Common Goldfish Care Guide - Aquarium Setup, Diet & Breeding

Common Goldfish are the familiar single-tailed form of Carassius auratus, with a deep-bodied shape, bright orange-gold colouration and a long, streamlined tail. Selectively bred varieties may also appear yellow, white, red, black or calico, although the traditional common form has a relatively simple body and finnage compared with fancy goldfish.

The Common Goldfish is descended from Carassius auratus populations native to eastern Asia, especially China. The species has been domesticated for centuries and is now established in many countries through the aquarium and ornamental pond trade.

A single Common Goldfish needs at least 150 litres, with roughly 75 additional litres for each extra fish; a pond is often the most suitable long-term home as adults become large and produce substantial waste. Use a tank at least 120 cm long for one young fish, increasing the footprint substantially as it grows, with powerful biological filtration and good surface movement. Choose smooth gravel or sand, leave generous open swimming space, and use sturdy plants, rounded stones and ornaments without sharp edges that could damage the fins.

Up to around 30 cm (12 in) in captivity, although exceptional pond-kept fish may grow larger. Females are often slightly longer and heavier-bodied than males, particularly when carrying eggs.

Common Goldfish are omnivores and should receive a varied diet based on a quality goldfish pellet or flake, supplemented with blanched leafy vegetables such as spinach, peas or courgette. Frozen or live foods, including bloodworms, daphnia and brine shrimp, can be offered occasionally. Feed sensible portions and avoid relying on bread or other unsuitable human foods.

The safest companions are other Common Goldfish and similarly sized, peaceful single-tailed goldfish. In large ponds, they may also be kept with robust, temperate species such as weather loaches, provided their environmental needs match. Avoid tropical fish, fin-nippers, highly aggressive species and very small fish that may be swallowed; fancy goldfish can also be disadvantaged by the faster swimming and more competitive common form.

Common Goldfish are egg scatterers that typically breed when temperatures rise after a cooler period. Provide mature males and females with abundant oxygenation, fine-leaved plants or spawning mops, and plenty of swimming space. Males chase females and fertilise the eggs as they are released. Adults should be removed after spawning because they readily eat the eggs; hatching usually occurs within several days, and the fry need very small foods before progressing to baby brine shrimp and appropriately sized prepared diets.

Mature females are usually broader through the abdomen and have a rounder body profile, while males tend to be slimmer. In breeding condition, males may develop small white breeding tubercles on the gill covers and leading edges of the pectoral fins, and may chase females persistently.