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Amphibian parasites of the genus Amphibiocystidium are members of the class Ichthyosporea (=Mesomycetozoea), within the order Dermocystida. Most of the species in the Dermocystida fail to grow in ordinary culture media, so their life cycle has only been partially constructed by studies in host tissues. However, to date, there have been few reports on the life cycle of Amphibiocystidium parasites with respect to the developmental life stages of both Dermocystidium and Rhinosporidium parasites. In this study, we provide light and electron microscopic findings of developmental phenotypes of Amphibiocystidium sp., a parasite previously characterized in the Italian stream frog (Rana italica), which has caused an ongoing infection in a natural population of Central Italy. These phenotypes exhibited distinct morphological characteristics that were similar to A. ranae from the skin of R. temporaria, but showed histochemical properties particularly comparable with those of maturing phenotypes of Rhinosporidium seeberi, and compatible with fungal-like parasites. Therefore, for Amphibiocystidium sp. phenotypes, we suggest adopting the terminology used for maturing stages of R. seeberi, such as juvenile sporangia, early mature sporangia and mature sporangia. The characterization of these developmental stages will be useful to increase the understanding of the life cycle of parasites of the genus Amphibiocystidium and of the interactions with their amphibian hosts.

Murray cod (Maccullochella peelii (Mitchell, 1838)) is an iconic Australian species, initially farmed mostly for stocking but now also for human consumption. Here, we report an infection with Dermocystidium sp., class Mesomycetozoea, order Dermocystida in the gills of Murray cod, from a hatchery in south-eastern Australia. Based on phylogenetic analyses of the 18S ribosomal DNA the parasite was closely related to D. salmonis, however the size of the spores was smaller than that reported for D. salmonis in other parts of the world. Further studies using additional analyses including ultrastructure of the spores would be useful for elucidating the identification of the microorganism. Histopathology showed inflammatory response and epithelial hyperplasia resulting in lamellar fusion particularly in association with the parasite. The condition was diagnosed as branchitis caused by a co-infection with Dermocystidium and epitheliocystis, with Dermocystidium being the dominant pathogen.

A species of Dermocystidium was discovered on the skin and fins of reared southern catfish Silurus meridionalis Chen. The parasite only appeared and caused disease in juvenile catfish at a water temperature of 18 to 23 degrees C. Marked external macroscopical clinical signs of the disease were sluggish movement of the fish, and the appearance of white filiform dermal cysts varying in size (3-20 mm in length and 0.15-0.35 mm in width). Examination of both fixed and fresh mounts for light microscopy and of samples for transmission electron microscopy (TEM) showed spherical spores (3.2-15 microm in diameter) with a peripheral nucleus (1.1-1.8 x 0.5-1.6 microm in diameter) and a prominent refractile body (2.08-10.83 microm in diameter) which occupied most of the volume of a mature spore. Three types of spore were identified, and are presumed to represent various developmental stages. Meanwhile, TEM showed the remnant nuclei in the residual plasmodium of a cyst, revealing its degenerative process. This paper represents the first observation and description of Dermocystidium sp. parasitizing catfishes.

Bullheads, Cottus gobio, with macroscopic external cysts on the skin and fins measuring up to 3 mm in diameter were detected in the River Allen and its tributaries in southern England between 1992 and 1998. The prevalence of these cysts was up to 50% at some sites. Examination of cyst contents revealed the presence of numerous spores, typical of the genus Dermocystidium, measuring 8 microm in diameter. The parasite developed within well-defined cysts, which were located in the hypodermal connective tissues of the host. No cysts were present on the fins of any of the fish examined. Histological examination revealed a cyst wall consisting of an inner layer of dense eosinophilic material similar to that reported for Dermocystidium spp. forming coenocytic hyphae. No evidence was found of systemic infection or hyphal formation. Spores contained a prominent refractile body, which gave a weakly positive reaction for polysaccharides with the periodic-acid Schiff reaction and was positively stained with acidic dyes. Several examples of ruptured cysts were seen in histological sections and in some of these cases the host epithelial layer was breached, allowing release of the spores to the environment. Morphological features of, and host response towards, the Dermocystidium sp. in bullheads are compared with similar infections in salmonids and other freshwater fish species.

