How Deep-Sea Fish See In The Dark

Although some fish that live deep in the waters have evolved over time to not have eyes at all, there are still some that prefer having the power of sight. According to science, some of these deep-sea fish see the world through more than just different shades of gray.

A recent survey of 101 fish species revealed that four deep-sea creatures have a surprising number of genes for light-sensitive eye proteins. Called rod opsins, this discovery is startling and can potentially change a lot of what we know about fish that live in the deep, as well as how they employ those light catchers to potentially see color.

Before the recent survey, it was believed that there are few deep-sea species that have eyesight, and if they do, they mostly see in gray. This is because light is usually not strong enough to reach the deep parts of the sea, causing the fish in it to evolve and adapt accordingly.

The survey was part of a study made by Musilova and Fabio Cortesi of Brisbane, Australia’s University of Queensland, who decided to sail on research ships equipped with devices meant to reach the deeper parts of the ocean to gather data. According to the researchers, the species they surveyed all came from the “twilight zone,” which is some 200 to 1,000 meters from below the surface. In here, light barely passes through, and most of the light you will see are from bioluminescent species that use their glow to either attract prey or use it to find their mates.

The four types of fish with the special eyes came from three different lineages. Furthermore, all three lineages have independently evolved genes for more than one type of RH1 rod opsins, light-detecting cells. The four fish are the glacier lantern fish (with genes for five different forms of RH1), the tube-eye (six different forms of RH1), the longwing spinyfin (18 genes) and the silver spinyfin (38 genes).

Despite their discovery, the authors are still not claiming that these deep-sea fish can see color, only that there’s the possibility that they can see more than just plain shades of gray. However, even with all of the uncertainty, finding the unexpected rod opsins in the fish is still a significant discovery.