A biological and taxonomic study of selected myxosporida of some Oregon fresh-water fishes Public Deposited



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  • Biological studies were conducted on a histozoic myxosporidan Myxobolus insidiosus (Wyatt and Pratt, 1963) from the musculature of Oncorhynchus tshawytscha (Walbaum). This organism is known to occur in spring chinook salmon in Oregon and coho salmon O. kisutch (Walbaum) in Washington. In addition Myxobolus kisutchi (Yasutake and Wood, 1957) was found in cysts in the brain of a new host, the spring chinook salmon. Salmo clarki clarki (Richardson) was found to be parasitized by a Myxobolus sp. The spore morphology and the location of some cysts in the connective tissue of the striated muscle differ from that of M. insidiosus. Transmission studies on Myxobolus insidiosus in disease free water supplies provided only negative data. Infected tissue from juvenile and adult fish fed to susceptible juvenile salmon failed to produce disease. Contact of non-infected juvenile fish with infected juvenile salmon also failed to produce disease. Uninfected, juvenile fish, continuously exposed to spore-seeded mud for 210 days failed to develop the infection. Mud from an infective area in running spring water was not infective to susceptible fish. Fish placed in rearing ponds receiving water in which fish previously had developed the infection became diseased. Experiments with fish infected in this way provided positive data. The time between exposure to infective water and finding of patent disease was between 76 and 83 days. The disease becomes patent when the average daily water temperature is near 8.4°C. Fish exposed to infective water for a period of eight to 22 days became infected. If the exposure was in February and March, increases in exposure time raised the percent of infection, but similar periods of exposure in May resulted in a reduced incidence of the disease. Data indicate that the McKenzie River water is probably not continuously infective. Placement of fish with the prepatent disease in warmer water caused the disease to become patent and accelerated the time to spore formation. Susceptibility was not dependent on age or size of fish. Spores were found in adult fish that had returned to spawn after four years at sea. Transmission of the disease on or in the egg does not appear to take place. There was a 12.5 percent disease incidence in fish reared in concrete raceway ponds. Fish from dirt rearing ponds which were in series had a 100 percent incidence at the time of liberation. Water turnover rate is important in the epidemiology of the disease. Calcium hydroxide at 0.12 and 0.25 percent caused apparent degeneration of the spores when tested in mud after 216 hours of exposure. Spores in mud with water flowing near them may remain morphologically intact up to 298 days. The nitrofuran drug, Furanace, was ineffective against trophozoites of Chloromyxym sp. and vegetative stages of Myxobolus insidiosus. A diagnosis of Myxobolus insidiosus in juvenile and adult coho salmon in the Lewis River in Washington was confirmed. Autoinfection of juvenile spring chinook with M. insidiosus could not be confirmed. Compact nodular areas made up of fibroblasts and mesenchymal-like cells were found in areas of striated muscle where spore-bearing cysts once occurred.
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  • description.provenance : Approved for entry into archive by Katy Davis(kdscannerosu@gmail.com) on 2014-01-29T19:14:53Z (GMT) No. of bitstreams: 1 WyattEllisJ1972.pdf: 2854723 bytes, checksum: 15a9c8df8426f6aaac95184b9d3614d2 (MD5)
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