Penguin tetras are active, peaceful schooling fish with a bold black stripe and an unusual head-up swimming angle. They get along with calm fish of similar size, adapt to a wide range of water, and stay under about 2.5 inches long.
Their main weakness is fin nipping. Keep them in a group of at least six (ten or more is better), and avoid long-finned tank mates. They also have little tolerance for ammonia, nitrite, and high nitrate, so clean water is non-negotiable.
TABLE OF CONTENTS
Penguin Tetra Facts & Overview
| Category | Rating |
| Care Level: | Easy |
| Temperament: | Peaceful, but may nip long-finned tank mates |
| Color Form: | White and silver translucent with black stripe |
| Lifespan: | 3–6 years (around 5 is common) |
| Size: | 1.5–2.5 inches |
| Diet: | Omnivore |
| Family: | Characidae |
| Minimum Tank Size: | 20 gallons with a long footprint, for a school of 6–10 |
| Tank Set-Up: | Freshwater; heavily planted back and sides, open swimming space in the middle |
| Compatibility: | Calm schooling fish of similar size; avoid long-finned fish |
The penguin tetra (Thayeria boehlkei) is native to the upper Amazon basin in Peru and the Rio Araguaia in Brazil. It lives in backwaters, flooded areas, and tributaries. It is a micro-predator that feeds on small crustaceans, insects, and worms. In the wild it shelters among dense plants and tree roots, in dim, tinted water.
The fish you buy are bred in captivity, but they still do best with plants, shade, and some live or frozen protein.
Other common names include blackline penguin fish and hockey stick tetra. Thayeria boehlkei is often sold as the “penguin tetra,” a name first used for the similar Thayeria obliqua. The two look alike and are kept the same way.
Penguin tetras grow to about 1.5 to 2.5 inches (roughly 4–6 cm). Reported lifespans run from about 3 to 6 years, and keepers commonly see around 5.
Typical Behavior
Penguin tetras are best known for their swimming posture, with the head tilted slightly up, and for fin nipping. The nipping is usually minor or absent when you keep them in a proper group, because they spend more time interacting with each other than bothering other fish.
They are schooling fish. Alone or in a small group they get nervous and are more likely to nip. A group of 6 is the minimum, and 10 or more gives the best behavior.
They find flowing fins hard to ignore. Skip long-finned fish unless the tank is large enough for them to keep their distance.
Appearance
Penguin tetras have a thick black stripe that runs from behind the gill cover to the tail. Their bodies are silvery white to olive, with a translucent silver belly. Their swimming style, with the head tilted up, makes them easy to identify.
How can you tell males from females?
The differences are subtle. Adult females are a little rounder in the belly, especially when carrying eggs, and a bit less intensely colored. Males are usually slimmer and more brightly colored. Look from above to compare body width.
Habitat and Tank Conditions
Penguin tetras swim in the middle to upper part of the tank, so substrate matters less. Sand or small smooth gravel is fine. Plant the back and sides heavily, and leave open swimming room in the middle.
Plants, roots, and driftwood help them feel secure. Floating plants soften the light. You can tint the water with dried leaves or tannin-releasing wood, but only if you remove leaves before they rot, because decaying leaves raise ammonia and nitrite.
Water Conditions
Penguin tetras are adaptable. They tolerate a wide range of pH and hardness, but they need clean water and do not tolerate ammonia or nitrite.
Commonly reported parameters are:
- pH: about 5.5 to 8.0 (6.0 to 7.5 is a safe range)
- Hardness: up to about 20 dGH (3 to 15 dGH is typical)
- Temperature: 72°F to 82°F (22–28°C), with the mid-70s a good target
Test ammonia, nitrite, and nitrate weekly. Aim for zero ammonia and nitrite and nitrate below about 20 ppm. Do regular partial water changes.
What Size Aquarium Do They Need?
Plan on at least 20 gallons for a school of six to ten. Seriously Fish suggests about 18 US gallons for a small group, with a long footprint (around 24 inches) so the school has room to swim. A 30-gallon tank is better if you want a bigger school or other fish in the tank.
Tank Mates
Penguin tetras do best with calm, peaceful schooling fish of similar size. They get along with other tetras, rasboras, small barbs, corydoras, and dwarf gouramis. Avoid fish that are aggressive, much larger, or very boisterous.
Stay away from angelfish, guppies, Siamese fighting fish, and other long-finned fish. Penguin tetras may nip their fins.
Also avoid large fish that could eat them.
Good tank mates for penguin tetras include:
- Bloodfins
- Cherry barbs
- Corydoras
- Diamond tetras
- Dwarf gouramis
- Emperor tetras
- Flame tetras
- GloFish
- Harlequin rasboras
- Head-and-tail-light tetras
- Kuhli loaches
- Lemon tetras
- Mollies
- Oto catfish
- Pearl gouramis
- Platies
- Redeye tetras
- Silver hatchetfish
- Silvertip tetras
- Swordtails
- Zebra danios
Some fish often listed as tank mates need conditions. Black skirt tetras, serpae tetras, and rosy barbs are nippy or boisterous themselves, so only try them in a large tank with plenty of cover. Buenos Aires tetras, silver dollars, Congo tetras, clown loaches, iridescent sharks, and red tail sharks grow much larger, so they need a big tank. Blind cave tetras and dwarf cichlids and small cichlids need a careful pairing, and loricariids (suckermouth catfish) range from tiny to very large, so check the adult size of the species you buy.
Keeping Penguin Tetras Together
Keep a school of at least 6 penguin tetras, and preferably 10 or more. A larger school spreads out any nipping and keeps the fish calmer.
Diet
In the wild, penguin tetras eat small crustaceans, insects, larvae, and worms. In an aquarium they accept flake, micro pellets, and freeze-dried food, and they enjoy small live or frozen foods like bloodworms, daphnia, and brine shrimp.
They are omnivores, so include some plant-based food too. Feed small amounts two or three times a day, giving only what they finish in about two to three minutes. Overfeeding fouls the water, which penguin tetras tolerate poorly.
Care
Regular water changes and testing keep penguin tetras healthy. Pair them with peaceful fish of similar size and keep a proper school to reduce stress.
Like most fish, penguin tetras can catch ich (also called ick) and gill and skin flukes. Ich is a parasite that shows as white spots, and it can be fatal if not treated. Quarantine the affected fish and treat with an ich medication.
Gill and skin flukes cause scratching, clamped fins, rapid breathing, and sometimes damaged fins or gills. In both cases, fish rub against objects in the tank. You can treat flukes with an anti-parasite product labeled for fish.
Other warning signs include refusing food, hiding, and fish that separate from the group. Test the water first.
Breeding
Penguin tetras are egg scatterers, and the parents will eat the eggs, so breed them in a separate tank. A well-fed female gets visibly fuller before she spawns.
Spawning tanks should be soft and slightly acidic (around pH 6.0 to 6.5) and a little warmer, about 78–81°F. Use a mesh liner over the bottom so eggs drop through but the parents can’t reach them, or use spawning mops or fine-leaved plants.
Remove the adults as soon as you see eggs. A female can lay a large number of eggs, up to a few thousand in a spawn. The eggs hatch in about a day, and the fry are free-swimming in about four days. Start them on infusoria or other micro foods, then move to baby brine shrimp.
Are Penguin Tetras Suitable for your Aquarium?
A school of penguin tetras is a good fit for a planted community tank with peaceful, similar-sized fish. They are adaptable, active, and easy to feed.
Don’t buy them if your tank already has long-finned fish like bettas, angelfish, or fancy guppies, or if you can only keep a few of them. In a small group they are more likely to nip.
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