Orestias ctenolepis

Where they come from

Orestias ctenolepis is an Andean pupfish from the high-altitude lakes and streams of the Altiplano around the Titicaca basin. Think clear, cold, wind-churned water with a lot of dissolved minerals and a bright, high-elevation sun. They spend their days picking at tiny crustaceans and algae on rocks and aquatic plants.

Setting up their tank

Give them space to cruise and graze. A long tank is better than a tall one, with clean flow and plenty of oxygen.

• Tank: 24-30 in long footprint. A 20-long works for a group; 30-40 gallons is nicer.
• Group: 8-12+ to spread out any chasing.
• Temperature: 50-64 F (10-18 C). Short spikes to 68-70 F (20-21 C) are OK, not sustained.
• pH: 7.6-9.0. Hardness: GH 8-20 dGH, KH 6-12 dKH.
• Filtration: strong aeration and surface movement. Sponge + hang-on-back or canister with spraybar.
• Substrate/scape: fine sand with rounded stones, cobble, and patches of hardy, cool-tolerant plants (elodea, hornwort). Leave open lanes for swimming.
• Lighting: moderate to bright to grow periphyton (their snack bar).
• Lid: tight-fitting. They jump, especially at dusk and during courtship.

I run an air stone or open spraybar all the time. A small fan or chiller keeps temps in the sweet spot through summer. If your tap is soft or acidic, you will need to add buffering.

What to feed them

They are micropredators that also graze. Live and frozen foods get the best response, but mine learned some dry foods after a few weeks.

• Live: daphnia, baby brine shrimp, cyclops, mosquito larvae, small blackworms.
• Frozen: daphnia, cyclops, mysis, finely chopped bloodworm.
• Dry (once trained): small high-protein pellets or quality flake mixed with spirulina.
• Supplemental grazing: let some algae and biofilm grow on rocks.

Feed small portions 2-3 times a day. They are nibblers, not binge eaters. Skip one day a week if they are getting hefty.

How they behave and who they get along with

Active, curious, and busy. In a group they form loose shoals, pick at surfaces, and do short dashes. Males display with little flares and chases, but real damage is rare if the group is big and the tank has sight breaks.

I strongly prefer a species-only setup. Matching their cool temps and high pH narrows options, and they are quick at feeding time. If you must mix, try a small group of robust, cool-tolerant fish like white cloud mountain minnows and watch for food competition. No flowy fins, no tiny shrimp. Snails are fine.

Breeding tips

They scatter adhesive eggs in fine plants and algae. No parental care. You can get spawns in a community setup, but you will raise more fry if you collect eggs or dedicate a breeding tank.

• Sex ratio: 1 male to 2-3 females works well.
• Triggers: heavy feeding with live foods, a series of small cooler water changes, and a slightly longer photoperiod.
• Spawning media: yarn mops near the surface and a clump of fine plants or moss on the bottom.
• Collect mops every few days and hatch eggs in a shallow container with tank water and a gentle airstone.
• Incubation: roughly 10-18 days at 57-62 F (14-17 C).

Fry are tiny. Start with infusoria or rotifers for a couple of days, then move to newly hatched brine shrimp and microworms. Keep the rearing water mineral-rich and very clean with small daily changes.

Common problems to watch for

• Overheating and low oxygen in summer. Have a fan, chiller, or frozen water bottles ready.
• pH or KH crashes in soft water. Buffer and test regularly.
• Refusal to eat dry foods. Offer live/frozen first and train slowly.
• Wild-caught parasites. Quarantine new fish for 4-6 weeks and observe.
• Fin nipping of slow, long-finned tankmates.
• Jumping during stress or courtship.