| Parasite | Clinostomum complanatum |
|---|---|
| Taxonomy | Platyhelminthes, Trematoda, Strigeidida |
| Hosts | Many freshwater fishes including oriental weatherfish (Misgurnus anguillicaudatus), crucian carp (Carassius auratus) and ayu (Plecoglossus altivelis). |
| Infection site | Muscle near the skin |
| Clinical signs | Yellowish-white ellipsoidal encysted parasites (ca. 2 mm in length) are visually observed (Fig. 1). |
| Parasitology | The parasite in fish is a metacercaria of Clinostomum complanatum (ca. 5 mm in size) (Fig. 2). Cercariae of C. complanatum are released from snails (the first intermediate host), and infect to fishes (the second intermediate host). The parasite encysts in the muscle near the body surface of fish and become metacercariae. They utilize fish-eating birds as the definitive host and parasitize their oral region and oesophagus (Ogawa, 2006). |
| Pathology | Generally, its pathogenicity is low. However, heavily infested fish exhibit growth retardation. Some authors reported that there were mass mortalities of cultured ayu (Lo et al., 1981; 1985; Yanohara, 1989). The parasite is harmful for fish when stimulated by pharmacological agents or changes of water temperature, because it excysts and pierces the skin to leave the host in such occasions (Lo et al., 1985). The peripheral tissues become congestive and haemorrhagic, leading to the host's death. |
| Health hazard | This parasite can infect to the pharynx of humans, causing the pharyngitis. It can be readily removed surgically, but avoid eating raw oriental weatherfish. |
| Diagnosis | Check the morphology of an excysted metacercaria. |
| Other information | Yanohara (1989) reported that the prevalence in cultured oriental weatherfish fry in Japan was 8 %, and that outbreaks occurred in cultured ayu in Taiwan. It is recommended to prevent from the invasion of snails and birds by using well water and nets, respectively. |
| References | Lo, C.-F., F. Huber,
G.-H. Kou and C.-J. Lo (1981): Studies of Clinostomum
complanatum (Rud., 1819). Fish Pathol.,
15, 219-227. Lo, C.-F., S.-C. Chen and C.-H. Wang (1985): The study of Clinostomum complanatum (Rud., 1819) V. The influences of metacercaria of Clinostomum complanatum on fish. Fish Pathol., 20, 305-312. Ogawa, K. (2006): Yellow grub infection. New atlas of fish diseases (ed. by Hatai, K. and K. Ogawa), Midori Shobo, p. 41. (In Japnese) Yanohara, Y. (1989): Yellow grub infection. Atlas of fish diseases (ed. by Hatai, K., K. Ogawa and H. Hirose), Midori Shobo, p.226. (In Japanese) |
Fig. 2. Metacercaria of C. complanatum.
(Photo by K. Ogawa)
Fig. 1. Oriental weatherfish parasitized by C. complanatum.