Description of a presumptive hepatopancreatic reovirus, and a putative gill parvovirus, in the freshwater crayfish Cherax quadricarinatus

The redclaw freshwater crayfish Cherax quadricarinatus has a reputation for being hardy and resistant to handling stress. However, in recent years, po ssibly since 1996, C. quadricarinatus farmers in northern Queensland have n oted a decrease in stress resistance in their stock. A presumptive reovirus in the hepatopancreas; and a putative parvovirus in the gills, were associ ated with chronic mortalities in C. quadricarinatus at one northern Queensl and farm. Hypertrophic nuclei with marginated chromatin were observed in gi ll epithelium in moribund crayfish which had recently been relocated to a l aboratory from the holding tank facility on the farm. Affected nuclei appea red to be vacant or contained a faint granular basophilia in H&E stained se ctions. However, toluidine blue staining revealed a homogenously granular a ppearance of the nuclei. Transmission electron microscopy revealed approxim ately 20 nm diameter virus-like particles within the nucleus. Eosinophilic, Feulgen-negative, cytoplasmic inclusions were observed in distal hepatopan creatocytes in 1 moribund C. quadricarinatus collected from the same on-far m holding tank approximately 6 mo later. This crayfish did not display the gill lesions. Transmission electron microscopy showed that the inclusions c ontained icosahedral virus particles 35 to 40 nm in diameter. The histopath ology and preliminary virus morphology of the presumptive hepatopancreatic reovirus, and the histopathology, ultrastructural pathology and preliminary virus morphology of the putative gill parvovirus, are reported herein.