CNIDARIA Ceratonova (Ceratomyxa) shasta

I. Causative Agent and Disease absent in parasitized wild fish nor has The parasite Ceratonova shasta is the parasite been found in any hatchery not a protozoan but a metazoan in the stocks of Alaskan salmonids. class Myxosporea in the phylum Cni- daria (anemones, jellyfish, corals) based III. Clinical Signs on molecular studies and the feature of Parasitized fish typically appear discharging cells (cnidocytes) known as darkened in color with swollen or hem- polar capsules. The parasite produces orrhaged vents and abdomens distended crescent shaped spores 14-23 um long by ascites. Although lesions are variable by 6-8 um wide at the suture line. A by age and fish species, the entire diges- single spore contains two refractile polar tive tract may be affected with granu- capsules, each with an extensible coiled lomas and abscesses (boils) causing filament. Vegetative trophozoites and tissue necrosis that may spread to major spores produce necrotic lesions within visceral organs and skeletal muscula- various tissues of salmonid fishes but the ture. These lesions contain developing parasite has a tropism for the gastroin- multicellular trophozoites and spores. testinal tract, especially the intestine. Each trophozoite forms a pansporoblast High mortality may occur in susceptible usually containing two spores. juvenile fish and the parasite contributes to significant pre-spawning mortality IV. Transmission of infected adult salmon. Depending Ceratonova shasta is transmitted on the host species and stock, natural to fish through the gills by infectious exposure to the parasite may allow some actinosporean tetractinomyxon stages fish populations to develop resistance in the water that are shed by parasitized to infection and severity of the disease. freshwater polychaete worms of the Ceratonova occurs seasonally (May to species Manayunkia speciosa that serve November) becoming more intense when as the alternate host. The worms become water temperatures reach or exceed parasitized by ingestion of mature spores 10°C. released by parasitized live or decom- posing fish hosts. However, unlike other II. Host Species myxozoans, the parasite develops within This organism parasitizes several the alternate host epidermis rather than different species of freshwater and ana- within the intestinal epithelium. dromous salmonids and is restricted to the Pacific Northwest (PNW) and British V. Diagnosis Columbia. Ceratonova shasta is present Tissue lesions or intestinal scrapes in wild adult chum, coho and sockeye are examined for spores having the typi- salmon, rainbow trout and Dolly Varden cal size and morphology of this parasite. in Alaska within several south central Identity is confirmed with fluorescein or and interior drainages including; Yetna, enzyme conjugated antibody tests and Yukon, Naknek, Wood, King Salmon, by PCR specific for Ceratonova shasta. Togiak and Sushana Rivers and Lower Talarik, Mortenson and Russell Creeks. VI. Prognosis for Host Clinical signs of disease, except for Depending on the fish species, stock white gill nodules in sockeye, have been and water temperature, prognosis may

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be poor with high fish mortality. Major parasite is the only effective method of epizootics of juvenile salmonids in PNW control. hatcheries have commonly occurred when exposed to surface waters where VII. Human Health Signifcance the parasite is enzootic. Resistant fish Although parasitized fish tissues may in enzootic areas can become subclini- be aesthetically displeasing, there are no cal carriers of Ceratonova shasta with human health concerns with Ceratonova spores occurring in the lower intestinal shasta. tract. Prevention of exposure to the

10 um Wet mount of Ceratonova shasta spore with two  polar capsules.

Stained spore of Ceratonova shasta showing polar capsules (arrow) and the medial suture line, X 1000.

Coho salmon with swollen prolapsed vent due to the parasite Ceratonova shasta (photo: R. Holt, Oregon Dept. of Fish and Wildlife).

Bloating due to ascites in fsh parasitized with Ceratonova shasta (photo: R. Holt, Oregon Dept. of Fish and Wildlife).

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