Students Solve Case of the ‘Mystery Fish’ on UW-Madison Fieldtrip

Electrofishing crews collecting fish from a riffle in Badger Mill Creek. Photo: C. Gottschalk Druschke

by Rob Mooney – Spring is always a busy time for people that study freshwater ecosystems in the Midwest – lakes begin to thaw, streams rise after the snow melts, and many species of fishes start to migrate and spawn. For the students in the Ecology of Fishes lab (Zoology 511 for any interested undergrads) at the University of Wisconsin-Madison, it brings the highlight of the course – the Badger Mill Creek field trip!        

Students using a dichotomus key to identify specimens they just received from the electrofishing crew. Photo credit: Rob Mooney

In the weeks before the fieldtrip, when spring semester is starting and the ground is (usually) still covered in snow, ZOO 511 students spend countless hours learning how to use external anatomy to identify fish. Whether it is knowing the scale patterns on the cheeks of northern pike and musky, the best way to distinguish a fathead minnow from a bluntnose minnow, or that Johnny Darters have unique ‘X’ and ‘Y’ shaped blotches on their sides, the students in ZOO 511 learn the distinguishing characteristics of common fishes in the Midwest. Eventually, they’re able to tell what family and genus a certain specimen belongs to all the way down to the individual species. This not an easy task, especially for certain fish families. Cyprinids, or minnows, for example, are notoriously hard to identify and differentiate, but having that skill allows people to distinguish a non-native goldfish from native minnows or native suckers – which came in handy during this year’s field trip! But after learning the characteristics of fishes and how to use dichotomous keys to identify fish, students get the chance to collect live specimens and put their skills to the test.

Students electrofishing an undercut bank in Badger Mill Creek. Photo: Rob Mooney

Every spring, the ZOO 511 class heads to Badger Mill Creek with waders, backpack electrofishers, and nets to embark on what is usually their first field experience in fish ecology. Students use electrofishers as a way to non-lethally stun and collect fish and then identify, measure, and safely release them. This field trip gives them the opportunity to not only collect fish and test their identification skills, but also relate fish morphology to fish ecology.

Notice the enlarged pectoral fins on this mottled sculpin. Photo: Karissa Lange

I’ve been a teaching assistant for the Ecology of Fishes course for the last three years and it’s always rewarding to see students take what they’ve learned in the lab and use it in the field. For example, when students see the large pectoral fins on a sculpin, it suddenly clicks that those fish use their large fins as a “sail” to cling to the streambed and the concept of form and function hits home. This year, students waded into the chilly stream and began waving the wands of their electrofishing backpacks through the water. The jolt of electricity temporarily stuns fish near the surface of the water, where students scoop them into their nets. Following collection, the fish were handed to over to another group of students for processing. This includes identifying the fish and determining its length and weight, along with recording the data – which they use later in the semester to write a lab report in the style of a scientific paper. This year we caught brown and rainbow trout, multiple species of native minnows, darters, and one little mystery – a plump, large-scaled specimen that turned out to be a huge non-native goldfish! (Editor’s Note: PLEASE don’t release pet fish!)

This goldfish was quite the surprise when it was collected from a pool along with brown trout! Photo: Rob Mooney

Most of the students had never seen a large goldfish in the wild before (they can look quite different from goldfish children have in fish bowls), so knowing external anatomy and being able to use a dichotomus key were skills needed to identify the specimen. The single, saw-toothed dorsal spine and lack of barbels on its lip led the students to successfully identify it as a goldfish.

            At the end of the course, we want students to leave with the ability to safely collect and measure fish, identify them to species, and relate fish morphology to ecology – all of which are highly-valuable skills in any fish-based, ecological career. Hands-on experience is critical for early-career ecologists and scientists, and if this year’s class is any indication – our students are primed for fishy careers!

A brown trout returned safely to the stream. Photo:m Rob Mooney