Goldfish care guide
Goldfish (Carassius auratus) — minimum tank 150 L, temperature 18-24 °C, pH 6.5-8.
Compiled by Aquairi from published sources · Published · Updated
Overview
The Goldfish (Carassius auratus) is a cyprinid fish domesticated in China over a thousand years ago from wild Asian crucian carp stock. Hundreds of selectively bred varieties exist, ranging from the slender Common and Comet forms to the rounded, double-tailed Ranchu, Oranda and Telescope-eye fancy types.
Taxonomy
- Family: Cyprinidae
- Genus: Carassius
- Scientific name: Carassius auratus
Habitat
Wild ancestors inhabit slow, well-vegetated freshwater of East Asia. Feral populations have established on every continent except Antarctica and are considered invasive in many countries. Goldfish tolerate a wide temperature range from cold to subtropical waters.
Tank requirements
- Minimum tank volume: 150 L (39.6 US gal)
- Adult size: 15-30 cm
- Temperature: 18-24 °C (64-75 °F)
- pH: 6.5-8
- GH: 5-20 °dGH
- Water flow: moderate
- Lifespan: 10-25 years
Diet
An omnivore, feeding on plant matter, detritus, insect larvae and small invertebrates. In aquaria a sinking goldfish-specific pellet supplemented with blanched vegetables (peas, spinach, cucumber) and occasional gel food prevents the swim-bladder issues common to round fancy forms.
Compatibility
Peaceful and social. Single-tailed goldfish (Common, Comet, Shubunkin) are active, fast and grow large; they suit ponds or very long tanks. Fancy double-tailed forms are slower swimmers and should not be combined with single-tailed types or with fin-nipping species; tropical fish are unsuitable due to differing temperature requirements.
Breeding
An egg-scatterer. Spawning is triggered by a temperature rise after a cool winter period; eggs are deposited on plants or spawning mops and parents readily consume them. Fry are dark-coloured and acquire adult colour after several months.
Conservation status
IUCN Red List: Least Concern. The domesticated population is essentially limitless; wild Carassius auratus remains common across its native East Asian range.
Bubble Eye Goldfish Breeding Guide
Overview
The bubble eye is a fancy variety of the goldfish, Carassius auratus, and reproduces by the same biology as all goldfish. It is an egg-scattering, oviparous spawner; the eggs are sticky and attach to water plants or submerged objects, and females release several batches of eggs across the season rather than a single clutch.
Sexing
Outside the breeding period the sexes look alike. As spawning approaches, males develop breeding tubercles, white pinhead-sized spots on the gill covers, head and sometimes the pectoral fins, while females in condition swell visibly with eggs.
Conditioning
Goldfish only reach sexual maturity with sufficient water volume and proper nutrition. Cool water over the winter months is needed for correct ova development, so a seasonal temperature cycle prepares breeders before the intended spawn.
Breeding Setup
Provide an adhesive-egg medium such as dense fine-leaved plants (Cabomba, Elodea) or a spawning mop, installed before spawning begins. Because the bubble eye carries fragile fluid-filled sacs beneath the eyes, the spawning container must be free of sharp or abrasive surfaces that could rupture them during the vigorous chase.
Spawning Behavior & Trigger
Spawning typically follows a marked rise in temperature in spring. At around 20-23 degrees C (68-73 degrees F) males chase gravid females from dawn to early afternoon, bumping and nudging them to release eggs that scatter onto the plants or mop and are then fertilised.
Egg & Fry Care
Remove the adults once spawning ends, as goldfish eat their own adhesive eggs, which cannot be relocated. Eggs hatch in about 48 to 72 hours (roughly four days), and fry become free-swimming around 24 hours later, when feeding starts with newly hatched brine shrimp or fine fry food. Fry assume their basic shape within a week or so but stay metallic brown like wild ancestors and may take a year to colour up.
Common Challenges
As a selectively bred variety, bubble eye fry must be graded and culled to retain the dorsal-less back and the paired eye sacs; only some of each spawn show the wanted form. Heavily modified fancy goldfish can lose the ability to spawn naturally due to altered body shape, and hand-stripping is sometimes used, though it can harm the fish if done incorrectly.
Celestial Goldfish Breeding Guide
Overview
The Celestial is a domesticated variety of Carassius auratus, distinguished by a double tail and a breed-defining pair of upturned, telescope eyes with pupils gazing skyward. Like all goldfish it is an egg-scatterer. The variety is produced by selective breeding, and some extreme fancy goldfish are much less hardy than forms closer to the wild original; the permanently skyward eyes leave the fish with very poor sight, so breeding requires close attention to feeding and tank-mate selection.
