“Myxozoans detected in the gallbladders of farmed marine fishes in Japan (7109)”

Myxozoans detected in the gallbladders of farmed marine fishes in Japan

A disease characterized by emaciation has recently been reported in farmed greater amberjack (Seriola dumerili) in western Japan. Although the causative agent remains unidentified, myxospores of the genus Ceratomyxa have been frequently found in the gallbladders of affected fish. In Japan, only three species of gallbladder-infecting myxozoans have been reported from farmed marine fish to date, all in Seriola quinqueradiata. This study aimed to survey myxozoans in the gallbladders of various farmed marine fish in Japan.

The gallbladders of more than 200 individuals from 17 farmed marine fish species, spanning eight families including Carangidae, Oplegnathidae, Serranidae, Scombridae, Sparidae, Tetraodonidae, Monacathidae and Paralichthyidae, were examined for the myxozoan infection. Most of the fish were juveniles produced in hatcheries and reared in sea cages. When spores and/or development stages were observed in bile, parasites were identified based on morphology and molecular characteristics.

At least 16 distinct myxozoan species were observed in 11 different fish species. Among them, three species Myxobolus spirosulcatus, Ceratomyxa buri, and Ceratomyxa barnesi were identified. The other 13 species were not identified to the species level and are potentially undescribed. Out of 16 detected species, 12 species belonged to Ceratomyxa. Infection prevalence was high among amberjacks: more than 70% in S. dumerili, S. quinqueradiata and yellowtail amberjack (Seriola aureovittata). Mixed infections involving Ceratomyxa and Myxobolus were found in S. dumerili and red seabream (Pagrus major).

The infection cycles of these parasites are likely maintained within aquaculture sites. No apparent abnormalities were observed in the gallbladders or livers of fish host, and the presence of myxozoans was not consistently associated with emaciation or other clinical signs. Nevertheless, environmental and stress-related factors may enhance their impact to the fish host. Further pathological studies are needed in the future to better understand their potential role in fish health and effects on aquaculture. This study contributes to the understanding of myxozoan diversity in Japanese fauna.

1. Oe, Reika, Aquaculture Research Institute, Kindai University, Presenter
2. Chỉnh, Nguyễn Ngọc, Institute of Biology, Viet Nam Academy of Science and Technology, Author
3. Ishitani, Hiroe, Aquaculture Research Institute, Kindai University, Author
4. Yoshii, Keisuke, Fisheries Research Division, Oita Prefectural Agriculture, Forestry and Fisheries Research Center, Author
5. Shirakashi, Sho, Aquaculture Research Institute, Kindai University, Author