Parasite Myxobolus sp.
Taxonomy Myxozoa, Myxosporea, Bivalvulida
Hosts Crucian carp (Carassius auratus), Prussian carp (Carassius gibelio)
Infection site Head, fin, skin
Clinical signs Many white cysts are observed on the head, in particular, the mouth region (Fig. 1).
Parasitology A number of spores are formed inside the cyst (Fig. 2). A spore (length 9.2 (8.4-9.8) mm; width 8.2 (7.8-8.4) mm; thickness 5.5 (5.4-5.8) mm) is almost round and has 2 equal polar capsules (length 4.5 (3.6-4.8) mm; width 2.8 (2.4-3.0) mm) (Chen and Ma, 1998). The life cycle is unknown.
Pathology Although this disease is not fatal to the host fish, the market value of infected fish is reduced (Lu et al., 2002).
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 cysts. Sample should be smeared and stained by Giemsa or Diff-Quik.
Other information This disease occurred some cultured crucian carp in China. It was identified as Myxobolus rotundus, and several immunological studies were conducted (Lu et al., 2002; Lu et al, 2003; Zhang et al., 2006). However, it is probably not the same species with M. rotundus due to their different gene sequences of SSU rDNA (K. Molnar, personal communication).
References Chen, Q. L., and C. L. Ma (1998): Myxozoa, Myxosporea. Fauna Sinica. Beijing, Science Press, 987 p.

Lu, Y. S., M. Li, Y. S. Wu and J. G. Wang (2002): Antigenic study of Myxobolus rotundus (Myxozoa: Myxosporea) using monoclonal antibodies. J. Fish Dis., 25, 307-310.

Lu, Y. S. P. Nie and B. J. Sun (2003): Detection of Myxobolus rotundus (Myxozoa: Myxosporea) in skin mucus of crucian carp Carassius auratus auratus using monoclonal antibody. Dis. Aquat. Org., 54, 171-173.

Zhang, J. Y., J. G. Wang, Y. S. Wu, M. Li, A. H. Li and X. L. Gong (2006): A combined phage display ScFv library against Myxobolus rotundus infecting crucian carp, Carassius auratus auratus (L.), in China. J. Fish Dis., 29, 1-7.

Fig. 2. Fresh spores of Myxobolus sp.

(Photos by Jin-Yong Zhang)

Fig. 1. Heavily infected crucian carp around region of the mouth.