An epidemic of hepatopancreatic necrosis disease (HPND) with a high mortality rate (40%-50%) recently occurred in the cultured Chinese mitten crab, Eriocheir sinensis, which is a very important economic crustacean species in China. Histology revealed infection by a microsporidian parasite within the cytoplasm of the epithelial cells of the hepatopancreas. Numerous discrete inclusions in the infected cells and presumably free parasite spores were also observed. By negative staining using electron microscopy, a typical morphology of spores was observed with a protuberant front of the anchoring disc. Infection was confined to the epithelial cells of the hepatopancreas, with no other organ implicated. By sequencing the PCR products using specific primers based on conserved regions of microsporidian small subunit (18S) ribosomal DNA, it was revealed that the parasite from HPND ponds had 99% sequence identity to that of Hepatospora eriocheir. Phylogentic analysis also placed the microsporidian in the same lineage as H. eriocheir. This study reported the first case of widespread infections of H. eriocheir associated with HPND found in the pond-reared Chinese mitten crab, E. sinensis. The description of microsporidian in this important commercial host is fundamental for future consideration of factors affecting stock health and sustainability.

An eight-week study was conducted to determine requirements for chicory polysaccharides (CP) and their effects on the growth and immunity in the Chinese mitten crab Eriocheir sinensis H. Milne Edwards, 1853, followed by a challenge assay with the white spot syndrome virus (WSSV) for ten days. Crabs were separately fed with CP-free, 0.5% CP, 1% CP, and 4% CP diets. Results showed that crabs fed with 1% and 4% CP diets exhibited significant higher growth rate than that of controls (P < 0.05). The acid phosphatase (ACP), alkaline phosphatase (AKP), and peroxidase (POD) activities in the 1% CP group were clearly higher than those in the control groups (P < 0.05). The contents of glutathione (GSH) in 1% CP and 4% CP groups were significantly higher than those in the control group (P < 0.05). Malondialdehyde (MDA) contents in experimental groups, especially in the 1% CP group, decreased significantly relative to those in the control group (P < 0.05). When challenged by WSSV, the cumulative mortality was the lowest in the 4% CP group, whereas that in the control group was the highest (P < 0.05). Our study revealed that CP-supplemented diets enhanced specific growth, antioxidant activity, and anti-WSSV resistance in E. sinensis. Based on our findings, we suggest a CP diet content of 10 g kg–1 (1%).