Search

A serious outbreak of mortalities occurred among adult salmon held in the Priest Rapids Dam spawning channel in November 1965. Gross examination revealed small, white cysts on and in the gill filaments of otherwise normal-appearing fish. Approximately 25% of the 5000 mature adult salmon in the channel died prior to spawning from this disease caused by a fungus identified as the genus Dermocystidium. This is the first record of an epidemic among fish of North America associated with Dermocystidium. The primary cause of death appeared to be anoxia due to subacute inflammation and granulation of the gill tissue. A description of the histopathology associated with these parasites is given. Chondrococcus columnaris, a pathogen of warm-water fishes, was present as a secondary invader on the gill filaments of several salmon and an unknown fungal or yeast-like organism was present in the testes of the male fish examined.

1. 1. Fatty acids of four marine fungi Thraustochytrium roseum, T. aureum, Schizochytrium aggregatum and Dermocystidium sp. and one fresh-water fungus Phlyctochytrium punctatum were determined. 2. 2. These fungi synthesized ω 3 and ω 6 polyunsaturated fatty acids. They contained large quantities of C20 and C22 polyenes; three of the marine fungi contained unusually large amounts of 22:6 fatty acid. 3. 3. Major fatty acids for T. roseum and S. aggregatum were palmitic, oleic and docosahexaenoic acids; for T. aureum, palmitic, docosapentaenoic and docosahexaenoic acids; for Dermocystidium, palmitic, palmitoleic and eicosadienoic acids; for P. punctatum, palmitic, stearic, oleic and linoleic acids. 4. 4. The pattern of biosynthesis of polyunsaturated fatty acids by these aquatic fungi as well as their morphology supports the hypothesis that they evolved from a primitive phytoflagellate (monad) ancestor.

Serious outbreaks of a pernicious disease caused by the fungus Dermocystidium are reported in both adult and juvenile salmon in the Columbia River and its tributaries. The disease evokes a characteristic histopathology and appears to cause death in a large percentage of the infected fish. The disease appears to be most virulent at water temperatures below 60 F. Some prophylactic relief is given by treatment with the organic herbicide, Diquat, at a dilution of 1:500,000 for 1 hr.

Twelve antifungal antibiotics were screened to determine their potential for controlling Dermocystidium marinum, a lethal fungus parasite of oysters. Two antibiotics, cycloheximide and streptimidone, completely inhibited enlargement of D. marinum in thioglycollate cultures at concentrations of 0.25–1.0 μg/ml. Cycloheximide shows promise for use in arresting D. marinum infections in oysters held in closed laboratory systems. Twenty-two antibacterial antibiotics were screened for their effect on the enlargement of D. marinum in thioglycollate cultures, and for their efficacy in retarding growth in bacteria associated with oyster tissues. Three tetracyclines (tetracycline, chlortetracycline, and oxytetracycline), bacitracin, and gramicidin showed effective antibacterial properties at levels of 250–500 units or mcg/ml. However, all of these agents except gramicidin markedly inhibited parasite enlargement at concentrations of 250–750 units or mcg/ml. Further studies proved gramicidin to be inferior to either chloramphenicol or the penicillin-dihydrostreptomycin combination for inhibiting bacterial growth and tissue putrefaction in the thioglycollate culture technique for detecting D. marinum.

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

Dermocystidium has been recorded from oysters (Mackin et al., 1950), numerous species of freshwater fish and some Amphibia (Reichenbach-Klinke and Elkan, 1965). The taxonomic affinities of the group have been uncertain until recently when Perkins (1976) demonstrated that Dermocystidium marinum from oysters, previously considered by many workers to be a fungus is, in fact, a member of the protozoan phylum Apicomplexa, since it possesses a zoospore stage containing an apical complex. Subsequently Levine (1978) erected a new genus Perkinsus to distinguish the oyster parasite from those found in fish and Amphibia and placed it in a new class Perkinsea, within the Apicomplexa. The relationship between the invertebrate and vertebrate parasites is not clear because of the lack of information on developmental stages of the latter group.

