Prevention and Control Methods and Technical Key Points for the "Huaban" Disease in Sea Cucumber Aquaculture
This disease is also called “sliding board disease”, “board-shedding disease” and “disintegration disease”. It mostly occurs when barrel-shaped larvae metamorphose into five-tentacle larvae and in juvenile sea cucumbers after the larvae attach to boards. It is one of the most serious and commonly occurring epidemic diseases in the late stage of sea cucumber (Apostichopus japonicus) seedling rearing. The disease is highly contagious and develops quickly, and the mortality rate can approach 100% within a few days.
The main symptoms are: attached larvae contract and do not extend, tentacles contract, vitality decreases, attachment ability is poor, and they gradually lose the ability to attach to the substrate and sink to the bottom of the pond. Under an optical microscope, the epidermis of diseased larvae shows brown ‘rust’ spots and debris. Some diseased juvenile sea cucumbers are covered outside the body by a transparent film, the skin gradually ulcerates until disintegration, and ossicles scatter. Microscopic examination of the pond bottom shows large numbers of ossicles.
Analytical studies show that three strains of Gram-negative bacteria can cause this disease, and it has pathogenic diversity and complexity. One Vibrio strain has now been identified as one of the pathogenic bacteria. In terms of prevention and control measures: on the one hand, use secondary sand filtration or ultraviolet disinfection, promptly remove residual bait, feces, organic matter, etc., and change ponds at the appropriate time to minimize the number of pathogenic bacteria in the aquaculture water; on the other hand, pay attention to the quality and quantity of feeding, especially ensuring through disinfection treatment that bait such as sea mud and Sargassum thunbergii does not carry important pathogens. In addition, regular microscopic examination should be carried out to observe larval feeding, activity and health status. When disease is found, splash quinolone antibiotics in the pond, and treat with both medicated bathing and oral administration.