| Parasite | Myxobolus aeglefini |
|---|---|
| Taxonomy | Myxozoa, Myxosporea, Bivalvulida |
| Hosts | Porous-head eelpout (Bothrocara hollandi), Haddock (Melanogrammus aeglefinus), Atlantic cod (Gadus morhua), Ling (Molva vulgaris), European hake (Merluccius merluccius), Lumpsucker (Cyclopterus lumpus), European plaice (Pleuronectes platessa), Dab (Limanda limanda) |
| Infection site | Trunk muscle (inside the cartilage tissue) in porous-head eelpout. Cartilage tissueof a head in the other fishes. |
| Clinical sign | Cysts are easily found by transmitted light even without dissection of porous-head eelpout (Fig. 1). Numerous round white cysts (about 3 mm in diameter) are observed in the trunk muscle (Fig. 2). |
| Parasitology | Many spores are produced inside cysts (Fig. 3). A spore (length 11.2-13.5 (average 12.0) mm; width 10.5-12.0 (11.0) mm; thickness 10.5-12.0 (11.0) mm) is subspherical, has 2 polar capsules (length 3.9-5.4 (4.5) mm; width 2.5-3.4 (2.8) mm) and shows a distinct mucous envelope around the posterior part. The life cycle is unknown. |
| Pathology | The parasite forms a cyst encased by cartilage tissue and thinly overlaid with connective tissue in porous-head eelpout. Occasionally, the spores are exposed between the muscle fibers adjacent to the cysts, suggesting that the spores were dispersed into the neighboring tissue after the rupture of cysts (Yokoyama and Wakabayashi, 2000). The diseased fish is rejected in the fish market due to its unsightly appearance. |
| Health hazard | Since this parasite is not infectious to human, it is harmless in food hygiene. |
| Diagnosis | Check the spores by wet-mount of cysts. Sample should be smeared and stained by Giemsa or Diff-Quik. |
| Other information | Although the range of host species is wide, most of the hosts are bottom fishes. The geographical distributions reported are the Sea of Japan, the North Atlantic Ocean, the North Sea and the Baltic Sea. Target organs of this parasite differ among the host species, but it infects to the cartilage tissue in all host species. |
| References | Yokoyama H. and H. Wakabayashi (2000): Myxobolus aeglefini found in the skeletal muscle of porous-head eelpout Allolepis hollandi from the sea of Japan. Fish. Sci., 66, 963-966. |
(Photos by S. Wakabayashi (1, 2))
Fig. 3. Fresh spores of M. aeglefini
Fig. 2.. Many cysts observed in the trunk muscle.
Fig. 1. Porous-head eelpout infected by M. aeglefini.