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