Fancy goldfish

Quick facts

Adult size

20 cm

Lifespan

can live up to 15 years; well-kept fancies regularly reach 10-15 years; some documented past 20

Tank zone

all

Temperament

peaceful

Difficulty

intermediate

Water parameters

Temperature

18–24°C

pH

6.5 to 8.0

Hardness

5 to 20 dGH

Tank requirements

Minimum volume

120 L

Minimum length

80 cm

Flow

low

Lighting

any

Substrate

sand

Open swimming room

needed

Feeding

Diet: omnivore, feeds primarily at the all.

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.

Vegetable matter required (algae wafers, blanched zucchini, spinach).

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.

Habitat

Selectively bred from the same species as common goldfish (Carassius auratus) but with modified body shapes, fin types, and features. Major varieties include ryukin (deep body, humped back), oranda (wen growth on head), fantail (double tail), ranchu (no dorsal fin, rounded body), telescope eye (protruding eyes), pearlscale (domed scales), and bubble eye (fluid-filled sacs). Each variety has different swimming ability and fragility. All fancy goldfish are slower, less agile, and more delicate than common goldfish. They need cold-water conditions (18–24°C), no heater, and heavy filtration. The round body shape compresses the swim bladder and digestive tract, which causes the buoyancy and digestive problems the group is known for.

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

Bioload coefficient: 8.0 (extremely high waste producers relative to body size; goldfish lack a true stomach and pass food quickly, producing more ammonia per gram than most tropical fish).

Bioload coefficients are calibrated against the neon tetra as the anchor (1.0). See the methodology page for the formula and how each value was derived.

Further reading

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