Whitefish (C. nelsonii) has Brown Skin

Observation: A whitefish (Coregonus nelsonii) was caught on the Kuskokwim River near Bethel in a 4 1/2 in net that was set under the ice. The fish has a brownish moldy growth all over its body. We would like to know more about what is going on with our fish and why this is happening to our fish so we can become more aware of any dangers associated with this kind of sickness.

LEO says: In late November, there was a story in the Nome Nugget about tom-cod with black spots on their skin. We posted the story on the Northern Climate Observer (NCO) ADF&G fishery biologists speculate that the tom-cod lesions were a black mold, like the kind commonly found in houses. The fact that a land based fungus is appearing in fish, is one reason why ADF&G is following reports of this fish illness and has requested help with local observations and samples. (November 27, 2014)

Alaska Department of Fish and Game Consult: Jayde Ferguson, Fish Pathologist writes, "here is a link to our fish disease book and attached are documents on the black fungus that we are investigating and information regarding Alaskan whitefish. Dr. Coggins sent me additional photos and the fungal-like lesions are consistent with Saprolegnia or a related species. As the growth in these lesions age, they accumulate detritus and algae and appear brownish in color, as seen in the photos. Unfortunately the fish was frozen so no meaningful tests can be performed. However, the photos were convincing that this represents a Saprolegnia-like organism. Information on Saprolegnia can be found in the fish disease book, pages 34-35. Basically these are decomposers that are ever-present in the environment and commonly infest fish that have received physical trauma. It is also very common in salmonids during spawning season and my understanding is that whitefish in your area are still spawning. Although whitefish do not break down and die after spawning like Pacific salmon, their immune system and body condition is reduced during spawning and causes them to be susceptible to organisms in the water. There is no human health concern for Saprolegnia in fish. "As far as future observations about fish like this one, Dr. Ferguson writes: "The first step to take would be to contact the lab. Photographs can be helpful to obtain a preliminary diagnosis, which helps filter through other common diseases such as the saprolegniasis (Saprolegnia) that was determined in this case. If the lesion is consistent with the black fungus of interest, then fresh (not frozen) material could be sent and this should be coordinated with the lab. At that point, we can provide more detailed instructions of how to package the fish, forms to fill out, etc. ADF&G can pay for shipping costs."