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Fisheries Resources Pathobiology - Active Research

Steller Sea Lion Parasitology
Recently, the Team has directed effort at attempting to understand the role that disease and parasitism may have had on the decline of the Steller sea lion (SSL) (Eumatopius jubatus). Of equal, but of more proximal importance, the Team is conducting research on how disease and parasitism may delay recovery of this endangered species. In general, the Team is contrasting parasite ecology in prey around selected SSL rookeries and comparing parasitic fauna and densities of the SSL between rookeries. Preliminary evidence suggests that parasite ecology around rookeries are similar, but that parasite prevalence and densities in SSL may vary between rookeries. In addition, new evidence indicates that the hookworm, Uncinaria sp. may affect pup health and survival. This revelation is critical as it appears that increased pup and juvenile mortalities are a major cause for recruitment failure in recent years.

Bitter Crab Syndrome
Heavy Hematodinium infection in the eye stalk of  the snow crab, Chionoecetes opilio. Bitter Crab Syndrome (BCS) is a 100% fatal disease of North Pacific Chionoecetes crabs that is caused by an undescribed parasitic dinoflagellate of the genus Hematodinium. First identified because of a very bitter taste imparted to large heavily infected cooked crabs, current data indicates that the disease is not a public health concern. Although, the method of infection and the complete life history of the parasite is is not known, various stages of the dinoflagellate are evident. Two such stages are shown in the photograph above (cellular-level of a snow crab, Chionoecetes opilio, eyestalk), pre-spore stages and vegetative stages. Note the darker nucleus of the pre-spore stages as opposed to the larger nucleus and foamy cytoplasm of the vegetative stage. Our data indicate that small crabs are more susceptible to infection than large crabs which could affect recruitment. The Team continues to monitor the prevalence and distribution of BCS in North Pacific crabs and is developing tools to more accurately detect BCS in affected populations. Molecular tools will be employed to identify the parasite and compare it with known similar parasites in other crustaceans worldwide.

Juvenile Walleye Pollock
A heavy but focal microsporidian, Pleistophora sp., infection (asterisk) in the muscle of  juvenile walleye pollock. Walleye pollock (Theragra chalcogramma) are a major North Pacific fishery which experiences population fluctuations. In nature, the causes of many of these episodes are unknown and probably complicated. For 15 years, the Team has investigated the diseases of juvenile walleye pollock as a means of attempting to understand how disease affects recruitment. Several parasites and diseases have been identified, but only a microsporidan infection appears important. The undescribed microsporidan (Pleistophora sp.), indicated by the asterisk in the photograph at right, infects the skeletal muscle of both juveniles and adults with likely different effects. In juvenile walleye pollock, mortalities are possible but it is more likely that affected fish will have increased difficulty in capturing prey or evading predators. In adults, Pleistophora is likley to affect fecundity. Future research is being planned to more accurately monitor the parasite in walleye pollock populations and to characterize the parasite at the molecular level.

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