Not furry, but we like them anyway.
Royal Tetra
Inpaichthys kerri
Also called Blue emperor tetra, Purple emperor tetra, Regal tetra, Black emperor tetra
A peaceful little tetra that suits a calm community.
| Size | Small |
|---|---|
| Length | 2.8 to 3.5 cm (1 to 1 in)12 |
| Coat | Small scaled characin (tetra) with an adipose fin |
| Origin | South America: the Rio Aripuanã and upper Rio Madeira basins in Mato Grosso, Brazil123 |
| Last checked | 2026-09-30 |
Personality what they are like
A peaceful little tetra that suits a calm community. Rival males show off to each other, which brings out their best colours, but they do not cause trouble.21
The care rhythm a typical week and year
A typical home-care rhythm for a Royal Tetra. A starting point, not a vet's advice.
- FeedingSmall amounts once or twice a dayevery day
- Temperature checkevery day
- Water changeAbout 25% of the waterevery week
- Water testevery week
- Glass cleanevery week
- Filter rinseRinse in old tank water, never tap waterevery month
Looks how to spot one
Small scaled characin (tetra) with an adipose fin
A small tetra that looks a lot like the emperor tetra, with a dark band along the body and blue to purple sheen on males. The easiest way to tell the sexes apart is the little adipose fin: blue in males and mostly red in females. Females are also stockier and less colourful.23
Daily activity how busy a day looks
Moderately active; it swims in the middle of the tank and enjoys calm water with plant cover.2
Grooming and care the hands-on bits
Easy in soft, slightly acidic, clean water with regular partial water changes. It does best away from hard, alkaline water.21
Home where they are happiest
Tank of at least 60 x 38 x 30 cm (about 68 litres) for a small group. Water 24-27 °C, pH 5.5-7.0 (FishBase lists 6.0-8.0, but Seriously Fish notes it prefers acidic water), hardness 1-12 dGH. Tannin-stained water, plants and wood mimic its forest-stream home.21
Food basics what goes in the bowl
Accepts most prepared foods; regular small live or frozen foods such as brine shrimp and Daphnia help colour and growth.21
Company who they like around
Keep at least 6. Good with South American tetras, pencilfish, hatchetfish, dwarf cichlids, Corydoras and Otocinclus.21
The story where it all began
Géry and Junk described the royal tetra in 1977 from the Aripuanã river system in Brazil. Its species name honours Brazilian geneticist and entomologist Warwick Estevam Kerr. For a long time it was the only species in its genus.31
Fun facts for the dinner table
- 1
It is named after Warwick Estevam Kerr, a Brazilian geneticist and bee researcher.3
- 2
It looks very like the emperor tetra but can be told apart because it has an adipose fin.2
- 3
Males have a blue adipose fin and females a red one.2
- 4
In the wild it lives in slow, tea-coloured forest streams off the main river channels.2
Recognised by the official bits
- IUCN Red List
- Least Concern (assessed 7 November 2018)1
- FishBase
- Used commercially in the aquarium trade1
Owner questions the things everyone asks
How often should I feed my Royal Tetra?
Feed small amounts once or twice daily. Pet Wiki's starting plan suggests daily feeding, and they accept most prepared foods with occasional live or frozen treats for colour and growth.21 Pet Wiki plan
What does a Royal Tetra eat, and what should it never eat?
They eat most prepared foods and enjoy small live or frozen foods like brine shrimp and Daphnia. There is no specific list of forbidden foods in our sources, so ask a vet or good breeder about any items you are unsure of.21
How much space does a Royal Tetra need?
A tank of at least 60 x 38 x 30 cm (about 68 litres) is recommended for a small group. They are active middle-swimmers and appreciate room to move.21
What temperature, light or water does a Royal Tetra need?
Keep water at 24, 27°C, pH 5.5, 7.0 (preferring acidic side), and hardness 1, 12 dGH. They enjoy tannin-stained water with plants and wood, and subdued lighting that mimics a forest stream.21
How often should I clean a Royal Tetra's home?
Pet Wiki's plan suggests a weekly 25% water change, weekly glass cleaning, and a monthly filter rinse using old tank water. Regular partial water changes keep the soft, slightly acidic water they love.2 Pet Wiki plan
Can a Royal Tetra live with others?
Yes, they are peaceful and do best in a group of at least six. Good tankmates include South American tetras, pencilfish, hatchetfish, dwarf cichlids, Corydoras, and Otocinclus.21
How long does a Royal Tetra live?
Lifespan is not specified in our sources, so it varies. Ask a good breeder or an exotic-pet vet for typical longevity under proper care.
Can I handle a Royal Tetra?
Handling is not recommended for fish; it causes stress and can damage their delicate scales. Enjoy them from outside the tank.
Written from the sources on this page, a few checked guides (VCA, ASPCA, RSPCA) and Pet Wiki's own starting care plan. A friendly guide, not a vet's advice.
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Penguin TetraWhere this comes from
Every fact on this page has a numbered source. Spotted an error? support@petwiki.app.
- FishBase species summary: Inpaichthys kerri fishbase.seused for describer, maximum length, distribution, water range, IUCN status
- Seriously Fish species profile: Inpaichthys kerri seriouslyfish.comused for aquarium care, water parameters, behaviour, diet, sexing, habitat
- Wikipedia: Inpaichthys kerri en.wikipedia.orgused for other names, taxonomy history, etymology
Checked 2026-09-30. Text is written in our own words from these sources.