Establishment and characterization of fantail goldfish fin (FtGF) cell line from goldfish, Carassius auratus for in vitro propagation of Cyprinid herpes virus-2 (CyHV-2).

Background: Herpesviral hematopoietic necrosis disease, caused by cyprinid herpesvirus-2 (CyHV-2), is responsible for massive mortalities in the aquaculture of goldfish, Carassius auratus . Permissive cell lines for the isolation and propagation of CyHV-2 have been established from various goldfish tissues by sacrificing the fish. Here, we report the development of a cell line, FtGF (Fantail Goldfish Fin), from caudal fin of goldfish using non-lethal sampling. We also describe a simple protocol for successful establishment and characterization of a permissive cell line through explant method and continuous propagation of CyHV-2 with high viral titer using this cell line.
Methods: Caudal fin tissue samples were collected from goldfish without killing the fish. Cell culture of goldfish caudal fin cells was carried out using Leibovitz's L-15 (L-15) medium containing 20% FBS and 1X concentration of antibiotic antimycotic solution, incubated at 28 °C. Cells were characterized and origin of the cells was confirmed by sequencing fragments of the 16S rRNA and COI genes. CyHV-2 was grown in the FtGF cells and passaged continuously 20 times. The infectivity of the CyHV-2 isolated using FtGF cells was confirmed by experimental infection of naïve goldfish.
Results: The cell line has been passaged up to 56 times in L-15 with 10% FBS. Karyotyping of FtGF cells at 30 ^th, 40 ^th and 56 ^th passage indicated that modal chromosome number was 2n = 104. Species authentication of FtGF was performed by sequencing of the 16S rRNA and COI genes. The cell line was used for continuous propagation of CyHV-2 over 20 passages with high viral titer of 10 ^7.8±0.26 TCID ₅₀ /mL. Following inoculation of CyHV-2 positive tissue homogenate, FtGF cells showed cytopathic effect by 2 ^nd day post-inoculation (dpi) and complete destruction of cells was observed by the 10 ^th dpi. An experimental infection of naïve goldfish using supernatant from infected FtGF cells caused 100% mortality and CyHV-2 infection in the challenged fish was confirmed by the amplification of DNA polymerase gene, histopathology and transmission electron microscopy. These findings provide confirmation that the FtGF cell line is highly permissive to the propagation of CyHV-2.
Competing Interests: The authors declare that they have no competing interests.
(© 2020 Dharmaratnam et al.)