Mosquito Fish vs. Guppies & Endlers

I often see questions about how to tell Mosquitofish (Gambusia sp.) from Endlers or Guppies (Poecilia sp.), so I made this easy graphic.

At first glance, these fish can look very similar, especially in photos. Males are usually fairly easy to identify thanks to their bright colors, but females, especially Endlers, are where most of the confusion comes from. Female Endlers and guppies can look surprisingly similar to Gambusia, and color or spotting is not always reliable. Lighting, stress, and photo quality can all make those traits hard to judge.

Because of that, my go-to method for identification is checking dorsal fin positioning. In Gambusia, the dorsal fin sits much farther back on the body, which makes them surprisingly easy to identify once you know what to look for. Most other livebearers have a dorsal fin that lines up with or even starts before the anal fin. The only exception to that rule I can think of is H. formosa, the Least Killifish.

If you are trying to identify a fish and are unsure, focusing on body structure instead of color will usually give you a much more reliable answer.

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