My Experience Breeding Least Killifish (Heterandria Formosa)

The Least Killifish (Heterandria Formosa), is an interesting livebearer native to the United States (specifically in Florida and surrounding areas). Although it has “Killifish” in the common name, it is actually not a killifish, and is in the Poeciliidae family. That family consists of fish such as Guppies, Platies, Swordtails, and Molleys. As of 1991, it was the smallest fish found in North America, and the 7th smallest in the world! The females grow to just under an inch and a half big, and the males grow to about 3/4s of an inch big! 

Being such a small fish, and the fact that they are native to Florida, actually makes this fish a very good choice for beginners and experienced fish keepers alike! They aren’t picky eaters, and will eat pretty much anything handed to them. I fed mine everything from flake food, powdered fry food, frozen food, and even left over live food such as microworms and baby brine shrimp. They also tolerate temperatures of 66-76 degrees fahrenheit, although mine did great at 78 degrees and talking to many members of the club, they do great in outdoor tubs year around as well with our warmer California climate. This means they would do fine in an indoor aquarium without a heater (in most cases). I kept mine in a PH of 7.4 (my tap waters PH). I started with 6 in a 10 gallon, and after a few months I had 30+! I did a weekly 80% water change, which is fairly heavy, but I do that same change on most of my breeding tanks since I feed those tanks heavy. 

One of the most interesting things about the Least Killifish (at least in my opinion) is how it reproduces. Like I said, it is a livebearing fish, but it reproduces through a process called Superfetation. Superfetation is the simultaneous occurrence of more than one stage of developing offspring in the same animal. What this means, is that although these fish reproduce quickly like guppies, they don’t give birth to one large group at once. A good way of explaining I saw online was they are more like a conveyor belt. Rather then dropping all of their fry at once, they give birth to a single (or a small group) of fry every other day. I never knew that that was even a thing, and it just fascinates me!

I kept mine in a bare bottom 10 gallon tank with a ball of Java Moss that was about the size of a football. This gave plenty of cover for the fry, while being an easy to clean tank. While these fish are very muted in color, I really enjoyed the black line and stripes on their brown body. They are a shy fish, but I believe they would look stunning in a heavily planted aquarium, where the plants are more of the focus point. I plan on doing a tank like that myself sometime soon. While they are muted in color, they were one of the favorites by guests once they found out they were native, and such a small fish! They may not be the prettiest fish, but they are definitely a cool fish!