水産養殖研究開発ジャーナル

概要

Aeromonas Spp. Infection in Farmed Nile Tilapia, Oreochromis Niloticus

Kassaye Balkew Workagegn1*, Bekele Lema2 , P. Natarajan1 , L. Prabadevi2

Nile tilapia is one of the major formed fish species worldwide. However, pathogenic bacteria such as Aeromonas spp. cause a high economic losses. Therefore, the present study was aimed at isolating and investigating the effects of Aeromonas spp on Nile tilapia and evaluating its pathogenicity change after experimental infection. For this purpose, naturally infected Nile tilapia collected form the Ambo University experimental fishpond were transported to the biology laboratory using aseptic plastic bags. Aeromonas spp. isolation and identification were made using morphological and biochemical characterizations. The pathogenicity test was carried out for Aeromonas spp using an intra-peritoneum injection along the caudal peduncle of the fish. Finally, sensitivity test of the isolate was performed using different antibiotics. The results showed that after 24 hours of artificial injections, all the fish decreased their feeding rate and exhibited erratic swimming behaviour. The fish also remained at the bottom and became darkened on their dorsal body part. The fish also showed high hyperaemia on the base of the fins, fin rot and erosion, Internally, they showed pale gills, high intestinal fluid accumulation, pale gonads, pale liver and enlarged gall bladder. The fish also showed an increased of white blood cells as they may migration from the spleen to the blood circulation system. The results also showed that the Aeromonas isolate was highly sensitive to erythromycin and tetracycline. In conclusion, the Aeromonas isolate exhibited a serious effects on external and internal organs of Nile tilapia reared under pond culture system. Additionally, the isolate might affect the immune system of the fish by influencing the nature of blood cells. As control mechanism of the isolate, erythromycin, and tetracycline were more effective and thus these antibiotics can be used for treating the isolate by mixing with fish feed. However, as antibiotics have cumulative effect, it is important to find an alternative controlling methods such as plant based antibiotics and improve production management of the aquaculture systems.