The rainbow goodeid (Characodon lateralis) is a species of critically endangered freshwater fish in the family Goodeidae,[2] and are endemic to Mexico.

The rainbow goodeid is a small sexually dimorphic fish, averaging 42mm in size for males and 65mm for females.

[3] Males are generally more colorful and larger-bodied, showing a blue or green body with red accents and a silver luster.

The genus Characodon as a whole is estimated to have diverged 15.5 mya, making it the oldest branch of the family Goodeidae.

[3] The rainbow goodeid is typically found in freshwater, shallow springs or marshes with little to no current and plentiful submerged vegetation.

[5] Clear to turbid water is ideal for this species, with a substrate consisting of sand, mud, silt, clay, rocks, or a marl bed.

They have been found in the Abraham Gonzalez spring,[6] around the El Salto waterfall on the Rio Tunal River,[2] Los Berros,[1] distributaries of the upper Rio Mezquital River,[3] springs connected to Laguna El Toboso, and a private property in La Constancia.

Many of the springs that they inhabit have dried up or been overcrowded with invasive species, so the number of suitable locations has been decreasing.

They face multiple major threats including the introduction of invasive species, pollution, agricultural runoff, urban sewage, disturbance from recreational activities, dams/ water management, disease, and climate change.

In surveys, researchers have found predatory species that either kill the fish or increase competition for resources.

Crayfish (Procambarus clarkii), Tilapia (Oreochromis neloticus), and Green Swordtails (Xiphophorus hellerii) are major competitors.