Susceptibility of cultivable species to tilapia lake virus (TiLV) and effect of withania somnifera (Ashwagandha) against TiLV

Tilapia lake virus (TiLV) disease is an emerging threat to the aquaculture farmers as it is contagious and results in high mortality of fishes. Since tilapia is important to domestic and global food security providing a major protein rich food source and livelihood, the massive die-offs are affecting the entire aquaculture economy. Till date, no cure for TiLV is reported. We have introduced a medicinal plant Withania somnifera to act against TiLV. The present study investigates the effect of oxidative stress on infected tilapia and its amelioration with the aqueous extract of Withania somnifera root (WSE). The mortality was successfully reduced in both laboratory and field trials on treatment with WSE. The oxidative stress and hematological parameters of TiLV infected fishes were found to be adversely affected. Application of WSE caused a significant improvement in these parameters. In the field, its application successfully controlled themortality.
Till date, no clinical infection of TiLV in other fishes has been reported in India. To confirm the field reports obtained from the different farms of Kerala, co- infection studies in the laboratory and tests of the field samples suggest that fry and fingerlings of Catla (Catla catla), Rohu (Labeo rohita) and Jayanti Rohu are susceptible to TiLV infection. The affected fish exhibited skin erosion, loss of scales, exophthalmia and abnormal swimming pattern. Histological lesions like syncytial formation and lymphocytic and RBC infiltration can be observed in the liver of infected Jayanti rohu, similar to the changes observed in tilapia.
Co-infection studies indicate that TiLV can be horizontally transmitted and can infect other fresh water fishes. Overall results proved that WSE can be considered as an effective treatment against TiLV mortality. Fresh water fishes like catla, rohu and jayanti rohu in their fry and fingerling stages are susceptible to TiLV infection. This is the first report on an effective treatment for TiLV and new susceptible species of TiLV.