About Common Goldfish
The Common Goldfish is the original goldfish variety - a hardy, streamlined fish that closely resembles its wild carp ancestors. Unlike fancy goldfish, Commons have a single tail, torpedo-shaped body, and are powerful swimmers. They are among the hardiest aquarium fish available, tolerating a wide range of conditions, but they grow surprisingly large (12+ inches) and produce significant waste. Common Goldfish are not suitable for bowls or small tanks and require proper filtration. They are coldwater fish that do best in unheated aquariums or outdoor ponds. Their fast swimming and large size make them incompatible with slower fancy goldfish varieties.
Care Guide
Care Requirements
Tank Setup
Common Goldfish need substantial space for their size:
- Minimum 30 gallons for one juvenile (55+ for adults)
- Add 10 gallons per additional fish
- Pond is ideal for mature fish (100+ gallons)
- Large canister filter (they are extremely messy)
- No heater needed (coldwater fish)
- Large surface area for oxygen exchange
- Smooth decorations (avoid sharp edges)
- Sand or smooth gravel substrate
- Open swimming space - they need room to swim
Important: Common Goldfish are fast swimmers that need long tanks rather than tall ones. They will outcompete fancy varieties for food.
Water Quality
- Temperature: 65-75°F (18-24°C) - room temperature is ideal
- pH: 7.0-8.4 (prefer slightly alkaline)
- Water Hardness: Moderate to hard (8-20 dGH)
- Ammonia/Nitrite: 0 ppm (extremely sensitive to ammonia)
- Nitrate: <40 ppm
Maintenance:
- Weekly 30-50% water changes
- Heavy filtration maintenance
- They produce massive amounts of waste
- Monitor ammonia levels closely - zero tolerance
Feeding
Common Goldfish are omnivores but need plant matter:
- High-quality sinking goldfish pellets (sinking prevents air ingestion)
- Vegetables: Blanched peas, zucchini, spinach, lettuce, cucumber
- Protein: Frozen bloodworms, brine shrimp (occasional)
- Flake foods: high-quality goldfish flakes
- Avoid: Tropical fish flakes (wrong nutrient balance)
Feeding Schedule: 2-3 times daily, only what they can eat in 2-3 minutes.
Important: They have huge appetites. Overfeeding leads to poor water quality.
Behavior & Compatibility
Active swimmers that need appropriate tankmates:
- Best With: Other Common or Comet Goldfish (similar speed and size)
- Can Work With: Dojo Loaches, White Cloud Mountain Minnows (in coldwater tanks)
- Never With:
- Tropical fish (temperature mismatch)
- Fancy goldfish (will outcompete for food, stress them out)
- Small fish (temperature mismatch)
Behavior: Constant swimmers always exploring. Active and interactive with owners.
Common Health Issues
- Swim Bladder Disease: Often from constipation or overeating; feed peas
- Ich: White spots; raise temperature slightly and treat
- Fin Rot: From poor water quality; improve maintenance
- Dropsy: Bloated with raised scales; often fatal
- Ammonia Poisoning: Lethargy, red gills; immediate water change needed
Size & Growth
Common Goldfish grow large and live long:
- First year: Can reach 4-5 inches
- Mature size: 10-14+ inches
- Weight: Can reach 1+ pound in ponds
- Lifespan: 10-20 years (some live 30+ years in ponds)
Never keep in bowls - this severely stunts growth and causes deformities.
Tank Maintenance
Due to their extreme waste production:
- Weekly 30-50% water changes
- Heavy gravel vacuuming
- Clean canister filter monthly
- Test water parameters weekly
- Monitor for signs of ammonia poisoning
Tips for Success
- Buy the largest tank possible from the start
- Invest in oversized, quality filtration
- Feed sinking pellets to prevent swim bladder issues
- Provide vegetable matter regularly
- Never mix with tropical fish
- Never mix with fancy goldfish (speed mismatch)
- Quarantine new fish for 2-4 weeks
- Keep only with similar single-tail varieties
- Consider upgrading to a pond as they mature
- They are jumpers - secure lid essential
Comparison to Fancy Varieties
Key differences from fancy goldfish:
- Common: Single tail, streamlined body, fast swimmer, hardier, 12+ inches
- Fancy: Double tail, round body, slow swimmer, more delicate, 6-8 inches
Never mix Common and Fancy goldfish - Commons will outcompete them for food and stress them.
Outdoor Pond Considerations
Commons are excellent pond fish:
- Minimum pond size: 100+ gallons for a few fish
- Depth: 2+ feet for temperature stability
- Filtration: Essential - they produce lots of waste
- Winter: Can survive under ice if pond is deep enough
- Predators: Protect from herons, raccoons, cats
- Lifespan: Often 20+ years in proper ponds