I think this is the first I have seen anyone with Mexican tetras in their pond. Very neat! They are pretty aquarium fish and are often traded in the native fish aquarium trade.
They are more of stream/creek fish, interesting this one was collected from a pond. Does this pond have a feeder creek or experience occasional flooding from a nearby creek?
They reach about 4" in size, so they certainly can be a forage fish. One that doesn't get so large to not be effectively preyed on. However, like many forage species they are predacious in nature and feed on other living animals and such will compete with young bass and sunfish for food.
Food habits from the Texas Fish ID website: This species is usually highly carnivorous, feeding on smaller fish, although in northeastern Mexico it has been reported to be omnivorous, with plants, filamentous algae, and aquatic insect comprising the bulk of its diet (Birkhead 1980). In the lower Rio Grande, diet includes green algae and plants, various terrestrial and aquatic insects, and occasionally fish (majority Gambusia affinis; Estrada 1999); at Phantom Springs, near Toyavale, Texas, tetras consumed similar foods as did lower Rio Grande population, although no fishes were observed in the diets of individuals from Phantom Springs (Winemiller and Anderson 1997). In each of three Balmorhea State Park environments sampled, a variety of foods were consumed, including green algae, amphipods, ostrocods, insects, crayfish, snails, and (at one site only) fish (Edwards 1999). Young-of-year observed feeding voraciously on insects, in Waller Creek (tributary of Colorado River), Texas (Edwards 1977).
