Exploring the Underwater World

By John Lyons, University of Wisconsin-Madison Zoological Museum and Dave Marshall, Underwater Habitat Investigations, LLC

Little fish, those under a few inches in length, garner little attention or appreciation. But they play an outsized role in the health of Wisconsin’s lakes.

There are two types of small fish, the juveniles of the panfish and gamefish, who grow quickly and are only small for their first few months, and the inherently small species, which we affectionately term “dickey fish”. These species never exceed a few inches in length. Wisconsin’s lakes collectively support about 30 dickey fish species. Some are quite beautiful and others nondescript, but all are important.

Although easy to miss, dickey fish are essential players in the food web. They eat algae, tiny invertebrates, and the detritus from decayed plants and animals. In turn, they are eaten by larger fish, especially carnivorous species like crappie, bass, catfish, pike, musky, perch, and walleye. Dickey fish are the link between aquatic plants and the gamefish that so many of us love to catch. A healthy sport fishery requires a healthy dickey fish community.

Most dickey fish are found among aquatic plants where they hide from predators, eat the algae and invertebrates the plants support, and lay their eggs on the leaves and stems. Unsurprisingly, when native aquatic plants decline, so do dickey fish. And when native plants are displaced by non-native species such as Eurasian watermilfoil or curly leaf pondweed, dickey fish suffer. The native plants provide much better habitat.

Over 150 years ago, Wisconsin’s lakes were full of small, plant-loving fish living among native underwater plants. Today, those fish are much harder to find. In Lake Mendota in Madison, for example, there were once 10 dickey fish species, but now only two remain and neither is common. While we don’t have as much long-term data for every lake, similar declines are happening across the state.

Much of this change can be directly linked to human impacts. The introduction of common carp, runoff from soil erosion and fertilizers, and harmful blue-green algae blooms have all taken a toll. Shoreline development has also reduced important plant habitat, and invasive species like Eurasian watermilfoil have spread. Even some well-intended efforts to control invasive plants can sometimes remove too much of the good habitat these fish depend on. Together, these changes have made it harder for these once-common fish to thrive.

Many lakes probably still have a few dickey fish, and gamefish should still have a species or two to eat. So, why should we worry?

The issue is what’s called “redundancy” in ecological terms and “having a backup plan” in everyday life. Basically, the more species you have, the less likely you’ll have a year when all dickey fish are scarce and gamefish go hungry. The abundance of each dickey fish species fluctuates dramatically from year to year. Often these fluctuations are in synch, good or bad, but when you have lots of species, there will be one or two that will do well when the others do poorly, and consequently there will always be enough food for gamefish. But when the variety of dickey fish is low, the chances rise that all species will have a bad year together and gamefish won’t have enough to eat.

It’s like having a balanced investment portfolio; diversity makes it more resilient when things don’t go as planned. Similarly, if there are only one or two dickey fish species, the food base is at risk of collapse when conditions aren’t favorable. With many dickey fish species, the lake ecosystem can better ride out the occasional tough times.

Do you know what kind of dickey fish are in your lake? Most lakes don’t have adequate data even though it only takes a couple of days to conduct a survey. And as fish biologists, we strongly recommend it. Find your local WDNR fisheries biologist.

If you know there are a good variety of dickey fish in your lake, conservation is key. Protect the water quality and habitat, especially the aquatic plants that are essential for dickey fish to thrive. If a fish survey reveals no or just a few species, your lake community could explore restoration. Helping these fish make a comeback often starts with improving water quality and habitat, especially aquatic plants. But this alone may not be enough. Dickey fish can’t easily move from one lake to another, so even if conditions improve, they may not re-establish on their own. The good news is that restoration is still possible. Although the process is complex, projects throughout the Midwest, including Wisconsin, show that dickey fish can be successfully re-introduced through stocking.

While dickey fish are small and inconspicuous, these fish are key to a healthy lake ecosystem, and losing them could have perilous consequences!

Where did the name “dickey fish” originate? Biologists sometimes use the slang term “dickey” to refer to small, visually non-descript species, most commonly among birds and non-game fish. This dates back to 18th century English when the nickname Dicky was often used as a pet name for small animals, and a nursery rhyme popularized calling small, common yard birds “dicky birds”.

Iowa Darter (age 8+)
Freshwater Fish Series, Volume 2

Learn how these native Wisconsin fish grow, where they like to hang out, and what you can do to keep their waters healthy.

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