| Parasite | Henneguya lateolabracis |
|---|---|
| Taxonomy | Myxozoa, Myxosporea, Bivalvulida |
| Host | Chinese sea bass (Lateolabrax sp.) |
| Disease name | Cardiac henneguyosis |
| Infection site | Heart |
| Clinical sign | Diseased fish exhibits anorexia and lethargy followed by the death. Typical signs are anemia and increased mucus secretion in the gills (Fig. 1), inflammation and enlargement of the heart (Fig. 2) and anemia in the internal organs. |
| Parasitology |
A number of spores fully occlude the capillary of the gill filament (Fig. 3). A spore (length 9.9-11.9 (average 10.7) mm; width 6.4-7.8 (7.5) mm; thickness 5.9-6.4 (6.2) mm) is ovoid and has 2 polar capsules (length 3.0-4.0 (3.4) mm; width 1.5-2.0 (1.7) mm ) and 2 caudal appendages (30.7-49.5 (37.7) mm). The life cycle is unknown. |
| Pathology | Mature spores are produced inside the bulbus arteriosus followed by the invasion into the gill filament leading to occlusion of the capillary, congestion, lamellar fusion and destruction of gill epithelia (Fig. 5) (Yokoyama et al., 2003). |
| Health hazard | Since this parasite is not infectious to human, it is harmless in food hygiene. |
| Diagnosis | Check the spores by wet-mount of squashed gill filament or enlarged bulbus arteriosus. Sample should be smeared and stained by Giemsa or Diff-Quik. |
| Ohter information | This disease occurred in Chinese sea bass at the seedling stages imported from China. At first, it was suspected that this parasite was transferred to Japan from China through the transportation of seedlings of Chinese sea bass. However, the life cycle of this parasite might has been already established in Japan because domestically produced Chinese sea bass were found to be infected. Disease outbreaks occur from December in the year of seed introduction, and continued until June of the following year. The mortality is chronic. Though there are no effective measures to prevent this disease, infected fish would recover after the spores were completely released outside the host. |
| References | Yokoyama, H., H. Kawakami, H. Yasuda and S. Tanaka (2003): Henneguya lateolabracis sp. n. (Myxozoa: Myxosporea), the causative agent of cardiac henneguyosis in Chinese sea bass Lateolabrax sp. Fish. Sci., 69, 1116-1120. |
Fig. 1. Anaemia and mucus secretion in the gill.
(Photos by H. Obata (1, 3))
Fig. 5. Clubbing of the gill filament and detachment of epithelia.
Fig. 2. Enlargement of the bulbus arteriosus
Fig. 3. Spores occluded in the gill capillary.
Fig. 4. Fresh spores of H. lateolabracis