In Finland Dermocystidium percae Reichenbach-Klinke was first recorded by Pekkarinen in the fins of a perch in 1988. Because it is a poorly known parasite, its occurrence and life stages are studied here. In occasional sampling during 1995-1998 and 2001, and more systematic sampling during 1999 and 2000 in two different lakes (one oligotrophic, the other slightly eutrophic), it was found to occur almost continuously, although sometimes very sparsely, in both lakes. The life cycle is maintained from year to year by overwintering cysts. Young perch acquire first infections in their first summer of life, and fish over 3 years possibly develop some immunity. In Estonia, in the Kasari River and the Matsalu Bay, the parasite seems to be very rare. Cysts of D. percae, capable of sporogenesis, can occasionally occur in the ruff, too. In perch in Finland, cysts were found differing from the longish and thin-walled cysts typical of D. percae. These roundish to dumbbell-shaped cysts with thicker walls are here sugge...

We report the enigmatic parasite Dermocystidium ranae in a green frog population (Solomeo, Umbria, Italy) of the Rana esculenta complex, consisting of the parental species R. lessonae (L) and hybrid form R. esculenta (E). In this population a rapid 50% decline of the parental form L was observed. Large dermal U-shaped cysts of D. ranae were found primarily on the ventral aspect of infected individuals, with a significantly higher incidence of infection in the parental species com- pared to the clonal hybrid. In each form, however, there was little pathological change associated with infection, and the cause of the recent declines of R. lessonae at this site remains unknown. In this paper we present the first ultrastructural description of an amphibian Dermocystidium sp. and we review the taxonomy of Dermocystidium, Dermosporidium and Dermomycoides spp. from amphib- ians. We conclude that Dermosporidium multigranulare Bro= & Kulda, 1954 is synonymous with Der- mocystidium ranae Guyenot & Naville, 1922 and, due to lack of sufficient differences between gen- era and significant dissimilarities with fish Dermocystidium spp., the 3 amphibian genera are synonymous. We propose that they should be designated to a new genus, Amphibiocystidium n. gen., and Dermocystidium retained for those species parasitic in fish.

A visceral form of a Dermocystidium-like organism was found at 13% prevalence in a carp and in 7·4% in a roach population from Greece. Successful experimental transmission was recorded only in carp. Pathology of the parasite in experimental fish and naturally infected fish was similar. ©1998 The Fisheries Society of the British Isles

An outbreak of Dermocystidium infection in cultured eels, Anguilla anguilla L., from Scotland is described. The disease appeared in the winter months but did not cause significant mortalities or adversely affect the growth of the eels. Infected eels had large, elongate white cysts on the gills. The cysts consisted of a homogeneous layer of parasite origin surrounded by a fibrous capsule and hyper-plastic epithelium. Within the cysts were small spherical parasite cells with a densely staining central area and peripheral granular, vacuolated cytoplasm. The cell wall appeared to be broken down in many cases and the cells appeared degenerate. The cysts eventually collapsed and the cavity was filled with epidermal tissue.

An epizootic of dermocystidiosis occurred among pond-cultured European eels, Anguilla anguilla for the first time at a fish farm in Shizuoka Prefecture. The fungus was identified as Dermocystidium anguillae which was first reported by SPANGENBERG (1975) in East Germany. The cysts were parasitic in the epithelial and connective tissues of the gills. Attempts were made to culture the parasite on some media, but without success.When the water temperature of tanks with the diseased eels was experimentally raised from 20°C to 30°C, the cysts disappeared from the gills of all the eels within a few days, which suggested that this disease could be cured by warm-water bathing.

