Three-lined aphyosemion (three-lined killifish)

Where they come from

Aphyosemion trilineatus is a West African killifish from small forest streams and swampy edges where the water is usually soft, a bit acidic, and full of leaf litter. Think shaded water, tannins, and lots of cover. That whole vibe translates really well to the aquarium, and they look even better over a dark substrate.

Setting up their tank

These fish are not hard, but they do punish sloppy setups. Give them a calm, covered tank with plants and you will have a totally different experience than in a bright, bare box.

• Tank size: 10 gallons works for a trio (1 male, 2 females). 15-20 gallons is nicer if you want a small group.
• Lid: non-negotiable. They jump, especially at lights-on, feeding time, or if they get spooked.
• Filtration: gentle. A sponge filter or a small filter with a prefilter sponge is perfect. They hate being blasted around.
• Decor: lots of plants (real or fake), floating cover, and hiding spots. Leaf litter (catappa/oak) makes them feel at home and helps calm them down.
• Substrate: dark sand or fine gravel makes their colors pop and keeps them less skittish.
• Water: I keep mine in soft to moderately soft water. Slightly acidic to neutral is a safe target. If your tap is hard, cutting with RO or rainwater can make life easier, especially for breeding.

Temperature wise, they do well in the low to mid 70s F. I have had the best luck keeping them a bit on the cool side rather than pushing tropical-warm. Stable matters more than chasing a number, so avoid putting them in a spot that swings hot/cold every day.

What to feed them

They are classic micropredators. Mine would pick at some prepared foods, but they really light up for live and frozen. If you want good color and steady spawning, this is the species that rewards you for feeding "real" foods.

• Staples: frozen bloodworms, brine shrimp, daphnia, cyclops
• Live foods that get the best response: baby brine shrimp, grindal worms, white worms (sparingly), live daphnia
• Prepared foods: small pellets or good flakes can work, but do not be surprised if they ignore them at first

Feed small portions once or twice a day. They will absolutely overeat rich foods like worms, and you will see it in bloating and messy water. A fasting day now and then is fine.

How they behave and who they get along with

Males are showy and will posture and chase, especially in smaller tanks. It usually looks worse than it is, but cramped quarters can turn it into nonstop stress. One male with two or more females is the easiest setup.

• Best kept as: a trio or small harem group with lots of cover
• Temperament: not a community angel, but not a terror either
• Good tankmates: small, calm fish that like similar water (think small tetras/rasboras, pencilfish), and peaceful bottom dwellers
• Tankmates to avoid: fin nippers, boisterous fish, and anything big enough to see them as snacks
• Shrimp: adults sometimes survive in a planted tank, but shrimplets are usually free food

Breeding tips

If you have ever bred other Aphyosemion, this will feel familiar. They are substrate spawners and will happily lay eggs in a spawning mop, fine-leaved plants, or leaf litter. You do not need anything fancy, just a routine.

• Breeding setup: 5-10 gallons, sponge filter, lots of cover, and one or two spawning mops (one near the surface, one lower)
• Pairing: one male and one or two females. Pull the male if he gets pushy.
• Water: softer and slightly acidic helps egg fertility and fungus resistance
• Egg collection: check mops every day or two and remove eggs to a small container with clean water
• Incubation: eggs typically take a couple weeks depending on temperature
• First foods: newly hatched brine shrimp is the easy button. Microworms work early too, but BBS grows them faster

If you leave eggs in the main tank, you might get the occasional surprise fry in a jungle of plants, but adults will hunt them. For a decent yield, pull eggs or move the adults out after a week of spawning.

Common problems to watch for

Most issues I have seen with three-lined aphyosemions come from stress: too much current, no cover, bad tankmates, or big swings in water quality. Fix the environment and a lot of "mystery" problems disappear.

• Jumping: the big one. Tight lid and block gaps.
• Hiding and washed-out color: usually too bright, too bare, or tankmates stressing them out.
• Fin damage: commonly from male sparring in small tanks or fin nippers in community setups.
• Skinny fish that will not eat: often newly imported or stressed. Try live foods, dim the lights, and give them cover.
• Fungus on eggs: common if water is hard/dirty or eggs sit in poor circulation. Keep egg container clean and remove bad eggs.