New Fish Cells Rewrite Vision Science

For over a century, textbooks have described vertebrate vision as relying on two distinct cell types: rods for dim light and cones for bright light and color. However, new research has identified a novel visual cell in deep-sea fish that defies this established dichotomy.

Scientists discovered these hybrid cells in the larvae of three Red Sea fish species: Maurolicus mucronatus (hatchetfish), Vinciguerria mabahiss (lightfish), and Benthosema pterotum (lanternfish). These cells combine the rod-like shape, optimized for capturing light, with the cone's molecular machinery and genes.

While most of the studied fish shifted to typical rod-cone vision in adulthood, the hatchetfish retained these hybrid cells throughout its life. This evolutionary adaptation allows these small fish, measuring 1-3 inches as adults, to navigate the dim twilight zones of the ocean, typically found at depths between 65 to 650 feet.

The findings, published in Science Advances, suggest that vertebrate visual systems are more adaptable and flexible than previously understood. Researchers propose that these blended photoreceptor types might be more common across various vertebrates, including terrestrial species, challenging the strict separation of rods and cones.