In vivo infestation and life cycle observation of marine leech Zeylanicobdella arugamensis

Abstract:

Zeylanicobdella arugamensis is an important ectoparasitic leech that can infest more than 30 species of marine fish. Diseases associated with Z. arugamensis are prevalent in China and many countries of Southeast Asia, and frequently cause the death of cultured marine fishes. In order to continually and steadily provide sufficient live leeches and cocoons for the research of the prevention and treatment of Z. arugamensis, this study established a propagation method for Z. arugamensis through in vivo infestation experiments, and proved that two ornamental fish species, spinecheek anemonefish (Premnas biaculeatus) and tomato anemonefish (Amphiprion frenatus), were suitable for use as fish hosts. The parasite descendants generated by the in vivo propagation method are still very transmittable after nine generations. This study also used micrography to observe cocoons and the life cycle of propagated fish leeches. The results showed that the average cocoon size of Z. arugamensis was (0.66±0.06) mm, and there was only one fertilized egg in each cocoon. The life cycle of Z. arugamensis can be divided into two stages: The cocoon hatching stage and the juvenile development stage. Under a seawater temperature of 26℃ and salinity of 30, Z. arugamensis can complete its life cycle in as short as 20 days. The cocoons of Z. arugamensis developed into juvenile leeches in nine days, with a hatching rate as high as 83.8%. The juvenile leeches subsequently infected the host fish, grew to mature adults, and produced new cocoons in 11 days. This article confirmed for the first time that P. biaculeatus and A. frenatus were both susceptible hosts for Z. arugamensis. This study not only established an in vivo propagation method for Z. arugamensis, but also provided technical support for research on the pathogen, pathology, pathogenic mechanism, detection, and prevention of leech diseases related to Z. arugamensis.