Common Goldfish

Pellets, flake, blanched veggies, frozen

A pond fish, not an aquarium fish. Grows to 12–18″. Massive bioload; will eat any tankmate small enough to swallow. Coldwater, incompatible with tropical species.

Common goldfish belong in a POND, not an aquarium. If you must keep one indoors: 75gal absolute minimum for a single fish, 150gal+ for a pair. Coldwater (60–72°F). NO heater. Massive over-filtration is non-negotiable; goldfish are pollution machines and produce more waste than any other commonly-kept aquarium fish. Bare substrate or large smooth rocks, they swallow gravel. No real plants (they eat or uproot everything); silk or weighted plastic instead. Industrial-grade canister or sump filter rated for 2× the tank volume.

Always hungry, always looking. Goldfish recognize their keeper, learn to take food from hands, and develop genuine personalities, they're famously interactive. Constantly rooting through substrate. Will eat ANYTHING that fits in their mouth: small fish, snails, shrimp, plants. Active swimmers (single-tail varieties especially), they need horizontal swimming room more than depth.

Spawn in spring in ponds after a winter chill. In tanks: drop temperature gradually to ~55°F for 6 weeks (simulating winter), then raise to 68°F + add spawning mops. Males chase females; eggs scatter and stick to plants/mops. Remove parents IMMEDIATELY after spawning, they will eat every egg. Eggs hatch in 4–7 days; fry need infusoria then microworms then fine flake. Home goldfish breeding is rare; most fancy-goldfish breeders work outdoors in temperature-controlled ponds.

Common issues: swim bladder disease (overfeeding floating food, fast 3 days then peas), ich (white spots, raise temp to 78°F for 10 days, NOT higher; coldwater fish stress in warm water), fin rot (poor water quality), 'flipover' from genetics or injury. Goldfish live 15–25 years with proper care. A 2-year-old goldfish in a small bowl is dead from chronic stress, not old age.