Pataxo killifish

Where they come from

Pataxo killifish are annuals from eastern Brazil, mainly Bahia. They live in seasonal forest pools that fill with rain, stain dark with leaf tannins, then dry out. Adults die off in the dry season and the eggs wait buried in the mud until the rains return.

Setting up their tank

They do best in a species-only setup. A 15-20 gallon long tank works well for one male and two or three females. Keep a tight lid; they jump hard and fast.

• Water: very soft and acidic. Aim for pH 5.2-6.5, GH 1-3, KH 0-1, TDS 40-120 ppm. I use mostly RO water and tint with botanicals or peat.
• Temperature: 20-24 C (68-75 F). Short bumps to 25-26 C are fine, but avoid running them hot.
• Filtration: air-driven sponge filter with gentle flow. These fish dislike turbulence.
• Aquascape: dark sand or bare bottom with a layer of leaf litter (catappa, oak, magnolia). Add clumps of Java moss, fine plants, or yarn mops for cover.
• Spawning medium: a peat or coco fiber box/bowl 2-3 cm deep so they can dive to lay eggs.

What to feed them

They are micropredators and strongly prefer live food. You can get some onto frozen, but plan for live foods to keep them in condition.

• Staples: baby brine shrimp, daphnia, mosquito larvae (seasonal), grindal worms.
• Extras: blackworms (well-rinsed), white worms (sparingly), frozen cyclops or bloodworms for variety.
• Avoid: lots of dry foods. A few high-quality micro-pellets might be taken, but do not rely on them.

How they behave and who they get along with

Males display constantly and will scrap with other males in tight quarters. Keep one male per tank unless you are very experienced and have a lot of space and cover.

• Best kept as 1 male with 2-3 females.
• Shy at first but settle with cover and soft light.
• Not community fish. They prefer very soft, acidic water and will pick off small shrimp or fry.
• They jump. Leave no gaps in the lid, including around airlines and heater cords.

Breeding tips

They are classic annual substrate spawners. Give them a shallow dish of rinsed peat or coco fiber. They will dive and deposit eggs deep in the medium.

• Collecting eggs: lift the peat weekly, squeeze to just-damp (like a wrung-out brownie), and bag it with air in a labeled zip bag.
• Incubation: store at 22-24 C in the dark. Expect 8-16 weeks, but timing varies by line and temperature.
• Checking eggs: peek monthly. Eyes-up embryos look like tiny silver dots. If you see many eyed-up eggs, start test-wetting a small portion.
• Wetting: flood with very soft, slightly acidic water at 20-22 C. I use shallow trays so fry reach the surface easily.
• Fry care: first 24-48 hours they absorb yolk; then feed infusoria or vinegar eels, moving to baby brine quickly. Keep water shallow (5-8 cm) the first week to prevent belly-sliders.
• Staggered hatching: some eggs wake later. Re-dry the peat for 1-2 weeks and wet again to catch late hatchers.

Common problems to watch for

• Velvet (gold dust look, clamped fins) shows up fast in soft, warm water. Act early with darkness, increased aeration, and an appropriate med at killi-safe dosing.
• pH crashes in low KH systems. Test KH and pH regularly, and avoid overfeeding.
• Egg issues: fungus from too-wet peat, or poor development if stored too dry or too cold. Aim for just-damp and steady room temps.
• Male harassment: if a female hides constantly or shows torn fins, add more cover or split the group.
• Obesity from heavy worm diets. Mix in bbs/daphnia and add fasting days.
• Jumping during water changes. Drop the water level slowly and keep the lid on whenever possible.