To celebrate somebody finishing her Master’s research on a little, local, live-bearing fish this week, we present to you a fascinating not-so-little, not-so-local, live-bearing fish, Anableps anableps, the Largescale Foureyes.
First to get you in a relaxed state of mind, here’s maybe the best Euro fish video ever made, featuring the four-eyed fish: Allwetterzoo!
Found mostly along the coastline of northern South America and Trinidad in brackish lagoons and mangroves, the foot-long, frog-faced foureyes gets its names from a unique adaptation to life at the surface of the water.1 Swimming along the water’s surface, foureyes can watch for predator and prey above and below the surface of the water at the same time using specialized eyes that are really two eyes each (two retinas, two irises, all that).2 Each eye has an above-water eye adapted to terrestrial light and a below-water eye adapted to the yellow light of the murky mangrove water.3
Powerfact! These guys are part of a group of live-bearing one-sided maters who can only mate from one side! In live-bearing fish the male anal fin is modified to function as a penis. In one-sided maters, a male can only move its penis either to the left or to the right. So if he’s a lefty he has to approach a lady fish from the right and make sure he’s going for a complementary-sided female since the female genitalia is also one-sided.2 Tricky!
- Fish base.org: Anableps anableps
- Fish and tips!: Anableps anableps
- Owens et al. 2012. In the four-eyed fish (Anableps anableps), the regions of the retina exposed to aquatic and aerial light do not express the same set of opsin genes. Biology letters, 8(1), 86-89.