Carvalho's tetra

Where they come from

Carvalho's tetra (Tetragonopterus carvalhoi) is a South American river fish. Think warm, tannin-stained water, leaf litter, branches, and that constant gentle current you get in rainforest tributaries. They are not a "tiny nano tetra" type of fish - they come from places where they have room to move and they use it.

Setting up their tank

Give them length more than height. A longer tank lets them school, chase a bit, and burn off energy without turning your aquarium into a wrestling match. I have had the best results in tanks that feel "open" across the front with plants and wood breaking up sight lines.

• Tank size: I would not bother with less than a 30 gallon, and 40 breeder style tanks are even better if you can swing it
• Group size: 8-12+ keeps their attention on each other instead of on tankmates
• Filtration: steady, clean water with moderate flow; they appreciate current but do not need a jet stream
• Temperature: mid-70s F is a sweet spot (roughly 74-78F)
• pH and hardness: they are pretty flexible if you keep it stable; slightly acidic to neutral is the easy lane

Decor-wise, I like a mix of: a couple pieces of driftwood, a patch of dense plants on each side, and open swimming space through the middle. Leaf litter (catappa/oak) is optional, but it makes them look more natural and seems to take the edge off their spicier moments.

What to feed them

They eat like little piranhas that read the rules first. Mine did great on a staple of quality flakes or small pellets, but they really come alive (and color up) with regular frozen foods.

• Staples: good flake, micro pellets, small sinking pellets if they will take them
• Frozen: bloodworms, brine shrimp, daphnia, mysis (rotate a few)
• Occasional: live foods if you have them (they go nuts for live daphnia)
• Plant matter: a bit of spirulina flake now and then helps, especially if they start sampling soft plants

How they behave and who they get along with

Carvalho's tetras are active, social, and a little rowdy. In a proper group they spend most of the day schooling and doing quick little dominance squabbles. In small numbers, that same energy turns into fin-nipping and bullying.

• Good tankmates: other medium, sturdy characins; peaceful barbs; bottom fish like Corydoras; larger plecos; many dwarf cichlids if the tank is big enough and has hiding spots
• Use caution with: long-finned fish (angelfish, fancy guppies, bettas) and very timid species
• Avoid: tiny nano fish they can harass, and anything slow with trailing fins

Breeding tips

They are egg scatterers, and adults are not shy about eating their own eggs. You can get spawns in a community tank, but you usually will not get survivors without a separate setup.

• Breeding tank: a small bare-bottom tank works, with a sponge filter and either a spawning mop or a thick mat of fine plants (Java moss is the classic)
• Conditioning: feed heavy on frozen/live foods for 1-2 weeks
• Trigger: a slightly cooler water change followed by warming back up often gets them going
• After spawning: pull the adults or move the eggs; keep lighting low

Fry are tiny at first. Start with infusoria or very fine powdered fry food, then move to baby brine shrimp as soon as they can take it. Clean water matters a lot at this stage, so do small, frequent water changes.

Common problems to watch for

Most issues I have seen with these guys come from crowding, too-small groups, or inconsistent water quality. They are hardy, but their behavior will tell you quickly when something is off.

• Fin nipping: usually not "a mean fish" problem, more a group size/tank layout problem
• Stress fading: pale colors and hiding often means lighting too bright, no cover, or unstable parameters
• Ich after big swings: they can pick it up after temperature changes or after adding new fish without quarantine
• Bloating/constipation: common if you lean too hard on dry food; add daphnia and cut back for a day