darter characin

Where they come from

Darter characins (Melanocharacidium rex) are little South American stream fish. Think clear, shallow creeks with sandy runs, scattered pebbles, and a steady push of water. They hug the bottom, scoot between stones, and pick at tiny critters the current brings.

Setting up their tank

They care way more about floor space and flow than height. If you can give them a long footprint, clean sand or fine gravel, and good oxygenation, you are most of the way there.

• Tank size: 20-gallon long or larger for a small group (they use the bottom like a runway).
• Substrate: fine sand with scattered smooth pebbles and a few larger rounded rocks.
• Hardscape: build lanes and line-of-sight breaks with stones, wood, and leaf litter. They appreciate shady pockets.
• Plants: tough, attached types like Java fern, Anubias, or moss on rocks. Stems tend to get battered in the flow.
• Filtration and flow: a canister or HOB with a prefilter sponge, plus a small powerhead to create a brisk current along one side.
• Water: soft to moderately hard, pH around 6.0-7.2, coolish tropical temperatures (70-77 F / 21-25 C). Keep it well oxygenated.
• Lighting: moderate. They relax more with some dappled shade from wood, plants, or floaters.

What to feed them

They are little predators by nature, so start with moving foods. Once they get settled and confident, you can mix in prepared stuff.

• Go-to foods: live or frozen baby brine shrimp, daphnia, cyclops, mosquito larvae, grindal/blackworms (rinsed).
• Good additions: finely chopped mysis, small bloodworms (sparingly), quality micro-pellets that sink, crushed granules, or a smear of Repashy gel on a rock.
• Feeding style: small amounts 2-3x daily. Let the current carry food along the bottom so they can dart and grab like they do in the wild.

How they behave and who they get along with

Picture tiny freshwater sculpins with tetras' faces. They sit, stare, and then zip a few inches to the next spot. Males posture and chase a bit, but real damage is rare if they have cover.

• Group size: keep 6+ to spread squabbles. Visual breaks help a lot.
• Tankmates: peaceful, quick midwater fish that will not bulldoze the bottom. Pencilfish, smaller tetras that handle flow, or hatchetfish up top work well. Small, gentle loricariids can share the bottom if there is space.
• Avoid: big cichlids, boisterous barbs/danios that outcompete at feeding, and slow fancy fish that hate current. Shrimplets may get picked off.

Breeding tips

They are open scatterers with no parenting instincts. It is doable but a bit niche. I have had the best luck in a cool, high-oxygen setup with fine sand, pebbles, and a thick pile of leaf litter or yarn mops they can dive into.

• Condition a group with plenty of live foods.
• Trigger with a large, slightly cooler water change and a bump in flow.
• Spawning looks like quick chases and short presses over sand, under leaves, or between pebbles.
• Adults will snack on eggs, so either remove them after a spree or move the leaf pile/mop to a rearing tank.
• Eggs hatch in a couple of days depending on temperature. Start fry on infusoria/green water, then microworms and newly hatched brine shrimp once they can take it.
• Use a gentle sponge filter in the fry tank so nobody gets pinned to an intake.

Common problems to watch for

• Low oxygen: if they are breathing fast and hugging the highest-flow spot, add surface agitation and check temperature.
• Heat stress: they do poorly during summer spikes. A fan across the surface or a small chiller helps.
• Refusing dry foods: keep offering tiny portions mixed with frozen. Do not rely on flakes; they want sinking, bite-sized stuff.
• Parasites on new, wild-caught fish: quarantine and deworm if needed. They are sensitive, so go slow and keep water pristine.
• Substrate injuries: sharp gravel scrapes bellies and fins. Use fine sand and smooth pebbles.
• Clogged intakes: they sit right in the flow. A prefilter sponge prevents them from getting pinned and keeps micro-food in the system a little longer.