Effect of environmental factors on the control of milky disease in Chinese mitten crab (Eriocheir sinensis)

Abstract

“Milk disease”, a relatively serious disease with a high infection and mortality rate, frequently threatens the aquaculture of the Chinese mitten crab area, especially in northern China in recent years. To explore effective measures on the “milky disease” control, gradient temperature and pH were designed for the aquaculture of the infected crabs according to the reproductive characteristics of the pathogens. Then, the tissue slice and the immune capacity were detected to analyze the treatment resulting response on the organism immune system; and the bacterial and fungal flora distribution of the hepatopancreas was analyzed to judge the trend of disease development. The results found that low temperature (16 °C) significantly increased the survival percentage of the infected crabs (p < 0.05), which weakened the damage of the immune system and enhanced immunoenzyme activities (p < 0.05), but without any significant change in the microbial flora structure, indicating low temperature delayed the onset of disease and can effectively gain time for further treatment and cure measures. High temperature decreased the survival percentage (p < 0.05), but the only survived crabs showed a much higher immunocompetence and a reduced percent of community abundance of the pathogen in vivo (p < 0.05). These crabs prompted the characteristics of the “cured” crabs and suggested immunity promotion and the competition/inhibition of the pathogen in vivo would be significant for the prophylaxis and treatment of the milky disease. The survival percentage and fluctuant enzyme activities of alkali-pH groups manifested that alkali pH brought a positive response in the preliminary stage but damaged the immune system of the infected crabs, indicating it is essential to reappraise the adaptability to environmental factors in the infected crabs for disease control. This study is of crucial meaning for establishing new strategies for prevention and control of the “milky disease”.