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Goldfish

Carassius auratus

The long-lived coldwater classic that was never meant for a bowl

The goldfish (Carassius auratus) is a domesticated coldwater cyprinid that's been kept in home tanks for over a thousand years. Commons and comets are strong-swimming, foot-long fish that need pond-scale filtration to thrive; fancy varieties like the Oranda, Ryukin, and Black Moor stay smaller but are selectively bred for body shape over athletic ability. Despite their reputation as throwaway fair-prize fish, goldfish are social, intelligent, and routinely live 10–15 years when given the tank space, cool temperatures, and filtration they actually need.

46 articlesCare level medium
A fancy goldfish with a bright orange body and translucent white-edged fins, viewed head-on against a pure black background
Photo by Zhengtao Tang on Unsplash
VITAL STATS
Tank size
20 gallons (75 L) for one fancy, +10 gallons per additional; 75+ gallons (285+ L) for commons or comets
Temperature
18–22°C (65–72°F), coldwater — no heater
pH
7.0–8.4
Hardness
5–19 dGH, moderately hard to hard
Temperament
Peaceful, social, active
Diet
Omnivore; sinking gel food, goldfish pellets, blanched vegetables, occasional bloodworms
Max size
Fancy: 15–20 cm (6–8 in); Common/Comet: 25–35 cm (10–14 in)
Lifespan
10–15 years, 20+ possible
Origin
Domesticated in China from Prussian carp — over 1,000 years of selective breeding
Includes

Common Goldfish, Comet, Shubunkin, Fantail, Oranda, Ryukin, Black Moor, Ranchu, Lionhead, Telescope Eye, Bubble Eye, Pearlscale

01

Care

Goldfish care is mostly about unlearning what the toy aisle taught you: they aren't bowl fish, they aren't tropical fish, and they aren't small. This section covers the daily and weekly routine that keeps a goldfish thriving into its second decade — feeding, water changes, and the stocking math that keeps bioload manageable.

02

Tank Size

The single question that decides whether a goldfish lives or dies young is tank size. Fancy varieties need 20 gallons for one plus 10 per additional; commons and comets eventually need something closer to a pond. This section walks through why bowls and 5-gallon starter kits always fail and what footprint actually works.

03

Tank Setup

A well-set-up goldfish tank is long, heavily filtered, and stocked with the kind of decor that won't chip a fancy's wen or trap a bubble-eye. This section covers substrate choice, safe decor, lighting, and what to leave out.

04

Water Parameters

Goldfish are hard-water, neutral-to-alkaline fish that produce more ammonia per inch than almost anything in the hobby. This section covers ideal pH, hardness, and nitrate ranges, plus why water quality drives every other goldfish outcome.

05

Behavior

Goldfish are social, recognizable-to-their-keepers, and genuinely curious — not the blank-eyed memoryless fish of the 15-second-memory myth. This section covers what normal goldfish behavior looks like, how to read stress and contentment, and what their senses can actually detect.

06

Types

Goldfish are either common/single-tail (commons, comets, shubunkins) or fancy/double-tail (orandas, ryukins, black moors, ranchus, telescopes, bubble eyes, pearlscales). This section covers the major varieties, which ones are easiest to keep, and which types can coexist in the same tank.

07

Aquarium Plants

Goldfish are notorious plant-eaters — they'll graze, uproot, and dismantle soft-leaved plants in days. That doesn't mean a planted goldfish tank is impossible; it means the plant list is a short one of hardy, tough-leaved, or floating species. This section covers what survives, what doesn't, and how to set up a goldfish tank with live plants.