Tilapia tilapinevirus, also known as tilapia lake virus (TiLV), is an emerging fish virus that primarily affects tilapines. However, the virus has also been detected in a few non-tilapines. As tilapia is generally farmed in polyculture systems along with carps in South Asian countries, there is a likelihood that TiLV-infected tilapia can transmit the virus to the co-cultured species. In view of the above, the susceptibility of three carp species, namely catla (Catla catla), mrigal (Cirrhinus mrigala) and silver carp (Hypophthalmichthys molitrix) was evaluated vis-à-vis tilapia, following experimental infection with TiLV. No clinical signs and histopathological alterations could be observed in carps. RT-qPCR revealed that TiLV copy numbers in liver and brain of all the three carps were almost negligible and did not show any increase with time, suggesting that the virus did not replicate in liver and brain, the target organs of TiLV. Further, TiLV could not be isolated from pooled liver and brain tissues of carps using permissive CFF cell line. On the contrary, in tilapia, typical clinical signs and histopathological lesions were observed and there was significant increase in TiLV copy number up to 6 days post-injection. Furthermore, the virus was successfully isolated from pooled liver and brain tissue of infected tilapia. From the above findings, it could be concluded that C. catla, C. mrigala and H. molitrix are resistant to TiLV infection and unlikely to be carriers for this virus.

Infection with Aphanomyces invadans is a serious disease affecting freshwater and brackishwater fish. Even after 50 years of its first occurrence, to date, there is no effective treatment for this disease. To develop an effective treatment against this disease, in the current study, we have evaluated the potential of six commonly used chemicals and drugs with known antifungal properties against different life-stages (zoospore production, germination of zoospores and growth of hyphae) of A. invadans. The chemicals namely formalin, potassium permanganate (KMnO4), hydrogen peroxide (H2O2), sodium thiosulphate (Na2S2O3) and drugs including amphotericin B and fluconazole were evaluated in a dose-dependent manner (0.1, 1.0, 5, 10 and 100 ppm) under in vitro conditions. Out of the chemicals tested, formalin could completely inhibit zoospore production and significantly inhibit germination of zoospores and growth of hyphae at 10 ppm, however, complete inhibition of zoospore germination and growth of hyphae could only be observed at 100 ppm. In the case of H2O2, there was significant inhibition of germination of zoospores and growth of hyphae at the highest concentration of 100 ppm, but it could not completely inhibit zoospore production, germination of zoospores and growth of hyphae. KMnO4 at the highest tested concentration (100 ppm), completely inhibited zoospore production and significantly inhibited germination of zoospores and growth of hyphae. Na2S2O3 was found to be ineffective against all the three life-stages of A. invadans even at the highest tested concentration of 100 ppm. Out of the two antifungal drugs, fluconazole could reduce the germination of zoospores and growth of hyphae significantly at a dose of 1 ppm. On the other hand, in the case of amphotericin B, significant inhibition of germination of zoospores and growth of hypahe was observed only at 100 ppm. Both drugs completely inhibited zoospore production only at 100 ppm. From the findings of the present study, it can be inferred that out of the six compounds, formalin and fluconazole have better anti-oomycete effects under in vitro conditions. The information generated would serve as a basis for developing treatment measures against infection with A. invadans in aquaculture ponds.