Redtail Splitfin Identification Guide

Key identification features

• Deep, laterally compressed body with iridescent blue-gray coloration in males
• Bright orange-red band across the base of the caudal fin, without a dark border
• Split (bifurcated) leading ray of the anal fin in males, a defining goodeid trait
• Females are plainer, showing duller gray tones and a less vivid caudal band
• Compact size, reaching around 6 cm

Common look-alikes

• Butterfly splitfin: also has a caudal band, but it is yellow-to-orange and edged in black, unlike the unbordered orange-red band of the redtail splitfin.
• Other Xenotoca species: similar body shape but generally lack the same intensity or placement of the red tail band.
• Rainbow shiner: superficially colorful but is an unrelated egg-laying minnow without a split anal fin.

Where you'll see one

Redtail splitfins are native to springs and slow-moving streams of the Ameca River drainage in Jalisco, Mexico, typically found in shallow, warm, well-vegetated water. They often gather in small, active groups near the surface, where the males' flashing blue bodies and vivid tail bands are most visible in bright sunlight.