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Blind Cave Fish (Astyanax mexicanus). You may have heard the expression ‘as blind as a bat’, but the Blind Cave fish, or Mexican tetra, take it one step further by not having any eyes at all!

Interestingly, not all of these tetras are missing their eyes. These fish can be divided into two subspecies, one of which lives in fast flowing rivers, streams and lakes near the surface, and one that is only found in caves. The first form is similar to most tetra species, with silvery scales and two big, dark eyes on either side of their head with normal vision. The second, cave dwelling form, have varying levels of vision, depending on where they are found. Some populations have limited sight, whilst other populations are completely blind, some even losing their eyes completely. These blind cave fish also have no skin colouring and clear fins.

The lack of vision or even having no eyes at all is actually a good thing if you are cave fish, however. Cave habitats are generally dark with very little food or oxygen available, so anything that saves energy will give the fish an advantage. Scientists have researched into the energy savings from not having eyes or parts of the brain dedicated to vision. They have found a significant energy saving from being blind compared to having vision, giving the blind forms an advantage in places where sight is not necessary.

Luckily the blind cave fish are not helpless without sight, as they have a sensitive lateral line organ that helps them navigate their environment. All fish have a lateral line, which is a series of tiny pores along the side of the fish which help them to detect changes in pressure and vibrations in the water. This organ is particularly strong in these cave fish, helping them navigate their environment and find food.



What do they eat?

Small insects, crustaceans and plants



Water Type

Freshwater lakes and streams in lakes

Where are we?

Caves of Mexico, Guatemala and the United States

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