Gold fish fantail

The Fantail Goldfish (Carassius auratus) is considered the foundational breed of "fancy" goldfish, celebrated for its characteristic egg-shaped body and elegant, flowing double tail fin. Because they lack the extreme structural modifications seen in other fancy breeds (like protruding eyes or large head growths), they are generally hardier, swim better, and make an excellent choice for beginner aquarists.

Breed Overview & Appearance

Body Type: Stout, egg-shaped body with a high dorsal fin and no shoulder hump.
The "Fantail": Features a quadruple caudal (tail) fin split into two matching, flowing halves.
Size: Typically grows between 6 to 8 inches (though they can reach up to 12 inches in ideal conditions).
Lifespan: Highly durable for a fancy breed, averaging 10 to 15 years—and sometimes up to 20 years with proper care.

Tank Requirements & Water Parameters

Because goldfish are high-waste producers, keeping their environment clean is the key to longevity.

Parameter	Recommended Level	Notes
Tank Size	20 gallons minimum for the first fish.	Add 10–20 gallons per additional fish. Horizontal tanks are preferred.
Temperature	65°F to 75°F (18°C–24°C).	Ideal range is 73°F–74°F (23°C). Avoid sudden drops.
pH Level	6.5 to 8.0.	Prefers stable, mostly neutral water.
Filtration	Heavy-duty mechanical & biological filtration.	Crucial to handle their high bioload and keep toxic ammonia at 0 ppm.
Substrate & Decor	Soft sand, smooth rocks, or large rounded gravel.	Avoid sharp objects; their slow swimming makes them prone to fin tearing.