Conditioning
Goldfish reach sexual maturity only with sufficient water volume and the right nutrition. Mature, healthy adults are conditioned before the breeding season. The optimum temperature for goldfish is between 20 and 22 °C (68 and 72 °F); temperatures under about 10 °C (50 °F) are dangerous to fancy varieties and temperatures over 30 °C (86 °F) can also cause harm.
Breeding Setup
Provide dense aquatic vegetation such as Cabomba or Elodea, or a spawning mop, because the eggs are adhesive and attach to this material. A separate spawning tank lets the adhesive eggs be protected, as adults may eat young they encounter.
Spawning Behavior & Trigger
Breeding usually happens after a significant temperature change, often in spring. Males chase gravid females and prompt them to release their eggs by bumping and nudging them. The female then scatters adhesive eggs across the plants or spawning mop.
Egg & Fry Care
The eggs hatch within 48 to 72 hours. In their first weeks of life the fry grow quickly, an adaptation born of the high risk of being eaten by adult goldfish, other fish and insects. Within a week or so the fry begin to assume their final shape, although a year may pass before they develop mature goldfish color; until then they are a metallic brown like their wild ancestors.
Common Challenges
Selective breeding for the upturned celestial eyes leaves the fish with very impaired sight, which complicates feeding and competition at spawning. Some highly selectively bred goldfish can no longer breed naturally due to their altered shape, and heavy culling of fry is needed to keep only those that express the breed-defining double tail and skyward eyes.
Comet Goldfish (Carassius auratus) Breeding Guide
Overview
The Comet is a single-tailed variety of the goldfish, Carassius auratus, a member of the family Cyprinidae native to China. It was developed in the United States from the common goldfish by Hugo Mulertt in the 1880s and is distinguished by a long, single, deeply forked tail fin and a slimmer body than the common goldfish. Like other goldfish, it is an egg-scatterer that breeds readily, particularly in ponds and large tanks.
Sexing
Mature males develop breeding tubercles — small white, pimple-like bumps — on the gill covers and along the leading rays of the pectoral fins during the breeding season. These gradually disappear after spawning. Females are identified by a plumper, fuller body as they fill with eggs. Tubercles can occasionally appear on females, so they are not an absolute guide to sex.
Conditioning
Goldfish reach spawning condition with adequate space and good nutrition. A varied diet brings females into roe and prepares males to display tubercles. Comets are active fish best conditioned in spacious cool-water systems such as ponds or very large tanks.
Spawning Behavior & Trigger
Breeding usually follows a significant temperature change, often in spring. A simulated seasonal warming after a cool period is the typical trigger. During spawning, males chase the gravid female and prompt her to release eggs by bumping and nudging her, after which the eggs are fertilised in open water.
Egg & Fry Care
Goldfish eggs are adhesive and attach to dense aquatic vegetation such as Cabomba or Elodea, or to a spawning mop. Eggs hatch within 48 to 72 hours. Within a week the fry begin to assume their final shape, though a year may pass before they develop mature goldfish colour; until then they are a metallic brown like their wild ancestors. Fry grow quickly, an adaptation to the high risk of being eaten by adult goldfish, so separating eggs or fry from adults improves survival.
Common Challenges
Single-tail varieties such as the Comet are selectively bred for body and finnage, so rigorous fry selection (culling) is used to maintain type. Adults readily eat their own eggs and fry, making physical separation important.
Fantail Goldfish (Carassius auratus) Breeding Guide
Overview
The Fantail is a twin-tailed fancy variety of the goldfish, Carassius auratus (family Cyprinidae), originating in China and Japan. It has an egg-shaped body, a high dorsal fin and a long quadruple caudal fin whose double tail and anal fins are well divided into two matching halves. It is considered hardy and serves as the base for many fancy goldfish varieties, and is reported to be very easy to breed.
Sexing
As in all Carassius auratus, mature males develop breeding tubercles — small white pimple-like bumps — on the gill covers and leading pectoral-fin rays during the breeding season; these fade after spawning. Females become noticeably plumper as they fill with eggs. Because tubercles can occasionally occur on females, body shape and tubercles are best used together.
Conditioning
Fantails reach spawning condition with good space and nutrition. A varied diet conditions females into roe and prepares males. The ideal aquarium temperature for fantails is around 23 °C (73-74 °F); they are hardy but can be sensitive to prolonged cold-water exposure.
