Guaruba moenkhausia (Guaruba tetra)

Where they come from

Guaruba tetras (Moenkhausia guaruba) are South American characins from the Amazon basin region. Think warm, tannin-stained waterways, lots of leaf litter, roots, and shifting light under overhanging plants. They are not a "tiny creek" fish so much as a fish that likes cover, calm-ish flow, and room to cruise.

Setting up their tank

These are active, midwater tetras that really settle in when they have a group and some swimming length. I would not keep them in a cramped setup. A 20 long can work for a small group, but they look and behave better in a 30-40 gallon footprint where they can actually school.

• Tank size: 20 long minimum, 30+ gallons is where they start looking "right"
• Group size: 8-12 is the sweet spot (6 is the bare minimum)
• Temp: mid-70s to around 80 F (24-27 C) is a good everyday range
• pH/hardness: they adapt, but slightly acidic to neutral with moderate softness is easiest for color and breeding attempts
• Flow: gentle to moderate, with calm areas to rest

Decor-wise, you cannot go wrong with plants (real or good fake), a few pieces of wood, and some leaf litter if you like that look. I have had the best results with a darker substrate and background. Bright white sand under a strong light makes them skittish and they spend more time hugging cover.

Filtration matters more than fancy water chemistry. They do not love sudden swings, so keep up with steady weekly water changes and avoid letting nitrate creep. A tight-fitting lid is smart too - they can jump when spooked.

What to feed them

Guaruba tetras eat like most Moenkhausia: they are enthusiastic omnivores with a strong preference for small meaty foods. If you want good color and robust fish, mix a quality staple with frozen/live foods a few times a week.

• Staples: small pellets or crisp flakes they can finish quickly
• Frozen: daphnia, cyclops, brine shrimp, chopped bloodworms (not as the only food)
• Live (if you do it): baby brine, grindal worms, mosquito larvae where legal/safe
• Occasional extras: crushed spirulina flake or a veg-leaning micro pellet

How they behave and who they get along with

In a good-sized group, they are busy but not nasty. In a too-small group, you can see fin-nipping and a lot more chasing. That is usually the tank telling you "add more of us" or "we need more space and cover."

They are generally solid community fish with other similar-sized, non-bitey species. Think other medium tetras, pencilfish, hatchetfish, peaceful barbs, and calm dwarf cichlids. Corydoras and smaller plecos are usually fine too.

• Good tankmates: other schooling fish, Corydoras, Otocinclus, bristlenose pleco, peaceful gouramis, Apistogramma (with enough space)
• Use caution: long-finned fish (guppies, fancy bettas), very timid fish that hate commotion
• Not a match: aggressive cichlids, fin-nippers that will start a feedback loop, anything small enough to be seen as food (tiny shrimp can disappear)

Breeding tips

They are egg scatterers like many tetras, and adults will snack on eggs and fry if given the chance. Breeding is doable, but it is not a "set it and forget it" fish. If you want to try, a separate breeding tank saves a lot of frustration.

• Breeding tank: 10-20 gallons, dim light, mature sponge filter
• Spawning surface: moss, spawning mops, or a mesh/egg grate so eggs fall out of reach
• Conditioning: feed heavier for a week with frozen/live foods
• Trigger: slightly cooler water change, then back to warmer, plus lots of clean water
• After spawning: pull the adults or move the eggs, keep it dark for the first day

Fry are tiny, so plan food ahead. Infusoria and powdered fry foods get you started, then baby brine shrimp once they are big enough. Clean water is the whole game with tetra fry, but keep the flow gentle so they do not get pinned.

Common problems to watch for

Most issues I see with these come from stress: too few fish, too much light, not enough cover, or water that is not getting changed often enough. Stress shows up as pale color, clamped fins, hiding, and sudden spookiness.

• Fin nipping: almost always linked to small group size or cramped quarters
• Ich after a move: watch for flashing and white dots, usually after temperature swings or new fish
• Bloat/constipation: from overfeeding rich foods, fix with smaller meals and more variety
• Wasting/thin fish: internal parasites are possible in new imports, quarantine and treat if needed
• Jumping: startle response, especially in bright tanks with no floating cover

If you keep them in a decent school, give them a planted setup with open swimming space, and stay on top of water changes, they are really rewarding fish. They have that classic tetra energy without being nonstop troublemakers, as long as you meet them halfway.