A Fish with Four Eyes – Anableps

A Fish with Four-Eyes - Anableps

God has equipped living things with some amazing equipment to enable them to survive in all kinds of environments. One example is the fish in the Anableps genus, which have what appears to be four eyes. These “fish with four eyes” live in the coastal waters of Venezuela and Trinidad and along the coastline to the northeast coastal areas of South America.

The Anableps eyes are located above the top of the head, and the fish swim on the water’s surface. They have two eyes out of the water to see what is above the surface and two eyes below the water to see what is there. Actually, they have only two eyeballs, each divided horizontally by a thin band of epithelial tissue. Each eye has two corneas and two pupils. The lens is oval-shaped, while the retina splits into two sections. The lens varies in thickness because of the difference in refraction between the air (index of refraction 1) and the water (1.33). That means light is bent differently for the bottom of the lens than for the top. To correct for that, the lens thickness varies, with the top being thicker than the bottom.

What is the advantage of being able to see above and below the water at the same time? The upper eye can detect insects, while the lower eye detects small fish, diatoms, algae, and small water creatures. That gives these fish with four eyes more food options.

What may not be obvious is how complicated the Anablep’s brain has to be to handle four sets of data. For example, when an upper eye sees a bug on the water’s surface and the lower eye sees a small fish, the brain has to know which part of the eye is sending the signal. Then it has to decide which food to catch and how to do it. Scientists are studying how the Anableps brain performs these tasks.

Anableps also have a very unique reproductive system, but we’ll save that for a later discussion. There is no way to trace an evolutionary process from a typical fish or a single cell organism to a modern Anableps. These fish with four eyes are another example of God’s design that allows life to exist in every environment and situation on Earth.

— John N. Clayton © 2021

Reference: Scientific American, August 2021, page 22

Four-Eyed Fish – Anableps

Four-Eyed Fish - Anableps

Throughout the natural world, we see special design features that allow animals to survive in environments that place unique demands. Chameleons have an eye-brain connection that enables the eyes to rotate independently of one another or work together when needed. Chameleons use their tongues to catch insects, but to capture their food, both eyes must work together to overcome depth perception issues. At the same time, chameleons are very vulnerable to predators, so their eyes must rotate independently to look in several directions at once. We find another example of unusual eyes in the genus of four-eyed fish, Anableps.

Anableps live in northern South America and Trinidad, where they swim in the surface waters of lakes and rivers. Near the surface, they are easy prey for birds, so they need to see above and below the water simultaneously. They appear to have four eyes, two above the water surface, and two below the surface. In reality, they are not separate eyes. The eyes are divided into two sections, separated by a band of tissue.

Each section of the Anableps eyes has two corneas, two pupils, a single egg-shaped lens, and one retina that is also divided. The portion of the eyes located above the water connects to a different section of the fish’s brain than the area below the waterline. These four-eyed fish are ideally suited to fill an ecological niche that no other fish can.

You might think that all fish could use this design, but every ecological niche has animals designed to inhabit and maintain that location. Anableps are unique, and that makes them popular aquarium fish. More importantly, this unique design speaks of God’s imaginative creativity in providing full use of every resource on planet Earth with creatures like the four-eyed fish, Anableps.

— John N. Clayton © 2020