Spawning Behavior & Trigger
Breeding usually follows a significant temperature change, often in spring — a simulated seasonal warming after a cooler period. During spawning, males chase the gravid female and prompt her to release eggs by bumping and nudging her, with fertilisation occurring in open water.
Egg & Fry Care
Fantail eggs are adhesive and range from white to yellow-orange when healthy; a single female can produce a large number of eggs. Eggs attach to dense plants such as Cabomba or Elodea or to a spawning mop, and hatch within 48 to 72 hours. Fry begin assuming their final shape within a week but may take a year to develop mature colour, remaining metallic brown until then. Adults readily eat eggs and fry, so separation aids survival.
Common Challenges
Good-quality fancy specimens result from rigorous fry selection (culling) to maintain the twin-tail body type. Fantails may also develop telescope eyes from around six months of age, which influences sorting of offspring by type.
Lionhead Goldfish Breeding Guide
Overview
The lionhead is a fancy variety of the goldfish, Carassius auratus, and shares the same reproductive biology as all goldfish. It is an egg-scattering, oviparous spawner whose eggs are sticky and become attached to water plants or submerged objects. Females spawn several batches of eggs across the breeding season rather than a single clutch.
Sexing
Sexes are not reliably distinguishable outside the breeding period. As the season approaches, males develop breeding tubercles (white pinhead-sized spots, also called breeding stars) on the gill covers, head and sometimes the leading rays of the pectoral fins. Females in spawning condition become noticeably rounder as they fill with eggs.
Conditioning
Goldfish reach spawning condition only with adequate space and good nutrition. Cool water temperatures over winter are necessary for proper development of the ova, so a seasonal temperature cycle helps prepare breeders. Condition adults on a varied diet before the intended spawning period.
Breeding Setup
Provide a spawning medium for the adhesive eggs to attach to, such as dense fine-leaved plants like Cabomba or Elodea, or an artificial spawning mop. Because the eggs cannot be moved once laid, the breeding container should already hold the spawning medium before chasing begins.
Spawning Behavior & Trigger
Spawning usually follows a significant rise in temperature, typically in spring. With temperatures around 20-23 degrees C (68-73 degrees F) males begin chasing gravid females, persisting from dawn until early afternoon, bumping and nudging them to release eggs. The sticky eggs scatter onto the plants or mop and are fertilised by the pursuing males.
Egg & Fry Care
Remove the parents as soon as spawning is over, because goldfish readily eat their own adhesive eggs, which cannot be relocated. Eggs hatch in roughly 48 to 72 hours (about four days), and fry become free-swimming around 24 hours later, at which point feeding begins with newly hatched brine shrimp or a fine fry food. Within a week or so the fry start to assume their final shape, though they remain a metallic brown like wild ancestors and may take a year to develop mature coloration.
Common Challenges
Lionheads are a selectively bred variety, so fry must be graded and culled to maintain the dorsal-less back profile and the characteristic head growth (wen); only a fraction of any spawn shows the desired form. Some heavily modified fancy goldfish can no longer spawn naturally because of their altered body shape, and hand-stripping is sometimes used, although it can injure the fish if done incorrectly.
Pompom Goldfish Breeding Guide
Overview
The Pompom is a domesticated variety of Carassius auratus that develops bundles of loose fleshy outgrowths between the nostrils, called nasal bouquets, on each side of the head. This unusual feature exemplifies how selective breeding has produced anatomical modifications absent in wild ancestors. Like all goldfish it is an egg-scatterer.
Conditioning
Goldfish reach sexual maturity only with sufficient water volume and the right nutrition. Mature, healthy adults are conditioned before the breeding season. The optimum temperature for goldfish is between 20 and 22 °C (68 and 72 °F); temperatures under about 10 °C (50 °F) are dangerous to fancy varieties and temperatures over 30 °C (86 °F) can also cause harm.
Breeding Setup
Provide dense aquatic vegetation such as Cabomba or Elodea, or a spawning mop, because the eggs are adhesive and attach to this material. A separate spawning tank lets the adhesive eggs be protected, as adults may eat young they encounter.
Spawning Behavior & Trigger
Breeding usually happens after a significant temperature change, often in spring. Males chase gravid females and prompt them to release their eggs by bumping and nudging them. The female scatters adhesive eggs across the plants or spawning mop.
