Abstract:The cultured juvenile sea cucumber (Apostichopus japonicus) sufferred from "enteritis disease" in a breeding farm in Penglai in March 2014. In this study, the clinical symptoms and histopathology of enteritis disease were investigated. To provide reliable means to control this disease, the pathogen was isolated and identified, and its sensitivity to different antibiotics were tested. The effects of different therapeutic methods (oral, bath, oral with bath) were evaluated using three indices, including the ratio of viscera to body wall (RVBW), weight gain rate (WGR) and specific growth rate (SGR). The results showed that the sea cucumber infected with the enteritis disease displayed dark body color, poor feeding rate, weak motility and adhesion ability. The ingested food in the intestine of sick sea cucumber was discontinuous, and large amount of yellow-white mucus was found in the intestine. The intestinal wall was brittle, poor toughness and easy to fracture. A large amount of bacteria was detected in the intestinal tract under the microscope. The histopathological analysis on infected sea cucumbers revealed the scattered intestinal villus, dispersed mucous layer, scattered connective tissue and obviously separated muscle layers. One dominant bacterium (In-1) was isolated from the infected sea cucumber intestine and was confirmed as the causative pathogen using the artificial infection experiment. The bacteriological analysis indicated that the deteriorated feed (algae powder) was most likely the origin of the pathogen. The pathogen was identified as Vibrio harveyi using morphology observation, physiological and biochemical, and molecular methods (16S rDNA and gyrB). The strain was highly sensitive to 12 kinds of drugs such as ceftriaxone, azithromycin, doxycycline and florfenicol. The medication treatment using florfenicol with three different methods showed that medicated bath treatment was the most effective and achieved the best results of the WGR of (24.23±0.41)% and SGR of (0.77±0.01) %/d. The study provides the theoretical basis and technical reference for disease prevention and control in sea cucumber culture and its healthy breeding.
