Black Patches on Cisco fish (Coregonus autumnalis) appear to be Phaeohyphomycosis

Observation by Patrick Tam:

I caught a cisco fish (imarpinraq in Yup'ik Eskimo) in my net in the Yukon River set about halfway between the villages of Emmonak and Alakanuk. The fish had black patches on its body that looked like some kind of infection. I took 2 pictures but left the fish on the ice.

Follow up (3/24/21): Thank you for the information on the fungus. I left the fish for the foxes and ravens. When I returned to the net a couple of days later, the fish was gone so retrieving a sample was not possible.

Jayde Ferguson, Fish Pathologist with the Alaska Department of Fish and Game, writes:

Yep, that does look to be the same fungal syndrome as previously reported [in Kipnuk]. Here is a link to a new chapter in our booklet regarding this condition.

The sample is probably in too poor of condition to look at now. Ideally we’d like these samples fresh, not frozen, which is difficult to maintain once they’ve been taken out of water on the ice. If an optimal sample is encountered in the future, then we’d be interested in examining it because we’ve found several species involved and thus it’s a syndrome. Would be good to get material from viable fungus in these cases to continue to identify the fungal species involved.

Comment from LEO Editors:

Two other LEO members have submitted observations of phaeohyphomycosis infections in fish. In November of 2015, Nick Slim reported that smelt caught near the mouth of the Kugkaktlik River, about ten miles downriver from the village of Kipnuk, had unusual black spots on their skin. In May of 2018, Mary Matthias reported similar black markings on smelt caught bear Bethel. In both these cases, these spots were identified as the fungal infection phaeohyphomycosis, and residents were advised not to eat the fish.

According to the report that Jayde shared, called "Phaeohyphomycoses of Saffron Cod and Possibly Other Fish Species", There are at least 8 kinds of fungi identified that cause these black spots. Research suggests the fungus infects fish through a wound by entering the surface of the skin and invades the underlying skeletal muscle. The actual mode of transmission is unknown, but they are likely caused by ascospores contained in ambient sea water and sediment.

Mortality rates for infected fish are approximately 1 in 200. Previous cases have appeared on saffron cod (leginus gracilis), and rainbow smelt (Osmerus mordax) from Norton Sound in the late fall and early winter months. The fungi are found on paper products, wood, natural fiber textiles. One strain (chaetomium globosum) produces mycotoxins and commonly grows inside homes on water damaged roofs, ceilings, walls and carpets and which can be a source of allergies for humans. Chyna Williams