Butterfly Splitfin Identification Guide
Recognize the Butterfly Splitfin by its deep body, black-edged caudal band, and split male anal fin.
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Key identification features
- Deep, laterally compressed body in greenish-gray to olive tones
- Bold yellow-to-orange band at the base of the caudal fin, bordered by a black edge
- Males show enlarged dorsal and anal fins with dark margins
- The male anal fin has a distinctive split (bifurcated) leading edge, a hallmark of goodeid livebearers
- Compact size, roughly 6-8 cm, with males smaller and slimmer than females
Common look-alikes
- Redtail splitfin (Xenotoca eiseni): also has a caudal band, but it is orange-red without the bold black border and the body is more elongated.
- Other goodeids such as Ilyodon species: lack the sharply defined black-and-yellow caudal band entirely.
- Livebearing mollies: share a similar deep-body silhouette but lack the split anal-fin ray structure unique to goodeids.
Where you'll see one
Butterfly splitfins originate from warm, spring-fed rivers of the Ameca River basin in Jalisco, Mexico. The species is extinct in its original wild habitat but persists through captive populations and targeted reintroduction efforts in restored spring systems.
Frequently asked questions
How do I recognize a butterfly splitfin at a glance?
Check for a deep-bodied fish with a black-bordered yellow-orange band at the tail base and, in males, notably enlarged dorsal and anal fins.
How do I tell a butterfly splitfin from a redtail splitfin?
Look at the caudal band: the butterfly splitfin's band has a black outline, while the redtail splitfin's orange-red band lacks that dark border.