Fancy goldfish

Water parameters

Tolerated range for this species. Aim for the middle of each band rather than the extremes.

Tank and habitat

Substrate: sand.

Behavior

Plant interaction: destroys most plants.

Feeding

Sinking pellets are strongly preferred over floating food. The round body shape makes surface-feeding difficult and increases air intake, which worsens swim bladder issues. Gel food (Repashy, homemade) is ideal because it sinks and is easy to digest. Blanched peas (shelled) 1-2 times per week aid digestion and help prevent constipation. Frozen bloodworm and brine shrimp for protein. Do not overfeed; fancy goldfish have compressed digestive tracts and are prone to blockages. Two small feedings per day, only what they consume in 1-2 minutes.

Compatibility

• Keep only with other fancy goldfish of similar swimming ability. Do not mix with common goldfish, comets, or shubunkins; slim-bodied fish outcompete fancies for food.
• Do not mix extreme varieties (bubble eye, celestial) with faster fancies (ryukin, oranda). The slower fish will starve.
• Not tropical. Do not house with tropical fish.
• Mystery snails and nerite snails are safe companions. Some keepers add weather loaches, which tolerate the same cool temperatures.
• Goldfish produce enormous waste. Filtration rated for 2-3x the tank volume is standard. Weekly 30-50% water changes minimum.

Origin and habitat

Fancy goldfish are ornamental forms of Carassius auratus, domesticated in China from crucian carp. Gold and red colour variants of the normally drab carp were noticed as early as the Jin dynasty, and deliberate selection for prized forms expanded under the Tang, giving the species well over a thousand years of breeding history. A 2020 PNAS genome study by Chen and colleagues resequenced 185 goldfish varieties alongside wild crucian carp and reconstructed that long history of selection, even linking a classic transparent-scale trait recorded since 1579 to a single gene. The fancy forms span a wide range of body and fin shapes: ryukin with a deep humped body, oranda with a fleshy head growth, fantail with paired tails, ranchu and lionhead with no dorsal fin, telescope eye with bulging eyes, and bubble eye with fluid-filled sacs beneath the eyes. Adult size depends on the variety, from roughly 15 cm to 30 cm or more, and records list a maximum length near 59 cm for large feral forms of the species. Every fancy shape swims poorly next to a slim-bodied goldfish, which is the root of most stocking problems, since fancies cannot keep up at feeding time. They are cold-water fish that do best below tropical temperatures and need no heater. With good care they live well past ten years; Records show a maximum age around 41, and the Guinness-recognised oldest goldfish, a fish named Tish, reached 43.

Breeding

Goldfish are egg scatterers that spawn as the water warms, usually around 18 to 24 C. Ready males develop small white breeding bumps, called tubercles, on the gill covers and along the first ray of the pectoral fins, and they chase the female persistently until she releases eggs for the male to fertilise. There is no parental care, and the adults will eat both eggs and fry, so a breeding tank with dense plants or a spawning mop helps some survive. Eggs hatch in roughly two to three days. The fry start out a drab brownish colour like their wild ancestors and can take up to a year to develop adult colours. Not every fry grows into the correct body shape for its variety, so serious breeders cull heavily, and crossing different fancy varieties gives unpredictable results.

Common problems

Swim bladder disorder is the signature health problem of fancy goldfish. Selection for a short, rounded body and curved spine compresses and deforms the swim bladder, so affected fish float at the surface, sink to the bottom, or roll upside down. Diet and overfeeding, poor water quality, sudden temperature changes, and the underlying body shape itself all contribute, which is why deep-bodied varieties such as ryukin and pearlscale are most prone. A common first response is to fast the fish for a few days and then offer shelled, cooked peas. Other recurring issues track back to water quality and anatomy: dropsy, with fluid swelling that lifts the scales into a pinecone shape, is often fatal; fin rot follows ammonia exposure or fin damage; and the exposed eyes of telescope and bubble eye fish are easily injured and infected. In orandas the head growth can eventually crowd the eyes.

Bioload

Further reading

• How to cycle a fish tank
• Stocking ideas by tank size