Black Spot Gill Syndrome in the Northern Shrimp, Pandalus borealis, caused by the parasitic ciliate Synophrya sp.

•Black spot gill syndrome in Pandalus borealis is caused by the apostome ciliate Synophrya sp.•The ciliate infects the gill tissues and undergoes metamorphosis into histotrophic life stages.•Parasitization by Synophrya sp. leads to the formation of melanized nodules and the distinct gross pathology.•Synophrya sp. epizootics could contribute to decline of P. borealis in North Atlantic commercial fisheries.