Susceptibility of stone loach (Barbatula barbatula) and hybrids between sterlet (Acipenser ruthenus) and beluga (Huso huso) to cyprinid herpesvirus 3

Cyprinid herpesvirus 3 also known as koi herpesvirus is a causative agent of highly contagious disease (koi herpesvirus disease) and can cause significant losses in fish stocks. The disease is restricted to koi and common carp, but recent investigations have shown that other cyprinids as well as non-cyprinid species are asymptomatically susceptible to this virus and can play either a role as a potential carrier or can contribute to biological conservation of this virus. The susceptibility of two non-target species, stone loach (Barbatula barbatula) and sterbel – a hybrid between sterlet (Acipenser ruthenus) and beluga (Huso huso) to cyprinid herpesvirus 3 was tested by means of their co-habitation together with naïve koi and intraperitoneally KHV-infected koi (primary challenge). On the 15 th day post-infection (dpi), a secondary challenge was started (a portion of the surviving stone loach and sterbel were transferred to tanks with other naïve koi). All dead as well as surviving fish were investigated for the presence of KHV DNA in pooled samples of tissue from individual fish by nested PCR. Sampling for PCR from surviving fish was performed on the 15th dpi and on the 30th dpi of the primary challenge, and on the 30th dpi of the secondary challenge. During the primary challenge (up to the 30th dpi), average cumulative mortality in duplicated experimental groups was as follows: koi 100%, sterbel and stone loach both 5%. In the primary challenge, no surviving stone loach or sterbel sampled on the 15th dpi or those that died previously were found to be positive for viral DNA. Results of PCR revealed the presence of KHV DNA in 95% of co-habited naïve koi samples. PCR analysis of tissues taken from surviving fish on the 30th dpi revealed the presence of viral DNA in 77.8% (7/9) of stone loach and in 22.2% (2/9) of sterbel. Cumulative mortality of fish in the secondary challenge was 100% for stone loach and for koi co-habitating with them, and 50% for koi co-habitating with sterbel, which all survived. Despite the high mortality of koi and stone loach in the secondary challenge (probably caused by malfunction of biofilters or bacterial infection), none of them, nor any of the sturgeon hybrids were considered to be positive for KHV DNA. In summary, the hybrid between sterlet and beluga and the stone loach seemed to be susceptible to cyprinid herpesvirus 3, but we could not prove that they can transfer this virus to naïve koi.