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Least Killifish
Heterandria formosa
Animalia›Chordata›Actinopterygii›Poeciliidae
📍 Southeastern USA, Florida to South Carolina
One of the smallest vertebrates in the world — females reach just 1.5 inches. A fascinating livebearer from the USA that thrives in cool, planted nano tanks. Ideal for a species setup.
Care Guide
Diet
Least Killifish are omnivores that thrive on a varied diet of small foods. Offer high-quality micro pellets, crushed flakes, and small frozen foods like brine shrimp and daphnia once daily in small portions. Supplement with occasional live foods such as copepods or small insects to promote natural foraging behavior.
Behavior
These tiny, peaceful fish are active swimmers that prefer to stay in mid-water zones among plants. They are schooling fish that feel most secure in groups of 3 or more and display minimal aggression toward tankmates. Males may exhibit mild territorial behavior, but overall they are docile and ideal for planted nano aquariums.
Breeding
Least Killifish breed readily in captivity and are prolific livebearers, with females producing small broods regularly. Provide dense vegetation (Java Moss, Riccia, or similar) where fry can hide immediately after birth, as adults will consume them. Expect fry to appear frequently in established tanks with good conditions; separate them to a nursery tank if you wish to raise them.
Tank Mates
Similar size, peaceful temperament, and compatible water parameters make them ideal companions
Small shrimp won't be harmed; they occupy different ecological niches and help with algae control
Peaceful algae eaters that thrive in the same cool, planted nano tank environment
Tiny bottom-dwellers that won't compete for food or space in small tanks
Peaceful scavengers that help maintain water quality without threatening fry
Common Diseases
Ich (White Spot Disease)
White spots on body and fins, rapid breathing, lethargy, rubbing against plants
Raise temperature gradually to 26-28°C, perform daily 25% water changes, and treat with aquarium salt or ich medication; ensure good filtration and water quality
Fin Rot
Frayed or deteriorating fins, discoloration at fin edges, lethargy
Improve water quality with frequent partial water changes, reduce stocking density, treat with antibacterial medication if severe
Velvet Disease
Fine golden or rust-colored dust on body, rapid breathing, loss of appetite, scratching behavior
Increase aeration, perform daily water changes, treat with copper-based medication or increase temperature to 28°C; quarantine affected fish
Dropsy
Bloated abdomen, scales standing out, lethargy, loss of appetite
Isolate affected fish, improve water quality, provide varied diet with quality foods; unfortunately often fatal if advanced
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Quick Facts
- pH
- 6.0–8.0
- diet
- omnivore
- maxSize
- 1.5 inches
- minTankSize
- 3 gallons
- temperature
- 59–79°F (15–26°C)
Temperature
59–79°F
15–26°C