Goldfish

The goldfish is the world's oldest ornamental fish, first selectively bred from wild carp in ancient China more than 1,000 years ago. They were introduced to Japan in the 16th century and to Europe in the 17th century, eventually becoming the world's most popular pet fish.

Goldfish are coldwater fish and do not require a heater in most Australian homes. They are hardier than many aquarium fish but have been significantly undersized and under-filtered in traditional keeping. The fishbowl is now widely condemned as inadequate by welfare organisations and experienced aquarists. Goldfish require proper filtration, adequate space and regular water quality management. Properly kept, they can live 20+ years and are genuinely long-term pets.

The most important rule in goldfish keeping is that bowls are not appropriate housing. Goldfish produce significant waste, consume substantial oxygen, and grow large. Minimum tank size for the first two goldfish (5 cm or smaller): 20 litres. Add at least 10 litres for each additional goldfish. As the goldfish grow, they will require a significantly larger tank to accommodate their full adult size.

Once your goldfish have matured, the minimum recommended tank size is 80 litres for one to two single-tailed goldfish, with at least 40 additional litres for each extra fish. Single-tailed varieties generally thrive best in outdoor ponds due to their size and activity level.
For fancy goldfish varieties, a tank of 80–150 litres is recommended for two to three fish, with at least 40 additional litres for each extra fish.

Robust filtration is essential: a filter rated for twice the tank volume is a minimum. Substrate should be rounded pebbles or fine gravel. Temperature range is 10-24ºC; no heater is needed in most Australian homes but protection from extreme cold (below 5ºC) is required in cold climates.

Goldfish are omnivores preferring vegetable matter. The primary diet should be quality goldfish-specific pellets or flake. Sinking pellets are preferable for fancy varieties to prevent ingesting air at the surface, which contributes to buoyancy problems. Feed once to twice daily; offer only what is consumed in two to three minutes. Overfeeding causes water quality problems and swim bladder disorders.

Supplement with blanched peas (skins removed) weekly or twice weekly: this is one of the most important preventative measures for the swim bladder problems common in fancy varieties. Blanched spinach, zucchini, lettuce and cucumber are also accepted. A one-day fast per week maintains digestive health.

Goldfish are opportunistic feeders and will attempt to eat anything that fits in their mouths. When keeping goldfish with other cold-water species, be mindful of size differences. A good general rule is: if it fits in a goldfish's mouth, it may eventually be eaten.

Goldfish should be handled only when medically necessary. Use a soft, fine-mesh net and minimise time out of water. Hand-feeding by holding food at the water surface is a gentle, low-stress form of interaction. Never combine single-tailed and fancy varieties: single-tails bully fancies and monopolise food.

They are peaceful community fish compatible with other goldfish and compatible coldwater species. They are curious explorers of their environment.

Goldfish benefit from a varied environment. Provide aquarium plants (live or artificial) and smooth-edged decor for exploration. Feeding enrichment with varied food items presented in novel ways (clipped blanched lettuce, floating blanched pea) encourages natural foraging. For pond goldfish, natural live food (daphnia, mosquito wrigglers) provides the most biologically relevant enrichment.

Swim bladder disorder: Very common in fancy goldfish, causing floating, sinking or tilted swimming. Often linked to overfeeding or feeding dry flakes. Prevention: use sinking pellets, offer blanched peas regularly, avoid overfeeding.

Ich (white spot): Common in stressed or newly introduced fish.

Fin rot: Bacterial erosion of fins caused by poor water quality.

Ammonia and nitrite toxicity: Lethargy, gasping at the surface, red streaks on fins; caused by insufficient cycling or overfeeding.

Constipation: Common in fancy varieties on pellet-only diets; prevented with vegetable supplementation.