Check Out the Checkered Sculpin

By Emma Brentjens, NCRN I&M Science Communications Intern

The checkered sculpin is the most common fish species in Antietam National Battlefield’s Sharpsburg Creek.

USFWS / Ryan Hagerty

A New Species

Deep in the cool headwater streams of the Potomac River lives a small, bottom-dwelling fish, hardly bigger than your index finger, called the checkered sculpin (Cottus sp.). It sports a checkerboard-like pattern on its sides and is known to live in only a few limestone-influenced streams in Maryland, Pennsylvania, Virginia, and West Virginia. (And one of those streams is Sharpsburg Creek at Antietam National Battlefield!)

For years checkered sculpin lived largely unnoticed, mistaken for their similar-looking and more widespread cousins, the slimy sculpin (Cottus cognatus). In recent decades however, it was confirmed checkered sculpin are a physically and genetically unique species. Here’s what to know about these fascinating fish.

Checkered sculpin have a distinct checkerboard pattern on their side.

Matt Tillett / Maryland Biodiversity Project

Adult slimy sculpin.

U.S. National Park Service

It’s a Fish-Eat-Fish World 

Small fish like checkered sculpins are often eaten by larger fish. So much so that a popular fly-fishing lure called a “muddler minnow” attracts game fish by imitating a sculpin. However, sculpin can and do eat very young game fish, like trout, when the trout are small. According to ichthyologist (fish scientist) Dr. Richard Raesly, “in the aquatic realm, if it fits in your mouth, it's food.” 

The Sculpin Family: Fin-ding Long-Lost Relatives

The checkered sculpin is one of the approximately 100 Northern Hemisphere sculpin species that live in freshwater. The rest (worldwide there are an estimated 250-300 known sculpin species in genus Cottus), live in the ocean. Dr. Richard Raesly at Frostburg State University who has studied sculpin for decades, believes that there are far more of these freshwater sculpin species than we think.

Freshwater Sculpin Found in National Capital Region Parks

• Checkered sculpin (Cottus sp.): Antietam National Battlefield
• Blue Ridge sculpin (Cottus caeruleomentum): Catoctin Mountain Park, C&O Canal National Historical Park, and Monocacy National Battlefield
• Potomac sculpin (Cottus girardi): C&O Canal National Historical Park, George Washington Memorial Parkway, and Monocacy National Battlefield
• Slimy sculpin (Cottus cognatus): None. The slimy sculpin once documented at Antietam have since been identified as checkered sculpin!

Sculpin species found in National Capital Region national parks: Checkered sculpin

© Emilio Concari (CC BY-NC) / Maryland Biodiversity Project

Potomac sculpin

Emilio Concari (CC BY-NC) / Maryland Biodiversity Project

Blue Ridge sculpin

Emilio Concari (CC BY-NC) / Maryland Biodiversity Project

While studying their movement in Maryland streams, Raesly found that freshwater sculpin tend to stay put in one place. In fact, they may move less than two meters over multiple years! One Blue Ridge sculpin, he recalled, was captured multiple times at the same sampling area. This lack of movement, Raesly explained, reduces the flow of genes between different sculpin populations, and can lead to the development of distinct species. This is likely how the checkered sculpin came to be.

Checkered sculpin have three pelvic fin rays. Other sculpin, like the Potomac sculpin and mottled sculpin have four pelvic fin rays.

Emilio Concari (CC BY-NC) / Maryland Biodiversity Project, annotated

Raesly first noticed in 1989 that the sculpin he was seeing in Maryland were different. Sculpin are generally distinguished by their color pattern, the number of pores on their chin, and the number of finger-like rays on their pelvic fins (the small fins on their bellies). Checkered sculpin were originally considered a type of slimy sculpin, which live in a large range of Potomac headwater streams, simply because they both have three pelvic fin rays (most North American sculpin have four). However, the fish Raesly was finding had a distinct color pattern and only one pore at the tip of its chin, while slimy sculpin typically have two pores.

Raesly and his students conducted genetic testing and confirmed that the checkered sculpin are a separate species. They are actually more closely related to Potomac sculpin, with which they have an overlapping range. It’s still a new enough “discovery” that the written physical description needed for official species recognition is not yet complete (hence it’s placeholder name, Cottus sp.).

Checkered sculpin have one pore at the tip of their chin (median chin pore).

Emilio Concari (CC BY-NC) / Maryland Biodiversity Project, cropped and annotated

Slimy sculpin have two median chin pores.

U.S. National Park Service, annotated

Checkered sculpin fun fact: World’s best dad?

Male checkered sculpin are highly territorial. They defend their nests—made in rock cavities—protecting their eggs and keeping the habitat clean of debris. 

Keeping Cool

Checkered sculpin are very particular about their habitat. They only live in cold waters that are below 20° Celsius or 68° Fahrenheit. For this reason, scientists consider them an indicator species. Streams with checkered sculpin tend to also have healthy water quality. In Antietam’s Sharpsburg Creek, for example, monitoring of fish communities indicates good stream health, and checkered sculpin have consistently been the most abundant fish species recorded.

The Maryland streams occupied by checkered sculpin have remained fairly stable over time, thanks to cool groundwater inputs from aquifers under the Shenandoah Valley and other parts of the Great Appalachian Valley. Recently though, climate change and groundwater withdrawals for agriculture and urban development threaten that stability.

Because of their small, fragmented range and the threats they face, the checkered sculpin is considered a Species of Greatest Conservation Need by the Maryland Department of Natural Resources.

While checkered sculpin are still thriving at Sharpsburg Creek and the water temperature remains within the acceptable temperature values, continued monitoring helps track how checkered sculpin are faring and helps park resource managers continue to protect this species.

A handful of checkered sculpin

Jeremy Cox / Chesapeake Bay Journal

Fish Monitoring in the NCR

The National Capital Region Inventory & Monitoring Network (NCRN I&M) monitors fish and macroinvertebrates at 37 stream sites in ten parks, including in Sharpsburg Creek at Antietam National Battlefield. Monitoring aquatic organisms helps reveal population trends for species like the checkered sculpin and also provides information about the health of the whole stream.

Further Reading

• Cox, Jeremy. 2022. Among the ‘last cold places,’ a fish defies climate change. Chesapeake Bay Journal.
• Daw, Sonya. 2021. Sculpins.
• Hitt, N.P., Kessler, K.G., Macmillan, H.E., Rogers, K.M. and Raesly, R.L., 2021. Comparative morphology of freshwater sculpin inhabiting different environmental conditions in the Chesapeake Bay headwaters. Environmental Biology of Fishes, 104:309-324.
• Nortrup, Megan. 2015. National Capital Region Network Resource Brief: Fish, Antietam National Battlefield.