PREVALENCE OF TILAPIA LAKE VIRUS (TILV) IN FARMED AND WILD FISHES OF NORTH TAMIL NADU, INDIA

India offers a huge potential for aquaculture development and viral diseases are the major factor for serious economic impediments. Outbreaks of tilapia lake virus (TiLV) in commercial tilapia farming have been reported in many countries, viz., Ecuador, Israel, Colombia, Egypt, Thailand, China, Malaysia and India. TiLV infection has been reported in various farmed tilapia species, viz., hybrid tilapia, Nile tilapia, red tilapia and wild species of tilapia. Currently, no clinical infection of TiLV has been reported in fish species other than Tilapia. This study was carried out with an objective to screen the prevalence of TiLV in various species of fishes including tilapia in the districts of North Tamil Nadu, India.

A total number of 104 fish samples which included various species of fishes (Table.1) were collected from the fish farms, lakes and ponds of northern districts in Tamil Nadu (Chennai, Tiruvallur, Salem, Cuddalore, Krishnagiri, Chengalpattu, Vellore, Erode and  Pondicherry) during September 2017 to December 2018. Tissue samples of muscle, eye, brain, gill, intestine, liver and kidney from fishes were screened for TiLV by Semi nested RT-PCR,  sequenced and compared with the GenBank database of the NCBI (http://blast.ncbi.nlm.nih.gov) submitted to NCBI GenBank and phylogenetic analysis was carried out.

The results of the PCR screening for TiLV showed that Nile and red tilapia of Krishnagiri district, wild tilapia of Vellore district were positive for TiLV in the first step indicating heavy infection (Figure.1), Whereas, tilapia samples collected from  other districts showed second step positive. Among the fishes other than tilapia screened  freshwater eel showed second step positive for TiLV.Among the total no. of 104 fish samples screened, 41 fish samples were found to be positive for PCR by TiLV with a prevalence of 39.4%. Phylogenetic analyses showed that TiLV strain of Tamil Nadu (MG515169 & MG515170) is very closely related to TiLV strain of Israel (KU751816) with high DNA The results of this study a) confirmed the presence of TiLV in Tilapia sp. in Tamil Nadu b) the presence of TiLV in the wild fish like Anguilla sp. (eel) shows that the wild fishes which share the habitat with Tilapia act as carriers of the disease