butterfly splitfin

The overall body coloration is silvery to golden, often enhanced with bluish or greenish hues on the sides. The pectoral, pelvic, and anal fins may have bright orange or reddish tones, particularly in males during courtship. Like all Goodeids, it has a "splitfin" (modified anal fin in males, but less specialized than the Poeciliid's gonopodium) and gives birth to fully formed fry. Its most distinctive feature lies in its high and wide dorsal fin, adorned with a pronounced black spot edged in white or yellow, resembling butterfly wings when spread.

Ameca splendens forms dominant groups often dominating the native community in its restricted habitat. It is mainly active in the spring area, where population density is highest, although it may also frequent downstream sections of the river.

It constantly grazes on algae and aufwuchs (biofilm composed of algae, bacteria, and detritus) adhering to rocks and concrete walls in the springs. This dependence on biofilms makes it particularly vulnerable to eutrophication.

Reproduction is matrotrophic viviparous, an advanced trait among teleost fish. Females give birth to free-swimming and independent fry. Although precise data on fecundity and seasonality in the wild are limited, the species successfully reproduces in captivity (notably in Florida, where it is commercially bred for the aquarium trade). Early sexual maturity (from 2.7 cm) allows for rapid generation turnover, a crucial strategy in the face of declining wild populations.