At a glance the quick version
Looks how to spot one
Scaled, twin-tailed fancy goldfish with a flat, butterfly-shaped tail
A rounded fancy goldfish, typically a telescope with globe-shaped eyes, whose wide double tail is spread out flat. Seen from above the tail opens like a pair of butterfly wings, a bit like a broadtail turned on its side.21
Personality what they are like
Peaceful and calm, a gentle swimmer best kept with other slow fancy goldfish.1
Daily activity how busy a day looks
Low to moderate. Appreciates open swimming space and gentle flow; a wide tank lets the tail be seen at its best.32
Grooming and care the hands-on bits
Needs a good filter, regular partial water changes with dechlorinated, temperature-matched water, and routine tests showing zero ammonia and nitrite. Smooth decor and soft or silk plants suit telescope-eyed fish.34
Home where they are happiest
Keep in a filtered aquarium, not a bowl. Aqueon suggests at least 40 litres (10 US gallons) per adult fancy goldfish, while the RSPCA advises at least 60 litres per goldfish, with wider tanks giving more stable water. Fancy goldfish are comfortable at about 20-23 °C (Aqueon gives 68-74 °F), and the RSPCA notes goldfish in general live at 10-21 °C without a heater. A pH of roughly 6.0-8.4 is fine (FishBase gives 6.0-8.0, Aqueon 7.0-8.4).435
Food basics what goes in the bowl
Omnivore. Offer a goldfish flake, granule or sinking pellet once or twice a day, only as much as is eaten in two to three minutes, with frozen or live foods as occasional treats.45
Company who they like around
Sociable; FishBase suggests goldfish in groups of five or more. Good companions are other telescope and slow fancy goldfish.51
The story where it all began
The butterfly tail describes a double tail that is flattened horizontally and looks its best from above. It is most associated with the telescope goldfish, a Chinese variety dating to the early 1700s.21
Fun facts for the dinner table
Recognised by the official bits
- Taxonomy
- Name for fancy goldfish whose double tail is flattened horizontally so that it looks like a butterfly from above; most often seen on telescope goldfish2
- IUCN Red List
- The parent species Carassius auratus is assessed as Least Concern5
The care rhythm Furry Diary remembers it for you
A typical home-care rhythm for a Butterfly Tail Goldfish. It is our own starting plan, not a vet's advice, and you can change every line in the app.
- Feedingevery day
- Water changeAbout 25 to 30% of the waterevery week
- Water testevery week
- Glass cleanevery week
- Filter rinseevery month
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Where this comes from
Every breed page shows where each fact comes from. If we got something wrong, sorry, we are pet people, not a science magazine. Tell us at support@furrydiary.app and we will fix it.
- Telescope (goldfish) - Wikipedia en.wikipedia.orgused for origin, colours, tankmates
- List of goldfish varieties - Wikipedia en.wikipedia.orgused for definition of the butterfly tail, body, history
- Fish environment - RSPCA rspca.org.ukused for tank size, filtration, water changes
- Goldfish Care Sheet - Aqueon aqueon.comused for temperature, tank size, diet
- Carassius auratus - FishBase fishbase.seused for pH, group size, diet, IUCN
Checked 2026-09-30. Text is written in our own words from these sources.