A list of myxozoan genera is presented in the current taxonomical scheme. These genera are defined; their type species and most important pathogens along with their hosts are listed. Simultaneously, definitions of actinospore stages representing sexual stages of the myxosporean life cycle are given; altogether, 17 actinospore collective groups with 180 types have been described. Life cycles of the two classes of the phylum Myxozoa, Malacosporea and Myxosporea, are briefly outlined with specification of the appropriate terms. Up to now, 4 malacosporean and 2,180 myxosporean species assigned to a total of 62 genera, have been established. The surviving classification of myxosporeans, based on spore morphology, is discussed in the context of the still fragmentary data resulting from SSU rDNA sequence analyses. The main task for the future is a rigorous, detailed morphological description combined with molecular techniques in establishment of new species and in revision of the existing ones. Establishment of a classification acceptable from morphological, biological and phylogenetical viewpoints is necessary.

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Myxozoan genera: definition and notes on taxonomy, life-cycle terminology and pathogenic species.

The phylogenetic study on Thelohanellus species (Myxosporea) in relation to host specificity and infection site tropism.

A description is given of a new myxozoan parasite located in the intestinal wall of the cultured carp Cyprinus carpio from Japan. The name Thelohanellus kitauei n. sp. is suggested for this parasite whose spores are characterized by an egg-shaped balloon-like sack, 33.4μm by 15.0μm in size in average. Spores measure 26.3μm in length and 9.2μm in breadth and thickness in average in water. The polysporous vegetative form which forms a giant polyp-like swelling in the intestine is inferred to be a single winding tube based on histological observations of the serial paraffin sections of the swellings. A mass of minute spherical disporous form is exceptionally observed in a small visible lesion lying under the mucosa, too.

A New Myxozoa Thelohanellus kitauei,the Cause of Intestinal Giant Cystic Disease of Carp (魚病に関する国際セミナ-)

Thelohanellus infection of the scales of the European wild carp Cyprinus carp10 carplo L 1s reported for the first time in Europe Comparative morphological and histological f i nd~ngs are descnbed Plasmodia and spores found In the fins of cultured common carp fingerlings and those detected in the scales of 2to >4-yr-old European wild carp belong to the same species The morphological chardcteristics of the spores and histolog~cal analysls of plasmodlal locat~on suggest that the species is ident~cal wlth Thelohanellus nikolskii Achmerov 1955 The authors regard T cypnni Hoshina & Hosoda, 1957 and T calhsporis Ky, 1971 as Iunlor synonyms of T nlkolsk~l Achmerov 1955

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Thelohanellus (Myxozoa: Myxosporea) infection of the scales in the European wild carp Cyprinus carpio carpio.

Allogynogenetic silver crucian carp, Carassius auratus gibelio (Bloch), has become cultured on a large scale in recent years in China, especially in the middle and lower reaches of the Yangtze River Infection with myxosporeans has resulted in large losses of ®sh stocks (Xu, Wang, Wu, Qiu, Li & Hu 1997; Wang, Wang, Lu, Li & Zhang 1998; Wu 1998) Although many species of myxosporean have been described as pathogens of ®sh in China (Pan 1988; Wu & Wang 1997; Chen & Ma 1998), there are no reports on diseases caused by species of the genus Thelohanellus Thelohanellus wuhanensis Xiao et Chen, 1993 was ®rst identi®ed on the skin of allogynogenetic silver crucian carp in Wuhan City and Jingshan County of Hubei Province, China It is somewhat similar to T hovorkai Achmerov, 1960 except for the spore shape and dimensions (Xiao & Chen 1993) Severe disease caused by T hovorkai is well known (MolnaÂr & KovaÂcs-Gayer 1986; Yokoyama, Liyanage, Sugai & Wakabayashi 1998, 1999) as is that caused by T kitauei (Rhee, Kim, Kim & Park 1990; Rhee, Kim & Park 1990, 1993) T wuhanensis was ®rst found to cause serious disease in juvenile allogynogenetic silver crucian carp on many ®sh farms around Wuhan City in 1999 Mortality of heavily infected fry was usually observed The present study surveys the infection of T wuhanensis on juvenile allogynogenetic silver crucian carp in a ®sh hatchery of Wuhan City and a ®sh farm in Ezhou City In addition, a treatment test against thelohanellosis using fumagillin was conducted One-month old allogynogenetic silver crucian carp fry (n  288) were collected from a ®sh hatchery at Caidian District in Wuhan City on 10 June 1999 Fish more than 2-months-old were collected from a ®sh farm in Ezhou City, Hubei Province in July, September, October and November 1999 (n  30 each) The ®sh had recently been transferred from the hatchery in Wuhan City on 10 June The geographical localities of the two sampling sites are shown in Fig 1 Examination for the spores of T wuhanensis was made according to the methods described by Yokoyama et al (1998) Plasmodia larger than 03 mm diameter were used to estimate the degree of infection Plasmodia were observed, measured and counted under a dissecting microscope The experimental use of fumagillin against thelohanellosis was assessed using two small ponds (about 600 m in area and 1 m in depth) in the Ezhou City farm A total of 200 kg ®sh (body Journal of Fish Diseases 2001, 24, 57±60

