Quantifying Ichthyophonus prevalence and load in Pacific halibut (Hippoglossus stenolepis) in Cook Inlet, Alaska
Ichthyophonus, a non-specific fungus-like protozoan fish parasite, has caused epizootic events among economically important fish stocks including herring and salmon and can result in reduced growth, stamina, and overall fish health. Recently Ichthyophonus was detected in Pacific Halibut (Hippoglossus stenolepis) in Cook Inlet, Prince William Sound, Gulf of Alaska, and the Bering Sea. During the summers of 2012 and 2013 I sampled sex, length, age, diet composition, heart, spleen, liver, and kidney tissues from 563 halibut (364 females, 199 males) landed by the Homer sport-charter fishery using the “pre-dumpster, post-mortem” method. Ichthyophonus prevalence was determined by MEM culture and parasite load (schizonts/ gram) was determined using pepsin digestion. In 2012, 23% of the fish sampled had Ichthyophonus; 29% in 2013. We found no evidence of the parasite in liver, spleen, or kidney tissues and there was no difference in prevalence between males and females. Pepsin digestion analysis indicates a wide range of parasite load among infected fish with 6 to 1,245 Ichthyophonus schizonts per gram of heart tissue. Analyses to determine the diet composition of sick fish using gut contents and stable isotopes are ongoing.
Funding for this work was provided by the Pollock Conservation Cooperative via the Alaska Education Tax Credit Program.
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