Meet the Northern Cavefish: 2024 USA Cave Animal of the Year
The USA Cave Animal of the Year program enters its fifth year in 2024. This program brings attention to the amazing animals that occur in caves and associated subterranean habitats. Many animals live underground in the thousands of caves in the United States. As cavers, we are the visitors to their domain, and it is good to get to know our hosts a little better. What animal is the focus for 2024?
2024 USA Cave Animal of the Year in 2024: Northern Cavefish (Amblyopsis spelaea)
The Northern Cavefish belongs to the family Amblyopsidae, which includes five other cavefish species endemic to the Ozarks and Interior Low Plateau karst regions in the central and eastern United States. The Amblyopsidae has long intrigued biologists. These fishes have been an important model system for studies of cave adaptation.
What Does a Northern Cavefish Look Like?
The Northern Cavefish was the first stygobiotic (obligate cave-dwelling) fish described in the scientific literature. James DeKay described the cavefish in 1842 based on specimens collected from the River Styx in Mammoth Cave National Park. Northern Cavefish are larger cavefishes reaching up to 12.5 cm (5 in) in length as adults. They lack externally visible eyes and have extremely reduced pigmentation, making them appear white to pinkish white and translucent in life. The head is large and flat with a protruding lower jaw, tubular nostrils, and a series of ridges lined with specialized sensory structures called neuromasts that are part of the lateral line system. The lateral line system is used to detect movement, vibrations, and pressure gradients in the surrounding water to help cavefish detect their surroundings, predators, prey, and each other. The neuromast ridges also occur along the body and caudal (tail) fin. Northern Cavefish have extremely small or lack pelvic fins. Unlike most fishes, the vent (external opening to the reproductive and digestive tracts) of Northern Cavefish and other amblyopsids is positioned in the throat region rather than closer to the caudal fin.
Where Can I Find Northern Cavefish?
The Northern Cavefish is known from several caves in the Pennyroyal Plain of central Kentucky from near the Ohio River southward to the Mammoth Cave System in Breckinridge, Edmonson, Hardin, Hart, and Meade counties. Because Northern Cavefish inhabit subterranean streams that often cannot be completely surveyed, it is likely that the species occurs at other sites, many of which are inaccessible to humans. Two of its known main population clusters are separated by the Rough Creek Fault Zone, which is thought to be a barrier to dispersal.
Northern Cavefish are stygobionts that live in subterranean aquatic habitats including deep pools and shoals in cave streams, smaller tributaries, and rimstone pools. These habitats typically have little to no current, with silt to sand substrates, and abundant organic matter to support their food base. Most sites with Northern Cavefish appear to support small populations; however, a hundred or more have been observed at a few caves during an aquatic survey. The largest populations occur in base-level streams with deep pools and shoals with ledges, overhangs, breakdown boulders, and side channels that serve as refugia during flood conditions. Northern Cavefish co-occur with Southern Cavefish (Typhlichthys subterraneus) in the Mammoth Cave System. However, Southern Cavefish are also found in higher level streams that are drains of vertical shafts, whereas Northern Cavefish only inhabit deeper water at base level further downstream.
What Do Northern Cavefish Eat?
Northern Cavefish are carnivorous and feed on a variety of prey, such as copepods, isopods, amphipods, small crayfishes, and small salamander larvae. Larger adults may even cannibalize smaller cavefish!
How Do Northern Cavefish Reproduce?
Reproduction may be triggered by seasonal flooding of cave systems during late winter and early spring. Females have around 65 eggs per reproductive episode but likely do not reproduce every year. Females in some populations have been observed branchial brooding their eggs. This rare form of parental care in fishes consists of eggs developing and hatching within the protection of the gill cavities. Compared to surface-dwelling fish, Northern Cavefish take a long time to reach sexual maturity (5–10 years) and may live well over a decade, perhaps much longer.
