Goldfish

Also known as: Carassius auratus

Goldfish (Carassius auratus) are domesticated variants of the Prussian carp, selectively bred for over 1,000 years for color, fin shape, and body form. The Goldfish originates from East Asia, native to rivers, lakes, and ponds in China, Korea, and Japan; introduced worldwide through ornamental trade., reaches Adult size: 15-30 cm in captivity, typically lives 10-15 years on average, with well-cared specimens living 20+ years., and is kept at 18-24°C (65-75°F); tolerate cooler temps down to 10°C (50°F) but avoid sudden fluctuations.. Individual fish vary, so treat this as a general guide rather than a guarantee.

Key facts

Lifespan: 10-15 years on average, with well-cared specimens living 20+ years.
Adult size: Adult size: 15-30 cm (6-12 inches), with some varieties reaching up to 40 cm (16 inches) in optimal conditions.
Temperament: Peaceful and social; best kept in groups of 3-5 individuals; non-aggressive but may outcompete slower tankmates for food.
Minimum tank: Minimum 75 liters (20 gallons) for a single fancy goldfish; 115 liters (30 gallons) recommended for common goldfish; add 40 liters (10 gallons) per additional fish.
Water temperature: 18-24°C (65-75°F); tolerate cooler temps down to 10°C (50°F) but avoid sudden fluctuations.
pH range: 6.5-8.0; stable pH is more critical than exact value.

Species at a glance

Origin: East Asia, native to rivers, lakes, and ponds in China, Korea, and Japan; introduced worldwide through ornamental trade.
Adult size: Adult size: 15-30 cm (6-12 inches), with some varieties reaching up to 40 cm (16 inches) in optimal conditions.
Life span: 10-15 years on average, with well-cared specimens living 20+ years.
Temperament: Peaceful and social; best kept in groups of 3-5 individuals; non-aggressive but may outcompete slower tankmates for food.
Tank size: Minimum 75 liters (20 gallons) for a single fancy goldfish; 115 liters (30 gallons) recommended for common goldfish; add 40 liters (10 gallons) per additional fish.
Water temp: 18-24°C (65-75°F); tolerate cooler temps down to 10°C (50°F) but avoid sudden fluctuations.
pH range: 6.5-8.0; stable pH is more critical than exact value.
Diet: Omnivorous; require high-fiber, low-protein diet: 60% plant-based (blanched peas, spinach, zucchini), 30% high-quality sinking pellets, 10% live/frozen treats (brine shrimp, daphnia) 2-3x weekly.
Other names: Carassius auratus

About the Goldfish

Goldfish (Carassius auratus) are domesticated variants of the Prussian carp, selectively bred for over 1,000 years for color, fin shape, and body form. They are coldwater fish that thrive in temperate environments and do not require heaters in most climates. Known for their intelligence, they can recognize owners and learn feeding routines. Despite their hardy reputation, they produce significant waste and require robust filtration to maintain water quality.

Lifespan and health

With optimal care, goldfish commonly live 10-15 years, and documented cases exceed 20 years in spacious ponds or large tanks with pristine water quality. Lifespan is heavily influenced by genetics (common goldfish outlive fancy varieties due to less extreme body shaping), diet (overfeeding protein causes fatty liver disease), and water quality (chronic ammonia exposure reduces lifespan by 50% or more). Common health issues include swim bladder disorder (affects 30-40% of fancy goldfish, often from overfeeding or constipation; treat with 3-day pea fast and Epsom salt bath), ich (white spot disease, treat with 25°C/77°F temp increase and copper-free medication for 10 days), and fin rot (caused by poor water; treat with 50% water change and antibacterial medication). Preventive care includes avoiding overstocking (max 1 fish per 40L/10G), using UV sterilizers to reduce pathogens, and quarantining new fish for 4-6 weeks.

Overview

Care and tank setup

Tank setup requires a minimum 75L (20G) for one fancy goldfish, with strong filtration rated for 2x tank volume (e.g., 150L/40G filter for 75L tank) due to high bioload. Use smooth gravel or sand substrate to prevent injury to delicate fins; avoid sharp decorations. Provide moderate lighting (8-10 hours/day) and include hardy plants like Anubias or Java fern that can withstand nibbling. Water parameters must be maintained with weekly 25-30% water changes; test ammonia and nitrite levels twice weekly, keeping both at 0 ppm, and nitrate below 20 ppm. Feed 2-3 times daily, offering only what fish consume in 2 minutes; remove uneaten food within 5 minutes to prevent pollution. Tankmates should be other goldfish of similar size and swimming ability; avoid tropical fish, fin-nippers, or aggressive species like cichlids. Never keep with invertebrates like shrimp or snails, as goldfish will eat them.

Adding a Goldfish? Research the species’ adult size and temperament carefully, quarantine new fish before introducing them to your tank, and buy from reputable aquarium stores or breeders.

Sources

Breed information on this page is based on the Wikipedia article on the Goldfish, supplemented with additional research. Reviewed for accuracy.