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 These fish swim along the water’s surface keeping an eye out for prey and predators above and below the water using eyes composed of an above-water eye and a below-water eye, each with its own retina and iris, separated from each other by an opaque band of tissue.2 Each eye is adapted to different light environments with the above-water eye more sensitive to the green terrestrial light and the below-water eye more sensitive 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 functions as an intromittent organ. A male can only move it to the left or to the right. So he’s gotta not only approach a lady fish from the correct side but also go for a complementary-sided female since the female genitalia is also one-sided and can only be accessed from either the left or the right.2 Sounds tricky!