# Least Killifish profile



## ChilDawg (Apr 30, 2006)

Least Killfish (_Heterandria formosa_)

(Got any pictures? I'd be happy to use them here...)

Name: Least Killifish
Other Names: Dwarf Livebearer, Dwarf Mosquitofish
Scientific Name: Heterandria formosa
Family: Poeciliidae

Distribution: Cape Fear River drainage in North Carolina to southern Louisiana
Length: 1.5"
Water Temperature: 68 to 79 degrees Fahrenheit (20-26 degrees Celsius)
Diet: Small live foods and some plant matter are preferred, but the least killie may take to small prepared foods.
Water Chemistry: Moderately hard to hard water is apropos for the care of this species.
pH: 7-8.3
Lifespan: 1-3 years

*Species Description* These are tiny guppy-shaped fish with mostly drab coloration. They do have some flash, as the rounded dorsals have black tips and a large black blotch in the region closest to the peduncle. A small red stripe extends across the border of said spot.

These also have a black lateral stripe which starts at the gill peduncle in males (it starts in the rostral region of females) and extends almost to a black dot on the caudal peduncle. Just anterior of the dorsal fin, this line is intersected by transverse bars which give the general appearance of a zipper across the posterior lateral surfaces of the least killie.

*Species Behaviour* These are crafty little active fish that just don't seem to want to be caught by net. They are great dithers for other small fishes and show no aggression toward anyone in their tank.

Though the females have somewhat of a reputation for consuming their progeny, well-fed females will not take part in this activity.

*Natural Conditions* Heavily-planted water that is stagnant to slow in flow.

*Natural Range* Cape Fear River drainage in North Carolina to southern Louisiana

*Minimum recommended tank size* 5 gallons

*Water Temperature* 68 to 79 degrees Fahrenheit (20-26 degrees Celsius)

*Water Quality* They like neutral to somewhat alkaline (pH 7-8.3) and moderately hard to hard conditions.

*Sexing* Females are markedly bigger than their male counterparts, may have more girth and have more dark black spots than just the one at the caudal peduncle of the male. The male has the typical poeciliid gonopodium, while the female has a large black splotch on her unmodified anal fin.

*Breeding* These fish breed best when kept in a colony filled with plants (on which the adults might munch and in which the young may hide).

Females may continuously produce one or two babies on a daily basis for upwards of two weeks. Don't expect any simultaneously "dropped" litters of Least Killie fry.

The young can take baby brine shrimp and other similarly sized foods at the time of birth.

*Feeding* Small live foods and some plant matter are preferred, but _H. formosa_ may take to small prepared foods.

*Miscellaneous Info* The world's smallest livebearing animal has the world's smallest possible list of synonyms: none. http://aquatic-hobbyist.com/phpBB2/viewtopic.php?t=9260 FishBase helped me with writing this, as did the "Peterson Guide to Freshwater Fishes."


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