The life cycle of a nonfilamentous marine phycomycete, Dermocystidium sp., is described from its growth in axenic culture under controlled conditions. Reproduction occurs by vegetative means involving a process of cell enlargement and ecdysis modifiable by the methods of cultivation. Zoospores and sexuality were not observed. The results of inoculation studies with algae, phanerogam debris, and molluscs suggest that the fungus may be a free-living saprophyte in coastal waters.

The microstructure of the protist Labyrinthomyxa marina as found in a host organism, Crassostrea virginica, is described. Most of the organelles were similar to those of many eucaryotic protists; however, a few unusual structural features were observed. Viruslike particles (460–530 A diameter) were found in the nucleus and cytoplasm of the Virginia, but not the Florida, pathogens. Cell-wall formation appeared to occur, in part, by formation of material in vesicles derived from the endoplasmic reticulum. The vesicles appeared to fuse with the plasmalemma and release material into the cell wall. Funguslike lomasomes were found between the cell wall and plasmalemma. Vacuoplast formation occurred by synthesis of droplets of electrondense material through the membranes of large vacuoles followed by coalescence to form one or two large vacuoplasts. Mitochondria were involved in the formation of vesicles which contained electron-dense material and which were delimited by two membranes. Since L. marina has previously been allied with the Labyrinthulia (Protozoa) and the Saprolegniales (Phycomycetes), comparisons are made with the ultra-structure of representatives from both groups. Affinities with the fungi seem to be the closest on the strength of lomasome formation and the repeated formation of cell walls in all vegetative stages.

In the skin of Rana temporaria from Czechoslovakia two unicellular parasites have been found: Dermocystidium ranae Guyénot & Naville and Dermosporidium granulosum n.sp.Dermocystidium ranae. Two stages were found, one of which is new. An account is given of the morphology, development and occurrence of both stages, including details which have hitherto not been recorded.Dermosporidium granulosum n.sp. This species is represented by cysts situated in the stratum spongiosum corii. They are divided by septa into small chambers containing groups of spherical spores with a central nucleus and with numerous small cytoplasmic inclusions. Within the cyst, the sporoblasts occupy the periphery, while the ripe spores are in the centre.

10 páginas, 3 tablas, 5 figuras, Parasites identified as Perkinsus atlanticus have been reported infecting carpet shell clams in Galicia (northwest Spain). We have sequenced the 18S ribosomal RNA gene of in vitro cultured Perkinsus atlanticuslike or hypnospores from diseased clams, and compared it with the same genomic region from P. marinus and Perkinsus sp. We have also compared the sequence of internal transcribed spacer (ITS) 1, ITS 2, and 5.8S rRNA from our isolate with the P. atlanticus GenBank sequence. The phylogenetic analysis of our cultured parasite based on the 18S gene led us to conclude that this isolate is not related to the genus Perkinsus but to the protists Anurofeca, Ichthyophonus, and Psorospermium, located near the animal-fungal divergence. These last two genera have been included, together with Dermocystidium, in the newly described DRIPs (Dermocystidium, rossete agent, Ichthyophonus, and Psorospermium) clade, recently named Mesomycetozoa., This work was partially funded by the Commission for Cultural, Educational and Scientific Exchange between the United States and Spain.

The genus Dermocystidium is very comprehensive in the host and site of infection, however this is the first report of the occurrence of Dermocystidium sp. in the gills of Nile tilapia. This study was carried out in a fish farming located in the state of Santa Catarina, Brazil. No mortalities were reported in the facility studied and the animals were clinically healthy. During the histopathological analysis of the gills, 8.33% of the fish presented spores of Dermocystidium sp. in the gill tissue. The spores reported herein had a mean length and width of 6.206 x 5.233 μm and a refractile body diameter of 1.965 μm and were studied by histopathology and Transmission Electron Microscopy. This study highlights the importance of a new branchial pathogen in farmed tilapia, as well as to its pathogenic potential, considering the outbreaks of mortalities associated with other fish species.

THE examination and control of oyster (Crassostrea virginica Gmelin) pathogens have received much impetus in recent years with the recognition of Haplosporidium costale Wood and Andrews, ‘MSX’ an undescribed haplosporidian, and Dermocystidium marinum Mackin, Owen and Collier along the Atlantic and Gulf coasts of the United States. Research in the problems of isolation, identification and control of oyster pathogens could bo facilitated if techniques for the culture of oyster cells were available.

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.