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Habitat Assessment & Marine Chemistry Program

Reduced Ability of Parasitized Juvenile Walleye Pollock To Capture Prey

Juvenile walleye pollock (Theragra chalcogramma) harbor the microsporidian parasite Pleistophora sp. encysted in the dorsal musculature. The parasite can infect upwards to 26% of the population of foraging juvenile walleye pollock.

In laboratory tests, juvenile pollock averaging 11 cm in total length had a reduced ability to capture euphausid prey when the fish had more than five of the encysted microsporidians in their flesh. During 50 predator-prey trials, individual juvenile pollock were observed to determine how many euphausids the fish could consume in 3 hours. The musculature of each fish was then examined for the present of cysts, and the number of prey consumed was regressed against the number of detected Pleistophora sp. cysts.

Uninfected walleye pollock were able to consume a mean of 58% of their prey during the allotted time. In contrast, pollock with five cysts were only able to consume 35% of their prey in the same time period.

This ability to capture prey declined with increasing parasite intensity. The juvenile pollock were of similar lengths, and predator size was not significantly correlated with performance in the tests. Infection with the microsporidian parasite has the potential to reduce the foraging ability of juvenile walleye pollock.

By Adam Moles


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