Black eye syndrome and a systemic rickettsia-like organism in Alaskan Chionoecetes spp. crabs, including normal eyestalk microanatomy

Jul 28, 2022Diseases of aquatic organisms

Black Eye Syndrome and a Rickettsia-Like Infection in Alaskan Snow Crabs, Including Normal Eye Structure

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Abstract

Prevalence of black eye syndrome (BES) in Alaskan snow crabs ranged from 0.37% to 19.6% depending on the sample.

BES was identified in both captive and wild populations of snow crabs and Tanner crabs in Alaska.
Two distinct manifestations of BES were observed: abnormal black eye pigmentation without histological lesions and corneal shell disease with ulceration.
The initial abnormal pigmentation appears to be noninfectious and may be linked to changing ocean conditions affecting crab biology.
Potential damage to crab eyes from light exposure might contribute to early signs of pigmentation changes.
A previously unreported rickettsia-like organism was found in some dead snow crabs but was determined to be unrelated to BES.

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A black eye syndrome (BES) was discovered in both captive and wild populations of Alaskan snow crabs Chionoecetes opilio and Tanner crabs C. bairdi. Field prevalences ranged from 0.37% (n = 594/161295) to 19.6% (n = 62/316) in snow crabs from the eastern Bering Sea and from 0.09% (n = 15/16638) to 0.7% (n = 133/18473) in Tanner crabs from the same trawl samples, with a slightly greater percentage (1.4%, n = 57/3945) in Tanner crabs from the Aleutian and Kodiak islands fisheries in the Gulf of Alaska. BES is not associated with crab mortality and has 2 distinct manifestations: abnormal black foci of internal eye pigment with no discernible histological lesions, which, in many cases, is followed by corneal shell disease with ulceration and distal eyestalk erosion. It is assumed for this study that these are early and late stages of BES that are somehow related. Our results suggest that early stages of abnormal pigmentation are noninfectious, possibly related to changing ocean conditions affecting crab endocrinology and neuropeptide control of secondary eye pigment. Potential light-induced photoreceptor damage of harvested crabs with dark-adapted eyes is another anthropogenic factor possibly contributing to the early changes in eye pigmentation. Normal eyestalk microanatomy specific for Chionoecetes spp. is provided as necessary baseline information for future studies. Early in the study, an unreported rickettsia-like organism (RLO) was discovered infecting dissected black eyestalks submitted for examination from 5 of 6 dead snow crabs, suggesting association with BES. Subsequent samples indicated the RLO was systemic, infected both black and normal-appearing eyestalks, and was unrelated to BES. However, the multiorgan infection and histopathology indicated the RLO could be a primary pathogen of snow crabs.

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