Susceptibility of selected tropical non-tilapine ornamental cichlids to Tilapia tilapinevirus following experimental infection

The emergence and spread of transboundary aquatic animal diseases have been frequently associated with in-ternational trade of live aquatic animals. Tilapia is one of the most traded aquatic animals and the recent global spread of Tilapia tilapinevirus, also known as tilapia lake virus (TiLV), is speculated to be due to transboundary movement of infected fish. Further, extensive trade of ornamental cichlids can be a major threat to the spread of TiLV. However, there is little information about susceptibility of ornamental fishes, especially cichlids, to this virus. In this background, the present study evaluated the susceptibility of three ornamental cichlids (angelfish, firemouth cichlid and parrotfish) and two non-cichlids (three spot gourami and goldfish) vis-`a-vis Nile tilapia following experimental infection with TiLV through intraperitoneal injection. The study carried out quantifi-cation of viral load using real-time PCR, histopathology and isolation of the virus in permissive cell line developed previously from Oreochromis niloticus heart (OnH). Experimental infection resulted in the successful reproduction of the disease in tilapia with typical clinical signs. In angelfish, 40% mortality was observed and the TiLV copy number/100 ng RNA was determined to be 2.49 x 106, 1.52 x 106 and 2.64 x 104 in the target tissues, namely liver, spleen and brain, respectively at 4 days post-infection (dpi). In addition, TiLV could be detected in the target tissues till end of the experimental period of 24 days. Although no clinical signs or mortality were observed in firemouth cichlid, but TiLV copies were detected in the target organs with significant increase in the viral load up to 12 dpi. Histopathological examination of liver tissue of the experimentally infected fishes revealed typical syncytial cells only in tilapia whereas necrosis of hepatocytes was observed in tilapia, angelfish and firemouth cichlid. Besides, TiLV could be isolated from target tissues of both angelfish and firemouth cichlid at 8 dpi, using OnH cell line. On the other hand, in parrotfish, three spot gourami and goldfish, the virus copy number in the target tissues showed a decline from 1 dpi and no evidence of virus replication could be noticed in the cell line studies. Hence, these three ornamental fishes were considered resistant to experimental infection with TiLV. The findings of this study indicated the existence of wide host-range of TiLV in non-tilapine orna-mental fishes including angelfish and firemouth cichlid, and the potential role of these fishes in the epidemiology of TiLV disease.

Automated summary

The international trade of live aquatic animals has led to the emergence and spread of transboundary aquatic animal diseases, including the recently global spread of TiLV. This study evaluated the susceptibility of various ornamental fishes to TiLV and found that angelfish and firemouth cichlid were susceptible, while three spot gourami, parrotfish, and goldfish showed resistance. These findings highlight the potential role of non-tilapine ornamental fishes in the epidemiology of TiLV.