Moderate-high (heavy waste, frequent water changes)
Cost
Medium
Overview
The common goldfish is a coldwater fish descended from wild Asian carp, not a disposable bowl fish.
Kept properly, single-tail goldfish reach 20-30cm and commonly live past 15 years, with pond fish sometimes exceeding 25.
They are hardy and personable, but their adult size and heavy waste output make them more demanding than their low price suggests.
They belong in large aquaria or, ideally, garden ponds.
Housing
Goldfish are coldwater fish that thrive at roughly 18-22C with no heater needed; single-tails do well in unheated rooms or outdoor ponds and tolerate seasonal cooling.
Provide a fully cycled tank of at least 280L for one fish, adding around 75L per additional goldfish, with strong filtration sized above the rated load.
Keep ammonia and nitrite at zero and nitrate below 40ppm; a pH of 7.0-8.0 suits them.
Avoid sharp decor, do weekly 30-50% water changes, and never use a bowl, which stunts and kills them.
Diet
Goldfish are omnivores prone to obesity and constipation, so feed a quality sinking goldfish pellet as the staple plus plenty of blanched vegetables such as peas, spinach and courgette.
Pre-soaking dry food helps, as gulping air at the surface can contribute to swim-bladder problems.
Feed small amounts once or twice daily, only what they finish in a couple of minutes.
Avoid high-protein tropical foods and overfeeding, the leading cause of disease and fouled water in this heavy-waste species.
Health
Goldfish are hardy but pollution-sensitive, and commonly suffer ammonia poisoning, fin rot, ich and swim-bladder problems, nearly all traceable to undersized tanks, poor filtration or overfeeding.
Watch for clamped fins, gasping at the surface, or floating and sinking abnormally.
Maintain clean water and stable temperature to prevent most issues.
Quarantine new fish for 2-4 weeks, and treat ich with appropriate medication.
A varied diet and roomy housing keep them healthy for many years.
Temperament
Goldfish are peaceful, curious and trainable, learning to beg at feeding time and recognise their keepers.
They are social and do best in small groups of their own kind rather than alone.
Keep them only with other goldfish or similarly cool, slow swimmers; they will outcompete or eat tiny tankmates and are too messy for delicate community fish.
Mixing fast single-tails with slow fancy varieties is unwise, as commons outcompete fancies for food.
Advanced
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Intermediate