Threats to Northern Cavefish
Populations of Northern Cavefish, like many stygobionts, face several threats. Groundwater pollution is perhaps the most significant stressor potentially impacting the species. This can include a toxic chemical spill, agricultural runoff, and sewage effluent. Land development can alter surface hydrology, which can influence water volume, water velocity, and levels of sediment flowing into karst cave systems. Other threats to Northern Cavefish populations include construction of impoundments on surfaces rivers and streams, pumping of groundwater for agriculture and human consumption, climate change, and potential over-collection of cavefishes for the aquarium trade or scientific purposes. For example, there are reports of Northern Cavefish being sold or given away as a novelty item during the 1800s.
Conservation of Northern Cavefish
Biologists continue to monitor populations through periodic surveys and threat assessments. Some populations occur on properties owned and managed by local, state, or federal agencies (e.g., Mammoth Cave National Park, Fort Knox Army Installation, Otter Creek Outdoor Recreation Area) and are afforded some protection; however, many occur on private lands where their protection is less certain. The Northern Cavefish is considered Imperiled to Vulnerable (G2G3) by NatureServe, as Near Threatened by the International Union for the Conservation of Nature (IUCN), and as Threatened by the American Fisheries Society and Southeastern Fishes Council. A recent 12-month petition finding by the U.S. Fish & Wildlife Service concluded that the Northern Cavefish is not in immediate danger of extinction and does not warrant listing as an endangered or threatened species under the U.S. Endangered Species Act at present.
Why are Cavefishes Important?
Cavefishes are critical components of aquatic subterranean ecosystems, acting as top predators in many cave systems. Protecting cavefishes and their groundwater habitats is crucial for not only preserving subterranean biodiversity but for safeguarding an important resource that we, as humans, are becoming increasingly reliant upon. Cavefishes have been valuable models for scientific research, particularly in the fields of evolutionary biology, ecology, genetics, and developmental biology. The troglomorphic traits and adaptations that cavefishes possess offer unique opportunities to understand how life adapts to extreme and harsh environments. Moreover, cavefishes also have become important models in biomedical research because of their regenerative abilities, genetic adaptations, and resistance to several diseases, such as cancer and diabetes.
How Can You Can Participate?
We need your help spreading the word about Cave Animal of the Year. Please share this website address with friends and on your Grotto social media. If you are lucky enough to find a Northern Cavefish or one of its relatives while caving, help others see it and learn about these cave species. We invite you to take a photo of the cavefish and post it on the USA Cave Animal of the Year Facebook page. In addition, we encourage cavers to report sightings of cavefishes to state biologists that are tracking and studying these species. Have another great year of learning about and helping to conserve habitat for the fascinating animals that make caves their homes!
Dedication to Dr. William D. Pearson
This installment of the Cave Animal of the Year is dedicated to the memory of Dr. William D. Pearson, who passed away in December 2023. Bill was a Professor of Biology at the University of Louisville for 39 years where he taught classes on Ecology, Ichthyology, Fisheries Management, and Biospeleology and mentored 28 graduate students. He and his students surveyed cave aquatic biota including Northern Cavefish. They also developed a cave Index of Biological Integrity. Bill was an excellent scientist, a generous colleague and a caring, affable person. He is missed.
Previous USA Cave Animal of the Year
This is the fifth year for the USA Cave Animal of the Year. The NSS supports this worldwide initiative to bring more attention to the amazing creatures that live underground.
Learn about:
2023 Ceuthophilus Cave Crickets
2021Pseudanothalmus Cave Beetles
2020 Great Basin Cave Pseudoscorpion
Cave Animals of the Year from Other Countries
Several other countries also celebrate Cave Animal of the Year
Germany (Comb-footed Cellar Spider)
Italy (Geotritons-European cave salamanders)
Australia (Nullarbor Blind Cave Spider)
Switzerland (Cave Spider)
USA Cave Animal of the Year Committee
Don Arburn, Gretchen Baker, Dante Fenolio, Kurt L. Helf, Devra Heyer, Jean Krejca, Cait McCann Terán, Shiloh McCollum, Matthew Niemiller, Kara Posso, and Michael Slay.
