Carassius auratus, the goldfish, is a social freshwater fish with care needs that vary between streamlined single-tail forms and rounded fancy varieties. These long-lived fish need spacious, well-filtered accommodation rather than bowls, and their adult size matters more than their size at purchase.

Key facts

• Origin: East Asia; goldfish were domesticated in China and are now bred worldwide.
• Adult size: commonly 15–25 cm for fancy varieties and 25–35 cm or more for common and comet goldfish, depending on variety and conditions.
• Temperature range: around 18–24°C is a practical aquarium range for most varieties. Streamlined forms tolerate cooler water better than many delicate fancy varieties.
• pH range: approximately 6.5–8.0; stable conditions are more important than chasing a precise reading.
• Minimum tank size: as a practical starting point, allow at least 150 litres for two small fancy goldfish, with room to upgrade as they grow. Adult common and comet goldfish need substantially larger, long aquariums or a suitable pond.
• Temperament: generally peaceful and sociable, but may swallow fish small enough to fit in their mouths.
• Diet: omnivorous; offer a quality goldfish food alongside suitable vegetables and occasional small aquatic invertebrates.

Keeping tips

• Cycle the aquarium before stocking. Use effective biological filtration and test regularly: ammonia and nitrite should remain at zero.
• Change around 30–50% of the water weekly as a starting routine, adjusting to stocking and test results. Treat replacement tap water for chlorine and chloramine, and avoid sudden temperature changes.
• Provide plenty of swimming space and good surface movement for oxygen exchange. Avoid sharp decorations, especially with telescope-eyed or long-finned varieties.
• Keep goldfish with compatible goldfish. Fast common and comet forms can outcompete slower fancy varieties at feeding time, so group fish with similar swimming ability.
• Feed small, measured portions and remove leftovers. For shop stock, quarantine new arrivals separately where possible and check that each fish swims comfortably and feeds normally.

Plan for adult size from the outset, and goldfish can make rewarding long-term aquarium residents. InternetZoo™ is a marketplace where Carassius auratus can be sourced by Latin name from breeders, farms and exporters.

See live Carassius auratus listings on InternetZoo™ — every listing is organised by its Latin name, so you always get the species you asked for.