Egg & Fry Care
The eggs hatch within 48 to 72 hours. In their first weeks of life the fry grow quickly, an adaptation born of the high risk of being eaten by adult goldfish, other fish and insects. Within a week or so the fry begin to assume their final shape, although a year may pass before they develop mature goldfish color; until then they are a metallic brown like their wild ancestors.
Common Challenges
The fleshy nasal bouquets are a fragile selectively-bred feature easily damaged on decor during the chase of spawning. Some highly selectively bred goldfish can no longer breed naturally due to their altered shape, and heavy culling of fry is needed to keep only those that develop a matched, symmetrical pair of nasal bouquets.
Shubunkin Goldfish Breeding Guide
Overview
The shubunkin is a single-tailed, hardy variety of the goldfish, Carassius auratus, and follows standard goldfish reproduction. It is an egg-scattering, oviparous spawner whose sticky eggs attach to plants or submerged objects; females release several batches of eggs across the spawning season.
Sexing
Sexes cannot be told apart reliably outside the breeding period. As the season nears, males develop breeding tubercles, white pinhead-sized spots on the gill covers, head and sometimes the pectoral fins, while gravid females become rounder and deeper-bodied with eggs.
Conditioning
Adequate space and good nutrition are required for goldfish to reach spawning condition, and cool water during the winter months is necessary for proper development of the ova. As a robust, single-tailed variety often kept in ponds, shubunkins respond well to the natural seasonal temperature cycle that conditions breeders.
Breeding Setup
Set up the spawning medium before chasing begins, using dense fine-leaved plants such as Cabomba or Elodea or an artificial spawning mop for the adhesive eggs to attach to. The eggs cannot be moved after being laid, so the medium must already be in place.
Spawning Behavior & Trigger
Spawning usually follows a significant rise in temperature in spring. At around 20-23 degrees C (68-73 degrees F) males chase gravid females from dawn into early afternoon, bumping and nudging them so they release eggs, which scatter over the plants or mop and are fertilised by the pursuing males.
Egg & Fry Care
Remove the parents once spawning is over, because goldfish eat their own adhesive eggs and the eggs cannot be relocated. Eggs hatch in roughly 48 to 72 hours (about four days), and fry are free-swimming around 24 hours later, when feeding begins with newly hatched brine shrimp or a fine fry food. Fry take on their final shape within a week or so but remain metallic brown like wild ancestors, often needing about a year to develop adult coloration.
Common Challenges
The shubunkin is bred for its nacreous calico pattern of blue, red, orange, black and white, so fry are graded and culled to select the desired colours and pattern; only a portion of each spawn shows good calico. Being a single-tailed variety with an unmodified body, shubunkins spawn naturally without the difficulties of heavily modified fancy goldfish.
Telescope Goldfish (Carassius auratus) Breeding Guide
Overview
The Telescope is a fancy variety of the goldfish, Carassius auratus (family Cyprinidae), distinguished by significantly enlarged, projecting eyes. The trait was first developed in China in the early 1700s, where it was called 'dragon eyes'. The body resembles that of the ryukin and fantail, with a deep body and long flowing fins. Because the large eyes give the fish poor vision, it is best kept and bred with other slow, vision-impaired fancy goldfish.
Sexing
As in all Carassius auratus, mature males develop breeding tubercles — small white pimple-like bumps — on the gill covers and leading pectoral-fin rays during the breeding season; these fade after spawning. Females fill out, becoming plumper with eggs. Tubercles can occasionally appear on females, so body shape and tubercles are best assessed together.
Conditioning
Telescopes are hardy and tolerate a wide range of temperatures. A varied diet brings females into roe and prepares males. Because their vision is poor, food must be easy to find; this is the main husbandry difference from single-tail varieties during conditioning.
Spawning Behavior & Trigger
Breeding usually follows a significant temperature change, often in spring — a simulated seasonal warming after a cool period. During spawning, males chase the gravid female and prompt her to release eggs by bumping and nudging her, with fertilisation in open water.
Egg & Fry Care
Goldfish eggs are adhesive and attach to dense plants such as Cabomba or Elodea, or to a spawning mop, hatching within 48 to 72 hours. Fry begin assuming their final shape within a week but may take about a year to develop mature colour, staying metallic brown until then. Adults readily eat eggs and fry, so separation improves survival.
Common Challenges
Telescope eyes develop gradually in juveniles, and young black telescopes may change colour with age. Rigorous fry selection (culling) is used to keep the body and eye type; offspring are sorted as the telescope-eye trait emerges. Distinct colour forms include the all-black Black Moor, panda, calico and white.