Effects of experimentally induced infections of goldfish Carassius auratus with cyprinid herpesvirus 2 (CyHV-2) at various water temperatures

In this study, we examined the influence of water temperature on the development of herpesviral haematopoietic necrosis (HVHN) in goldfish Carassius auratus after experimentally induced infection with cyprinid herpesvirus 2 (CyHV-2). In Expt 1, Ryukin goldfish were infected with CyHV-2 by intraperitoneal injection and maintained at 4 different water temperatures. Cumulative mortalities of the 15, 20, 25 and 30 degrees C groups were 10, 90, 90 and 60%, respectively. Therefore, the temperature range of 20-25 degrees C is considered highly permissive for HVHN. One of 6 surviving fish of the 15 degrees C group died after a rapid temperature increase to 25 degrees C at 30 d post infection. All 3 Edonishiki goldfish, co-reared with the surviving Ryukin in tanks where the water temperature was increased from 15 to 25 degrees C, died. In Expt 2, Edonishiki goldfish were exposed to CyHV-2 by bath immersion at 13 or 24 degrees C, resulting in cumulative mortalities of 0 and 87%, respectively, at 28 d post-exposure. No mortality of the surviving Edonishiki in the 13 degrees C treatment was observed when the water temperature was increased to 24 degrees C. In addition, in Expt 2, no mortality was observed in any Ranchu co-reared with CyHV-2-immersed Edonishiki in the group where water temperature was increased from 13 to 24 degrees C, even after re-immersion challenge with CyHV-2. It is interesting to note that CyHV-2 DNA was detected in the kidneys of 4 of the 5 surviving Ranchu co-reared with the CyHV-2-immersed Edonishiki group where the water temperature was increased from 13 to 24 degrees C. Therefore, it is likely that the surviving Edonishiki of the 13 degrees C group were virus carriers. This study indicates that most fish infected with CyHV-2 at 13-15 degrees C acquire resistance to HVHN, but as carriers they are able to infect naive fish.