Heterandria formosa Girard, 1859

Taxonomic Introduction

Heterandria formosa Girard, 1859 is one of the smallest fish and smallest vertebrates documented by science.

Size

Males reach a maximum length of around 2 centimeters (0.8 inches), and females grow slightly larger, reaching around 3 centimeters (1.2 inches).

Body Coloration

This fish is typically olive in overall body color, with a dark horizontal stripe running through the center of its body.

Fin Markings

It also has a dark spot on the dorsal fin, and females have an additional dark spot on their anal fin.

Male Reproductive Morphology

Like most poeciliids, the anal fin of males is modified into a gonopodium, an intromittent organ used to deliver sperm and impregnate females during mating.

Genus Distribution in United States

Heterandria formosa is the only member of its genus Heterandria that occurs in the United States.

Native Range

Its native geographic range covers the southeastern United States, extending from North Carolina south through Georgia and Florida, and west across the Florida Gulf Coast to Louisiana.

Introduced Range in Texas

In recent years, this species has also been collected in eastern Texas.

Sabine River Basin Records

According to the North American Native Fishes (NANFA), it is recorded in the western part of the Sabine River basin.

Hurricane Harvey Dispersal Records

It has also been collected as far west as Humble, TX, in small sand pit ponds after the 2017 floods brought by Hurricane Harvey.

Aquarium Status

It is one of the few aquarium fish species that is endemic to North America.

Habitat

Heterandria formosa primarily lives in vegetated, slow-moving or standing freshwater habitats, though this species can also be found in brackish waters.