Cave Fish: 200+ Species, Why They Lose Their Eyes

Cave fish are fish that live permanently in caves and underground water, and most have lost their eyes and colour. Wikipedia counts more than 200 described obligate cave species, up from about 50 in the early 1990s and about 170 in 2010, and expects the final total to be around 250. They come from more than 25 different families, so they are not one group: cave life has turned many unrelated fish pale and blind independently.

Where they live, by Wikipedia's counts:

• Asia: more than 120 species, including more than 80 in China
• South America: more than 30, including more than 20 in Brazil
• North America: about 30; the US, Mexico, India and Thailand each have 9 to 14
• Africa 9, Oceania 5, Europe 1

Mostly to save energy. Eyes and the brain tissue that processes vision are expensive to run. A 2015 study in Science Advances, led by Damian Moran and reported by Science News, measured this in the Mexican tetra: vision takes about 15 percent of a 1-gram young fish's resting energy budget and about 5 percent in an 8.5-gram fish. In a dark cave with little food, fish that do not pay that cost have an advantage.

The eyes do not simply fail to form. In the Mexican cave tetra, embryos start growing eyes, which break down by about day five and are covered over by skin; BrainFacts reports that dozens of eye-development genes are switched off by methylation. At the same time, cave fish gain stronger taste, smell and motion-sensing (BrainFacts). More on this species on our Astyanax mexicanus page.

Many unrelated kinds. Wikipedia lists cyprinids (the carp family), characins, loaches, catfish, swamp eels and the North American cavefish family Amblyopsidae among the groups with cave species. Some examples:

• Mexican tetra (Astyanax mexicanus): at least 29 blind cave populations in Mexico (Journal of Experimental Biology, 2020); the most studied cave fish (Wikipedia)
• Northern cavefish (Amblyopsis spelaea): grows to about 5 inches, lives well over a decade, and females brood about 65 eggs inside their gill chambers; it takes 5 to 10 years to mature (National Speleological Society)
• Southern cavefish (Typhlichthys subterraneus): another US species (National Speleological Society)
• Alabama cavefish (Speoplatyrhinus poulsoni): see below
• Garra andruzzii: a cave fish whose body clock runs on a 47-hour cycle (Wikipedia)
• Phreatobius cisternarum: a small catfish recorded surviving a year without food (Wikipedia)

Neolissochilus pnar, a mahseer relative from Meghalaya in northeast India. It lives in Krem Um Ladaw and nearby caves; the type specimen measures 329.2 mm, and the largest individual observed exceeded 400 mm standard length (about 16 inches), making it the largest known underground fish. It was photographed and collected in 2019 and formally described in 2023 in Vertebrate Zoology; the name honours the Pnar people of Meghalaya (Wikipedia). Most other cave fish are 2 to 13 cm; the next largest are two Ophisternon swamp eels at 32 to 36 cm (Wikipedia).

None of the sources we used describe cave fish as a food fish, and there are good reasons not to catch them. Most are only 2 to 13 cm long, many exist in tiny numbers, and several are legally protected: the Alabama cavefish is federally endangered (Outdoor Alabama), and the northern cavefish is rated Near Threatened by the IUCN and Threatened by the American Fisheries Society, with over-collection listed among its threats (National Speleological Society). Leave cave fish where you find them, and follow cave-access rules.

The Alabama cavefish, Speoplatyrhinus poulsoni, is known only from Key Cave in Lauderdale County, Alabama. Outdoor Alabama describes it as 1.2 to 2.3 inches long, eyeless and unpigmented, and lists its threats as changes in groundwater quality and level and less organic input from bat guano, which feeds the cave's food web. It is federally endangered, and Wikipedia estimates fewer than 100 individuals. Another cave fish with a tiny population, the golden cave catfish, is put at fewer than 400 (Wikipedia).

Living without daylight changes more than the eyes. Wikipedia reports that the cave form of the Mexican tetra has a body clock of about 30 hours and Garra andruzzii of about 47 hours, instead of the usual 24. Many cave fish have low metabolic rates that let them survive long periods without food, and the Mexican cave tetra sleeps as little as 1 to 2 hours a day compared with 6 to 10 hours for its river relatives (eLife, 2025).

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