When observing nature, it’s easy to see how different environments have played a role in certain adaptations which allow animals to thrive in the area that they’re in. For instance, giraffes developed long necks over millions of years because those with longer necks survived long enough to pass their genes on. The same can be said for animals who have evolved to get rid of certain attributes, or organs, that are cumbersome to their environment.
In this blog, we’ll explore which types of fish are blind, why they’re blind, as well as the environments that they live in.
Why are some fish blind?
The exact reason why fish become blind isn’t certain, but our best guess is that they simply did not need their eyes and so have started to lose their eyesight. Blind cave fish, for example, develop in their eggs with eyes but once they’ve been born, their eyes begin to degenerate due to a lack of light.
Most blind fish wouldn’t have much use for their eyes even if they did possess them because there is so little light that they wouldn’t be able to see much anyway! Blind fish save a lot of energy by not dedicating valuable resources to a sense which wouldn’t be of much use.
The loss of eyesight in some fish is described as an epigenetic one, meaning that there is a change to how the gene is expressed rather than a change to the genetic code itself. In theory, the gene could be expressed differently by another fish further on in the family tree.
What species of fish can’t see?
There are many species of fish that cannot see, and unsurprisingly, many of them live in caves where light is limited so they don’t have much need for eyesight. Let’s explore some of them!
Mexican tetra
The Mexican tetra (Astyanax mexicanus), commonly called the blind cave fish, is probably the most well-known blind fish. These small, translucent fish live in small groups called shoals. These fish are most comfortable in temperate water of between 18-21 °C in small caves, rivers, lakes or ponds throughout Central America. Despite their exotic nature, they’re a relatively easy fish to keep in the aquarium hobby.
Southern cavefish
The southern cavefish (Typhlichthys subterraneus)is a small, slender fish that inhabits low-light waters of the eastern United States. Southern cavefish have limited feeding options in their habitat, relying on small invertebrates such as copepods and crayfish.
Ozark cavefish
The Ozark cavefish (Amblyopsis rosae) is another small, slender, translucent fish. Similarly to their eyesight, pigmentation requires extra energy that would be a waste, which is why cave fish tend to be colourless. The Ozark cavefish is native to the United States, inhabiting the same caves as the southern cavefish in Arkansas, Missouri and Oklahoma.
Cave crayfish
It’s not just fish that have ditched their eyesight to match their conditions, other animals such as the cave crayfish also share the same characteristics, with no eyesight and a lack of pigmentation. Cave crayfish typically feed on isopods and a range of other animals to survive in the caves of Arkansas.
How do blind fish survive?
You might be wondering how difficult it must be to be without eyesight in such a dangerous environment surrounded by predators, but blind fish are remarkably adapted to make the most of their surroundings, even if they are still vulnerable.
Firstly, they have incredibly sensitive lateral line organs which detect water displacement so that they can navigate the space that they’re in. During the mating ritual of Mexican tetra, the two parties will make exaggerated movements so that they can find each other without seeing each other, which gives a whole new meaning to a blind date!
Secondly, they’re not fussy eaters, feasting on just about any prey they can fit in their mouths. This allows them to keep their energy levels high to evade predators and continue to mate even if food is seemingly scarce.
Learn more at Hastings Aquarium
There’s clearly more than meets the eye with these fish and in person, they’re even more spectacular in environments that mimic their natural habitat.
You can show off your newly-found knowledge to your family and friends down at Hastings Aquarium by booking your tickets and making a trip to our extraordinary exhibits.