Amphilophus citrinellus is a large cichlid fish endemic to the San Juan River and adjacent watersheds in Costa Rica and Nicaragua.

A multivariate approach to treatment of anatomical characters has facilitated the discrimination among very similarly shaped species, aided by behavioral and ecological evidence.

Multiple species of this group have been identified and verified by genomic and mitochondrial DNA evidence in volcanic crater lakes Apoyo[1][2] and Xiloá.

Colorations and morphological characters (e.g. accentuated nuchal humps) seen in the hobbyist trade are the product of selective breeding for several generations and may not be reflected in the wild.

The final member of the complex, Amphilophus astorquii, constitutes about eighty percent of the breeding population of Laguna de Apoyo.