Antibiotics and chemical disease-control agents reduce innate disease resistance in crayfish

The aquaculture industry has developed rapidly in recent years, and in China Crayfish Procambarus clarkii represent an important aquaculture fishery. However, bacterial and viral diseases are becoming an increasingly serious threat, causing considerable economic losses. Farmers use a large number of drugs and chemicals to destroy pathogenic microorganisms and to purify aquaculture water. The purpose of this study was to assess the effects of such drugs on crayfish immune systems. Five of the most commonly used fishery drugs and water treatment chemicals were analyzed: norfloxacin, calcium hypochlorite, quick lime, povidone iodine and copper sulfate. Crayfish immune activity tests revealed that total hemocytes counts, as well as the activities of phenoloxidase and superoxide dismutase, decreased following exposure to all five treatments. These treatments, especially calcium hypochlorite and norfloxacin, significantly enhanced hemocyte apoptosis in crayfish, regardless of disease status. Calcium hypochlorite, in particular, led to a significant decrease in the survival rates of crayfish infected with white spot syndrome virus or Vibrio alginolyticus. Our results indicate that water treatment and disease control compounds commonly used in aquaculture can reduce the innate immunity and therefore disease resistance of crayfish.