Goldfish
Common Name
Goldfish
Scientific Name
Carassius auratus
Carassius auratus
Adult Size
Fancy: 6–8 inches (15–20 cm) Common/Comet: 10–12 inches (25–30 cm); some up to 14 inches (35 cm)
Recommended Group Size:
2+
Experience Level:
Beginner
Recommended Aquarium Size
Goldfish are never appropriate for bowls or small tanks, contrary to popular imagery. They need substantial room to account for their active swimming, high waste output, and potential growth to sizes over 8–12 inches. A long, rectangular aquarium is preferred to provide ample swimming space
| Number of Fish | Minimum Tank Size | Notes |
|---|---|---|
| Single adult | 20 gallons | For fancy varieties |
| Additional | +10 gallons/fish | More for fast-growing, large-bodied breeds |
| Standard/comet | 40 gallons+ (per fish) | For single, up to 12" growth possible |
Compatible Tank Mates
Goldfish cannot inhabit mixed tropical community tanks; they are incompatible with most tropical species due to their cooler water preferences and messy, voracious nature
| Compatible Species | Notes |
|---|---|
| Other goldfish (similar type) | Only keep with other goldfish; avoid mixing single-tail with fancy breeds |
| White cloud mountain minnow | Tolerates cool water; suitable with small goldfish |
| Dojo/Weather loach | Only if kept at cooler temps, requires their own space |
| Snails (Mystery, Nerite) | May coexist, monitor for harassment |
| Avoid: tropical fish, shrimp, slow invertebrates, fin-nippers | Goldfish are coldwater, create too much waste, and may become aggressive or eat tankmates |
Goldfish are best kept with other goldfish of similar body type and swimming ability. Fancy varieties (like fantails, orandas, and ryukins) are slower and more delicate, while single-tail types (like commons and comets) are faster, more active, and often more boisterous. Mixing these types can lead to feeding competition, stress, and injury, so it’s important to match temperament and mobility.
A few coldwater-compatible species can coexist with goldfish under specific conditions. White cloud mountain minnows are small, peaceful, and tolerate cooler temperatures, making them suitable companions for juvenile or small fancy goldfish. Dojo or weather loaches are bottom-dwellers that thrive in similar conditions, but they require ample space and hiding areas to avoid stress. Snails like mystery and nerite species may coexist with goldfish, but interactions should be monitored closely — goldfish may nip at or harass slow-moving invertebrates.
Avoid housing goldfish with tropical fish, shrimp, slow invertebrates, or fin-nippers. Goldfish are coldwater fish that produce significant waste and may become aggressive or opportunistic feeders. Their cooler temperature requirements, messy eating habits, and tendency to root through substrate make them incompatible with most tropical community setups.
In short, goldfish do best in species-only tanks or with carefully selected coldwater companions. Always prioritize space, water quality, and behavioral compatibility when planning a mixed setup.
Water Parameters
Goldfish are giant waste producers. They demand strong filtration and frequent large water changes (50% weekly or more). They will thrive in a stable, unheated environment within the above range, but fancy breeds are less cold-tolerant than common or comet varieties and prefer low 70s°F
| Parameter | Range |
|---|---|
| Temperature | 65–75°F (18–24°C) |
| pH | 6.5–8.0 |
| Hardness | 5–19 dGH |
| Ammonia/Nitrite | 0 ppm |
| Nitrate | <20 ppm (ideally <10 ppm) |
| Filtration | Strong, overpowered |
History and Origin
Originally domesticated in China over a thousand years ago, goldfish descend from the wild Prussian carp. Their popularity spread through East Asia and then to Europe in the 17th century, resulting in vast array of body types, colors, and fin configurations (e.g., Black Moor, Oranda, Ryukin, Bubble Eye, Telescope Eye). Today, many fancy goldfish are incapable of surviving in the wild due to their extravagant shapes, poor swimming ability, and vulnerabilities. In the right environment, goldfish are intelligent, trainable, and long-lived
Temperament and Personality
Goldfish are curious, social, food-motivated, and active during daylight hours. They are generally peaceful but will compete vigorously for food and devour any smaller fish or invertebrates, including their own fry. Long-finned or slow fancy types can be bullied by faster, single-tail types—separation is preferred for mixed breeds. They can form routines and may recognize their caretakers, “begging” at the glass at feeding time
Other Pertinent Information
Diet: Omnivorous; feed sinking pellets/flakes, along with blanched vegetables (peas, spinach) and occasional high-protein treats (brine shrimp, bloodworms)
Tank Setup: Use smooth gravel or sand, large rocks or driftwood (well-secured), and consider plastic or robust live plants—goldfish will dig and may uproot softer species.
Maintenance: Goldfish stir up debris; use powerful filtration and frequent gravel vacuuming.
Health: Susceptible to fin rot, ich, swim bladder disease, and constipation; good water quality prevents most issues.
Reproduction: Spawn in spring; large numbers of eggs are laid on plants/substrate; parents will eat fry.
Lifespan: 10–15 years common, over 20–30 years possible with excellent care.
