Coldwater - Goldfish
The goldfish (Carassius auratus) is not just one of the more easily recognizable aquarium and pond fish. It also ranks as the most popular of all pets worldwide in numerical terms, with a population measured in billions. It is the goldfish’s adaptability and ease of care which has helped to ensure its massive following, although the surprisingly wide range of colors and varieties in which these fish now occur has also enhanced their appeal.

All today’s goldfish are descended from a dull, dark species of wild carp which lives in the waterways of southern China, where such fish are still caught for food. From about 800 AD onwards, some of these carp which had unusual orange markings started to be kept and bred selectively for their coloration. Before long, other characteristics such as different fin shapes and scale patterns also became established.

Goldfish were first brought to Europe around 1700s, but they appear to have remained unknown in the US up until 1874. They soon established a massive following though, with special goldfish farms being set up to meet the huge demand for them. There are now yellow, white, chocolate and black varieties of goldfish, as well as variegated forms with distinctive patterning, but body shape tends to be more significant than coloration in terms of distinguishing the different varieties.

Care needs

Within the home, goldfish do not need a heated aquarium, but even when small, they should be housed in a rectangular tank which provides plenty of space for swimming, rather than a goldfish bowl. They will grow rapidly and it will be false economy to purchase a tank less than 91cm (36in) in length. When designing the aquarium, do not clutter the available area with rockwork, curbing the swimming space for the fish.

Also, avoid any sharp-edged pieces, especially for varieties such as bubble-eyed goldfish which may injure themselves on such projections. Goldfish are relatively destructive in the confines of an aquarium, digging in the substrate and uprooting plants here, so these will need to be weighed down. A power filter, as well as an undergravel filter will help to keep the water clean. Regular partial water changes every three to four weeks are recommended.


Goldfish can only be sexed reliably when in breeding condition. The male fish develops white spots on the gill plates, extending along the pectoral fins on each side of the body, while the female swells with eggs. As the time for spawning approaches, he will chase her relentlessly. Unfortunately, unless the goldfish are removed from the aquarium immediately after spawning, their eggs and any fry which do hatch are likely to be eaten by the adult fish.

Hatching of the eggs depends on the water temperature, usually occurring within a few days in the home aquarium. Once the young fish start swimming, they should be offered a fry food at first, followed by powdered flake. It can take anywhere from several months onwards for the goldfish to gain their coloration. A few individuals may even remain blackish in colour, never undergoing this transformation. Their lifespan can average anywhere from 10-15 years, and may sometimes be much longer.Goldfish black and orange

At a glance

Water temperature: 10-25°C (50-70°F), but can survive at much lower temperatures.
pH: Relatively unfussy, but around neutral (pH 7.0) preferable.
Diet: Goldfish flake food and pellets.
Area of the tank: Instinctively frequents the lower level.
Compatibility: Tolerant towards other goldfish.