Etiology of rotting edges syndrome in cultured larval Apostichopus japonicus at auricularia stage and analysis of reservoir of pathogens

Abstract:

Abstract：【Objective】This study was to clarify pathogens and its sources of the disease called rotting edges syndrome at the auricularia stage in the larval culture of Apostichopus japonicus, and further to find out effective medicines for this disease.【Methods】Etiological analysis was performed on larvae with typical rotting edges syndrome from larvae culture farm. Suspicious pathogen was used for artificial infection test, and then identified through morphological, physiological/biochemical tests, and 16S rDNA sequence analysis. Bacterial analysis on the culture system of the factory, including water sources, feeds，rearing water, bottom ordure and water from cultivation pond for parent sea cucumber, was carried out. Finally, drug-sensitive tests were performed on the pathogens.【Results】A common dominant bacterium strain was isolated from all ill larvae included in the study. Artificial infection test showed it was the causative pathogen associated with the disease, and the artificially infected sea cucumbers had the same syndromes to the naturally ill ones. The bacterium was identified as V. lentus. Bacterial quantity of rearing water system were at a high range (2.8 × 102–8.8 × 107 cells/mL). The sources of the pathogen were complicated, since pathogens were discovered in the rearing water, bottom ordure and water from cultivation pond for parent sea cucumber. However, the density of causative bacteria was the highest in the bottom ordure, middle in the rearing water, and lowest in the water from cultivation pond for parent sea cucumber. Fifteen antibiotics could inhibit growth of the pathogens.【Conclusion】The possible pathogen for rotting edges syndrome was V. lentus. The bottom ordure, rearing water and parent sea cucumber may be the main infective origin of the pathogen. Fifteen antibiotics including neomycin, could be applied for disease prevention and treatment of Apostichopus japonicus.

Key words:Keywords：Apostichopus japonicus; rotting edges syndrome; pathogen; identification; source; prevention and treatment