| Parasite | Bivagina tai |
|---|---|
| Taxonomy | Plathyhelminthes, Monogenea, Polypisthocotylea |
| Host | Red sea bream (Pagrus major) |
| Infection site | Gill |
| Clinical sign | Parasite (a few mm) attaches on the gill filament (Fig. 1). Heavily infected fish exhibits anorexia and emaciates. |
| Parasitology | Elongate body of the parasite is 3-4 mm long (Fig. 2). The parasite attaches on the gill by 2 pairs of haptors at the posterior end. Right and left clamps are approximately the same size and the number is a total of 80-130. The hermaphroditic adult produces spindle-shaped eggs with threads at both sides. The eggs are not linked each other. |
| Pathology |
Heavily infected fish exhibits the anaemic gill. Some infected fish die by infection. |
| Health hazard | Since this parasite is not infectious to human, it is harmless in food hygiene. |
| Diagnosis | Adult parasites attaching the gill filament can be visually seen, while immature parasites are observed by flattened samples of the gill under the light microscope. |
| Other information | The infection has a seasonal fluctuation. The 0-year fish has the highest level of infection in winter, when the affected fish is extensively damaged. The infection level increases again in early summer, when the water temperature reaches about 20 C, but little damage is observed. As the temperature further increases,parasite intensity also decreases. The optimal temperature for the parasite propagation is 20 C and below. The winter propagation may be related to the hostfs vulnerability caused by low water temperature (Ogawa, 1988). A bath treatment with a hydrogen peroxide solution can be used for control of the parasite. |
| References | Ogawa, K. (1988): Occurrence of Bivagina tai (Monogenea: Mycrocotylidae) on the gills of cultured red sea bream Pagrus major. Nippon Suisan Gakkaishi, 54, 61-64. |
(Photo by K. Ogawa)
Fig. 1. A stained specimen of Bivagina tai