basal diet during two weeks of acclimatization. The fish were distributed into one control and four treatment groups and fed with different concentrations of Ginger powder (0.00, 1, 3, 5, 8 and 12 g ginger/kg) for eight weeks. At the end of eight weeks, the fish were injected with 0.2ml of Aeromonas hydrophila at the concentration of 1 x 107 CFU/ml. Blood samples were collected from the fish before and after the Aeromonas hydrophila injection. The study showed a significant variation in water quality parameters xviii among sites and seasons (P < 0.05). Seventy-two point seven percent (72.7%) of physico- chemical parameters of Lake Hawassa were not found with in the critical limits for aquatic life, particularly fish. The study also indicated high bacterial loads in water samples of the lake. Sixty-four percent (64%) prevalence of bacterial infection was recorded for fish in the lake. The prevalence of infection in female fish was higher than in male fish. The highest prevalence was recorded within the smaller fish group (12-18 cm) than the larger ones (24-29 cm). Significantlly high bacterial loads were recorded from the intesitine of fish during the summer (wet) season (P < 0.05). Bacterial isolates such as Aeromonas hydrophila, Escherichia coli, Edwardissela tarda, Vibrio, Bacillus, Staphylococcus, Salmonella, Flavobacterium, Pseudomonas and Shigella species were isolated from Oreochromis niloticus of Lake Hawassa. A prevalence of 17.7% of Aeromonas hydrophila was recorded in Nile tilapia. All Aeromonas isolates were 100% resistance to amoxicillin, ampicillin and penicillin. The majority of Aeromonas isolates showed multiple antibiotic resistances. The value of red blood cells (RBCs), haemoglobin (Hb) and haematocrit (Hct) was significantly decreased (P < 0.05) in the blood of Oreochromis niloticus collected from more polluted sites of the lake compared to relatively less polluted site. In contrast, erytrocyte sedimentation rate (ESR) and white blood cells (WBCs) count showed significant (P < 0.05) elevation for more polluted sites than less polluted site. RBCs count, Hb, Hct and WBCs count showed a significant rising trend in their values with increasing size of the fish (P < 0.05). The male fish have significantly higher concentrations of haematological parameters, such as RBCs, Hb and Hct than the females (P < 0.01). Haematological parameters of infected fish were significantly different from control fish (P < 0.01). The haematological parameters of the fish such as RBC, Hct, Hb, MCH, MCHC and WBC were significantly increased to all concentrations of the Ginger powder-supplemented diet when compared to fish fed the control diet. There was no mortality of Oreochromis niloticus before injection xix with Aeromonas hydrophila. Mortality in experimental fish was observed after 3 days of the bacterial challenge. The highest mortality rate (70%) was recorded for the control group followed by the 3 g/kg and 12 g/kg Ginger powder-supplemented diet. Supplementation of Ginger powder at the concentration of 5 g/kg diet provided better protection to Oreochromis niloticus against Aeromonas hydrophila infection. There is an urgent need for continuous monitoring of Lake Hawassa to detect changes in the water quality. The recovery of potentially pathogenic bacteria of humans, in the fish, suggests that if the fish are improperly handled, undercooked, or consumed raw may cause diseases in susceptible consumers. The use of 5 g/kg dietary Ginger powder diet is recommended for the control of Aeromonas hydrophila infection in Nile tilapia, Oreochromis niloticus.