| Parasite | Argulus japonicus |
|---|---|
| Taxonomy | Arthropoda, Maxillopoda, Arguloida |
| Hosts | Common carp (Cyprinus carpio), goldfish (Carassius auratus) |
| Infection site | Skin |
| Clinical signs | Argulus japonicus (ca. 1 cm) is observed on the skin (Fig. 1). Diseased fish exhibits inflammation and haemorrhage in the lesions. |
| Parasitology | Argulus japonicus is a parasitic crustacean parasitizing the skin of warm water fishes. The body (length in female: 8-9 mm; male: ca. 6 mm) is flat and spherical (Fig. 2). It attaches the host’s body surface by the hook-shaped first antenna and the suckers derived from the maxillules. The parasite has a strong swimming ability because 4 well-developed swimming legs are located in the thorax. A female detaches the host and lays egg clusters in pond-wall and waterweed. Eggs hatch on about 15 days at 25 C., and larvae (copepodid) attach to the host’s body surface soon after hatching. The parasite becomes an adult and begins laying eggs in 3-5 weeks at 20-25 C. (Kimura, 1970). |
| Pathology | The lesions become eroded and haemorrhagic since Argulus pierces the host's skin with a preoral sting and injects toxic substances followed by feeding the leaked blood with a proboscis-like mouth. A heavily infested small fish is sometimes led to the death. |
| Health hazard | Since this parasite is not infectious to human, it is harmless in food hygiene. |
| Diagnosis | Argulus coregoni is a similar parasite to A. japonicus, but the former principally parasitizes coldwater fishes. A. japonicus can be morphologically differentiated from A. coregoni since the former is smaller and possesses a blunt end of the abdomen. Mixed infection of these two species has not been reported (Ogawa, 2004). |
| Other information | The parasite is effectively removed by the trichlorfon immersion, but repeated treatments are needed because it does not kill the parasite eggs. |
| References | Kimura, S. (1970):
Notes on the reproduction of water lice (Argulus
japonicus THIELE). Bull. Freshwater
Fish. Res. Lab. (Tokyo), 20, 109-126. (In Japanese) Ogawa, K. (2004): Metazoan diseases. Infectious and parasitic diseases of fish and shellfish. (ed. by Wakabayashi, H. and K. Muroga), Koseisha Koseikaku, pp.381-405. (In Japanese) |
(Photos by K. Yoshizawa)
Fig. 1. Goldfish heavily infected by A. japonicus (arrows).
Fig. 2. Male adult of A. japonicus.