Saprolegniaceae Infection in white clawed crayfish (Austropotamobius pallipes complex) in an experimental hatchery in northern Italy

The white-clawed crayfish Austropotamobius pallipes complex, is a protected European native species as it is considered endangered organism. In order to preserve this crustacean carefully planned restocking programs with production of the juveniles in captivity are essential. An episode of mortality occurred during an intensive crayfish breeding trial from autumn 2004 to autumn 2005 in a North-eastern Italy experimental trout breeding. In October 2004, 32 crayfish (15 males and 17 females) captured in Ardo river were housed inside the hatchery, initially in a concrete tank, then were moved to a fibreglass tank, where mating took place. In the spring 2005, 11 barred female were transferred in a Californian tank for the incubation of the eggs. In June 2005 all the crayfish in the fiberglass tank died in presence of low hygienic conditions,. In August, after the hatching of the eggs, the females were placed in a fiberglass tank like to the previous where a total mortality occurred after two weeks. On the whole twenty-three crayfishes were submitted at microscopical, mycological, bacteriological and histological investigations. Saprolegniaceae were isolated from gills, legs and abdomen in all the samples, while Fusarium sp. in only one specimen. At the histology coenocytic branched fungal hyphae were observed in the gonopods, abdominal exoskeletons, eye stalks and in the joint of the legs, with heavy inflammatory lesions and necrosis in the hypoderm. The skeletal muscle and green gland were sometimes colonized; in some cases the hyphae were surrounded by melanin. The mortality was related to Saprolegniaceae infection, induced by food remnants.