Fig. 1. A spore of Kudoa neothunni stained by Diff-Quik,
| Parasite | Kudoa neotunni |
|---|---|
| Taxonomy | Myxozoa, Myxosporea, Multivalvulida |
| Hosts | Yellowfin tuna (Thunnus albacares), Bigeye tuna (Thunnus obesus), Northern bluefin tuna (Thunnus thynnus) |
| Disease name | Post-mortem myoliquefaction |
| Infection site | Trunk muscle |
| Clinicla sign | No external signs are visually evident. Liquefaction of the trunk muscle, viz. post-mortem myoliquefaction is observed. In the early stage of infection, rice grain-sized whitish spots are widely observed. In the advanced stage, almost all trunk muscle become a liquid condition (Konagaya, 1975). |
| Parasitology | Many spores are observed in the affected area. A spore (lengh 6.2 (5.3-7.3) μm; width 11.0 (9.1-13.0) μm) has 6 polar capsules. The life cycle is unknown. |
| Pathology | The neighboring tissues are disintegrated and liquefied by the proteolytic enzymes derived from the parasite (Konagaya, 1982). Such disintegrations are not observed just after the catch and develop after death of the host fish. |
| Health hazard | Since this parasite is not infectious to human, it is harmless in food hygiene. |
| Diagnosis | Check the spores by wet-mount of the liquefied muscle tissue. Sample should be smeared and stained by Giemsa or Diff-Quik. |
| Other information | This disease was called as “adzuki” at fish markets because of the adzuki bean-like hole in the trunk muscle. This parasite was firstly described as Hexacapsula neothunni due to its 6 polar valves and 6 polar capsules (Arai and Matsumoto, 1953). However, this species was transferred to the genus Kudoa by the molecular phylogenic analysis (Whipps et al., 2004). There are no effective methods to prevent this disease. |
| References | Arai, Y. and K.
Matsumoto (1953): On a new sporozoa, Hexacapsula
neotunni gen. et sp. nov., from the muscle of yellowfin tuna, Neothunnus macropterus. Bull. Japan. Soc. Sci. Fish., 18, 293-299.
Konagaya, S. (1975): Jellied meat in fish. Sakana, 15, 32-39. (In Japanese) Konagaya, S. (1982): Histological observation of jellied yellowfin tuna meat. Bull. Tokai Reg. Fish. Res. Lab., 106, 55-75. (In Japanese) Whipps, C. M., G. Grossl, R. D. Adlard, H. Yokoyama, M. S. Bryant, B. L. Munday and M. L. Kent (2004): Phylogeny of the Multivalvulidae (Myxozoa: Myxosporea) based on comparative ribosomal DNA sequence analysis. J. Parasitol., 90, 618-622. |