Nutrition
The Mexican tetra is a predatator. It is a meat meating fish that preys primarily on insects, smaller fish, snails and crustaceans. They will also feed on plant matter as well (Arkive 2013).
The surface fish is the top predator of Northern Swordtails, a species of fish that inhabit some of the same areas. The swordtails have a rather flashy "sword" on the ventral portion of their tale (Cummings et al. 2003). Check out interactions to see how the swordtail has tricked the tetra.