Beneath the Surface: Unraveling the Story of a Mysterious Water Find

By Emily Heald, Extension Rivers Educator

I often say to people, “If you find something in the water that you can’t identify, send me a photo. If I don’t know what it is, I bet I know someone who does.”  I love helping folks learn about the things they see in the water! Plus, folks tend to become stewards of the resources they are interested in and care about.

I can often identify most pictures I receive, but I had one recently that left me stumped:

A mysterious, pale white rubbery object that has seven short tentacles and a long tail. The mystery find lays on the pebbly surface of a lake or stream bed under shallow, clear water. It appears to be about 2-3 inches long.
Mystery photo by Katelin Anderson, Polk County Land and Water Resources Department

….and I was truly perplexed. I had a few immediate ideas: a yet-to-be-discovered, giant hydra; perhaps the parasitic alien from the movie Alien; or my best guess – fish guts of some sort. I asked a few colleagues, and everyone was as stumped as I was. One of my former coworkers, Licia Johnson at North Lakeland Discovery Center, said she had no idea what the image was, but that she found something similar on the shoreline of Lake Superior recently:

A mysterious, pale white rubbery object sitting on a rock, that has a round part attached to more than 15 short tentacles. It appears to be about 3 to 5 inches long.
Second mystery photo found on the Lake Superior shoreline by Licia Johnson, North Lakeland Discovery Center

It left me even more baffled. Finally, I found the answer from John Lyons.

John has several excellent professional titles, including Curator of Fishes for the University of Wisconsin Zoological Museum, Academic Lecturer for UW-Madison, Affiliate Scientist for UW-Madison Center for Limnology, and Retired Fisheries Research Scientist and Supervisor for the Wisconsin DNR.

John quickly identified these fleshy mysteries as the stomach and pyloric caeca (“see-kuh”) from a fish.

What are pyloric caeca?

Pyloric caeca are finger-like structures found in many fish species, located at the junction of the stomach and the intestines. The number of caeca can vary hugely depending on the species.

John said the finding from Polk County “could be from a walleye, which has 5-9 caeca, and the one from Lake Superior could be from a smallmouth bass, which has 25-30 caeca. Whitefish, trout and salmon have many more caeca than these two, ranging from 50-250 caeca, and the number of pyloric caeca is often used to help in identification. But for most other species, they are not needed for identification.”

What are they for?

Fascinating! So, what is the purpose of these alien-like structures? They are key for digestion. In general, the caeca help to increase surface area, which helps with nutrient absorption, and therefore more efficient processing of nutrients. Pyloric caeca are most commonly found in carnivorous fish that need help breaking down complex proteins.

Find anything mysterious in the water lately? Send a photo to wav@extension.wisc.edu for your chance to be featured in our next newsletter!