Dermocystidium koi sp. nov. This species is found as a parasite; in one case it is parasiting to the integument and in another to the muscle of each separate Cyprinus carpis L. The specimen of the former was captured at the Yamada Fish Culture Farm (Locality-Yamada Village, Hyogo Pref., Date-July 23, 1940), and that of the latter obtained from the Seto Fish Culture Farm. (Locality-Vicinity of Odawara City, Kanagawa Pref., Date-May 11, 1959). In the case of integumentary parasitim, the parasites grow between the epidermis and the cutis in uarious places of the body surface without scales; and the characteristic lesions a e formed arising from the integument, due to the increase of the parasites and host's tissues such as fibrous connective tissueand blood vessels. (see text-fig. 1 and 2, A, B.) The muscular parasitism occurs when the parasites are parasitic to the scaley host; and in this case the parasites grow in the muscle near the body surface; on the infected parts, the large and hard tumor like inflammatory swelling arise from the increase of the parasites and the same host's tissues as the former. The parasite is filiform in external character; its transuerse section is round; the diameter 0.04-0.30mm., and it contains innumerable spares. Spare subspherical, 6-14μ in diameter; the diameter of the large characteristic spherical enclosure is 4.5-10.0μ. The details are compiled in the table 1. The spares are figured in text-fig. 3, NOS. 1-9. The present species is distinguishable from all other known species, in external form of the parasite or the cyst, the modus parasitic, and the dimension of the spare etc. The lesions may be ruptured naturally in a certa'n period; and the contents fall out from them; and then they seem to be healed gradually. Therefore, the host should not suffer great influence from the parasite. But the histological reactions of the host are marked, which are chiefly proliferocis inflammation, rarely accompanied with phagocytosis. (Text.-fig. 3, No. 10).

Dermocystidium Gasterostei n. sp., A Parasite of Gasterosteus Aculeatus L. and Gasterosteus Pungitius L.

Zoospores were obtained from a protist, parasitic in the clamMacoma balthica. It has been previously suggested that the parasite is either a closely related species or is the same species asLabyrinthomyxa marina (Dermocystidium marinum), which is found in the oysterCrassostrea virginica. The demonstration of zoosporulation and the description of zoospore micromorphology are here offered as evidence of similarity between the two parasites. The zoospores were biflagellated, pyriform cells with mastigonemes along one side of the anterior flagellum. Negative staining revealed substructure in the mastigonemes.

Dermocystidium marinum is a pathogen which kills oysters in Chesapeake Bay from July through October. The fungus proliferates readily only at temperatures above 25°C but overwinters in oysters as sub-clinical cases. Experiments were conducted in Nature to demonstrate the effects of proximity of infected oysters on epizootiology in isolated disease-free populations. Prevalence ofDermocystidium in the York River was moderate in 1957, heavy in 1959, and extremely low in 1963. In 1957, with 40 feet of isolation, groups mixed with infected oysters showed large increases in deaths and prevalences over controls. In 1959, the fungus was so widely prevalent in York River during a long hot summer that relatively minor reductions in death rates were obtained by 50 feet of isolation. In 1963, with the fungus nearly absent, a failure in laboratory infection techniques caused late timing of the experiment, and results were inconclusive. A new disease caused by “MSX”, a protistan parasite, developed high prevalences in the 1963 lots. This organism, by destroying oyster, populations in high-salinity waters (above 15‰ in late summer) has effectively reducedDermocystidium to a minor role as an oyster pathogen in lower Chesapeake Bay. Losses fromDermocystidium in Chesapeake Bay are dependent upon duration of warm seasons and survival of cases through winter. MSX, is slightly more sensitive to low salinities but much more tolerant of low temperatures thanDermocystidium. The decline ofDermocystidium with the disappearance of oyster populations suggests that the pathogen may be dependent solely upon transmission from oyster, to oyster.