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

Selectively bred from Carassius auratus, a carp native to East Asia (EPFL), domesticated in China. The PNAS goldfish genome paper (Chen et al. 2020) confirms over 1,000 years of intensive domestication and selective breeding. Introduced to Europe in the late 17th century. The Japan introduction is placed around the late 16th century. The PNAS genetics study divides goldfish into three major lineages: Common Goldfish (CG), Wen Goldfish (WG, with dorsal fin and head growths like oranda), and Egg Goldfish (EG, without dorsal fin, like ranchu and lionhead). Modern fancy varieties include ryukin (deep body, humped back), oranda (wen head growth), fantail (double tail), ranchu (no dorsal fin), telescope eye (protruding eyes), and bubble eye (Biology Insights). Each variety carries morphological modifications that make them poor swimmers compared to slim-bodied goldfish; this is the key compatibility issue: fancy goldfish cannot compete with fast fish for food. Biology Insights reports lengths of 15-45cm depending on variety. The oldest recorded goldfish lived to 49 years, though most household goldfish live only six to eight years due to inadequate care. Cold-water fish; they do not require a heater and prefer cooler temperatures than tropical species.

Breeding

Same as common goldfish: egg scatterer triggered by temperature increases. Males develop breeding tubercles on gill covers and pectoral fins. Spawning is vigorous and messy; the male chases the female around the tank for hours. Eggs stick to plants and surfaces. Fry are brown-black and take months to develop color. Not all fry of fancy varieties will develop the correct body shape; breeders cull heavily. Cross-breeding different fancy varieties produces unpredictable results.

Common problems

Swim bladder disorder is the defining health problem of fancy goldfish. The compressed body puts chronic pressure on the swim bladder, causing fish to float sideways, upside-down, or sink to the bottom. Triggered by constipation, overfeeding, or temperature swings. Treatment: fast for 2-3 days, then feed shelled peas. Recurring episodes are common in deep-bodied varieties (ryukin, pearlscale). Dropsy (fluid accumulation causing pinecone-like scale protrusion) is often fatal and caused by organ failure from chronic poor water quality. Fin rot from ammonia buildup. Eye infections in telescope and bubble eye varieties, which have exposed or protruding eyes vulnerable to injury and infection. Wen overgrowth in orandas can block vision and requires careful trimming.

Bioload

Further reading

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