Retention of infectious haematopoietic necrosis virus infectivity in fish tissue homogenates and fluids stored at three temperatures.
Pools of brain, kidney, spleen, liver and gut tissues from several rainbow trout, Salmo gairdneri Richardson, and whole sockeye salmon, Oncorhynchus nerka (Walbaum), fry were homogenized with a known amount of infectious haematopoietic necrosis virus (IHNV). Virus was also added to ovarian fluids and sera pooled from several rainbow trout. The plaque assay was used to determine the retention of IHNV infectivity after different storage periods at 20°C, 4°C and —20°C. The work was used to evaluate homogenization as a remote field treatment of IHNV samples before shipment to the laboratory. Maintenance of viral infectivity varied widely among different homogenates and fluids. For short-term storage, 4°C was generally the most efficient temperature for preserving infectious virus in ovarian fluids, Sera and homogenates of eggs, spleen, whole fry and brain, while infectivity was most efficiently preserved in kidney and liver homogenates by storage at −20°C. Infectious virus was not detected in any sample stored for one year at −20°C. Variations in retention of viral infectivity make homogenization of samples in the field followed by transfer to the laboratory unacceptable.