Occurrence of thelohanellosis caused by Thelohanellus wuhanensis (Myxosporea) in juvenile allogynogenetic silver crucian carp, Carassius auratus gibelio (Bloch), with an observation on the efficacy of fumagillin as a therapeutant

In an attempt to develop prophylactic and therapeutic measures of the intestinal giant-cystic disease caused by Thelohanellus kitauei in the Israel carp, Cyprinus carpio nudus, pathological observations were conducted upon the carps which were hatched in May 1988 and raised in a net cage fish farm at the Soyang lake, managed by Horim Fisheries for the period of 21 months with 1-2 months interval. After a gross inspection of the carps, necropsy was carried out periodically in order to clarify the pathological changes in various internal organs and muscular tissues. Also, the prevalence of the disease was checked during the period from 1988 to 1990. Gross inspections revealed that the infected carps showed some degree of fading in body and gill color, back-emaciation symptoms, reddish anus accompanying erosion and relaxation and pot-belly, as well as discharge of yellowish white mucoid material from the anus. However, most carps died eventually of intestinal obstruction. Other significant necropsy findings included cyst formation of various size in the intestinal mucosa, ascites, anemic condition through internal organs and muscular tissues, hyperemia and dilation of intestines with decreased tension, thinness and fragility, and full contents of semi-fluid or yellowish white mucoid material in the intestinal canals. Based on the morphological characteristics of the spores found in the cysts, parasitic location in the intestines, macro- and microscopic findings of the lesions, the parasites were identified as Thelohanellus kitauei Egusa et Nakajima, 1981. Although monthly changes of water temperature were distinct, the extrusion rates of the polar filaments of the spores stayed constant throughout the year with an exception of a lower rate in July. The lesions initiated from mucosa and submucosa in early July became large swellings and then complete mature forms following the peracute course. From late August the upper cysts were gradually opened and most of the spores were dispersed from anus into the surrounding water through December but only a few lasted until next April. The cysts were completely recovered until next September. Comparing the incidence and prevalence of the disease by year tremendous infection and death rates were checked in the first prevalent year, 1988, but the rates were significantly decreased in the second year, and showed an almost normal status in the third year, 1990. As the above summarized results showed, the disease entity might come to an end in three years after the first prevalent year, however, the spores must be strictly prevented because they could be infective in the water for one year.

[Prophylactic and therapeutic studies on intestinal giant-cystic disease of the Israel carp caused by Thelohanellus kitauei. I. Course of formation and vanishment of the cyst].

P G Kim

Papers

[Prophylactic and therapeutic studies on intestinal giant-cystic disease of the Israel carp caused by Thelohanellus kitauei. I. Course of formation and vanishment of the cyst].