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Greater Seattle Aquarium Society

Het formosa: An Itty Bitty Livebearer

by Dave Sanford

Although it is referred to as the least killifish by some authors, Heterandria formosa is actually one of the smallest livebearing fishes. The females reach a maximum size of slightly over one inch, with the tiny males only measuring 1/2 to 2/3 of an inch. This diminutive size is their major charm and makes them ideal residents in a small aquarium, down to 2 gallon size.

[Male]

These fish have slim bodies with a dark lateral stripe, a black blotch at the base of the dorsal and anal fins. The dorsal fin of both sexes also has a hint of dark red.

Considering their very mild temperament they do best in a species tank without competition from other fish. In addition to making an interesting display, a variety of live plants including Java moss will provide microscopic life to supplement their feedings of small live foods like baby brine shrimp and cyclops. Crushed flakes will also be eaten. I find that a sponge filter will give them a source of snacks as well. I think the addition of a few ghost shrimp or bee shrimp would liven up the tank and pose no harm to the Hets. Allowing some algae to grow on the nonviewing sides of the tank will encourage them to graze there as well.

[Female]

Water in the range of pH 6.5-7.5, and soft to moderate hardness is ok. Frequent partial water changes, especially in small tanks, is a must to maintain good water quality.

After about one month, the pregnant females will deliver one or a few tiny fry over a several day period. They need to have microscopic food at first so don’t keep the tank too clean! Parents don’t seem to take an interest in eating the fry so I just leave them with the parents. They grow fast and begin courting at an amazingly small size.

Although not a flashy fish that will have commercial appeal, these tiny fish are special and deserve to be considered by anyone with even a passing interest in livebearing fish.