Goldfish 101: Species Overview, Care & Breeding Guide

If you’re seeking a freshwater fish to beautify your aquarium and provide long-lasting companionship, common goldfish are an excellent choice.

It’s a rewarding and soothing hobby to raise this species. They are extremely easy to nurture and, thus, are delightful pet companions for beginners!

Sounds intriguing? Let’s know more about these popular fin-buddies.

Species Overview

Origin	Asia: China, North Korea, South Korea, Mongolia, Taiwan, Vietnam, Japan. Rivers: Amour, Kikuchi-gawa, Shira-gawa, Yuan Jiang
Order	Cypriniformes
Family	Cyprinidae
Scientific Name	Carassius auratus
Common Names	Prussian carp, native carp, common goldfish, golden carp, gold crucian carp, gibel carp, crucian carp
IUCN Red List Status	Least Concern
Appearance	Typically solid orange or bicolored. Can be red, yellow, and white. Elongated, flat body that tapers from back to belly with forked tail fin
Size (Adult)	On average, 15 cm (6 in) in captivity In the wild, 12-22 cm (4.7-8.7 in)
Lifespan	Up to 10-20 years
Temperament	Peaceful, Social, and non-territorial
Tank Level	All levels
Water Temperature	18-27 °C (65-80 °F)
pH Level	6-8
Water Hardness	5-25 dGH
Care Level	Easy
Minimum Tank Size	75 gallons for a pair, Min 55 gallons for a pair of juveniles
Tank Environment	Spacious tank with plants, caves, rocks, driftwood, and hiding spots
Diet	Omnivorous
Tank Mates	Other compatible goldfish species, easy-going, non-aggressive, similar-sized species with similar temperature preferences and activity levels

Natural Habitat

The common goldfish is native to Asia and can be found in countries like China, North Korea, South Korea, Mongolia, Taiwan, Vietnam, and Japan.

It inhabits calm, slow-moving waters such as lakes, ponds, and rivers, often swimming among plants and coexisting with other fish. The fish prefers cooler temperatures but can tolerate mild temperature variations.

It’s currently classified as Least Concern on the IUCN Red List, signifying a stable population with no major threats to their natural habitat.

Classification

The fish belongs to the Cyprinidae family under the Cypriniformes order.

Its scientific name is Carassius auratus. It goes by common names Prussian carp, native carp, common goldfish, golden carp, gold crucian carp and gibel carp.

Brief History

Goldfish have a rich history dating back to ancient China, where they were originally wild carp raised for food.

Over time, genetic mutations produced colorful variations that caught the attention of Buddhist monks, leading to the development of ornamental goldfish.

Selective breeding for fancy varieties began in the 1600s, and they became symbols of prosperity. They arrived in North America in the 1850s. Today, there are over 200 diverse goldfish varieties, including single-tailed and fan-tailed types.

Hybridization

Goldfish can crossbreed with certain Carassius carp species. Koi and common carp can also hybridize with goldfish, resulting in sterile hybrid offspring.

Appearance

If you want to know how these species look, let me take you through the details of their captivating beauty.

Size

The average size for wild goldfish is around 12-22 cm (4.7-8.7 in). In captivity, common goldfish grow up to 15 cm (6 in), but some individuals have grown much larger.

The world’s longest goldfish in captivity measured 47.4 cm (18.7 inches) from snout to tail-fin end and belonged to Joris GIjberg in The Netherlands.

The largest goldfish in the wild was named The Carrot, which weighed 67 pounds and was captured at Bluewater Lakes in France.

Color

Common goldfish typically exhibit solid orange or two-color combinations, often including black and orange.

It can also appear in shades of red, yellow, and white. The most notable and distinct variation is a bright orange metallic color.

Color Change

It’s important to know that goldfish changing colors is a common and natural occurrence, not a disease. Never attempt to treat it with antibiotics, as this can harm the fish.

Most color changes occur in the first year of their lives, but some goldfish continue to modify colors throughout their lives.

It’s worth noting that purebred goldfish typically show more color changes than ones with uncertain parentage, which may have a random mix of genes.

However, if you notice a goldfish’s skin and eyes becoming dull, it should be a cause for concern and requires attention, regardless of color changes.

Features

The common goldfish has an elongated, flat body. It has a short, wide head, and the body tapers smoothly from its back to its belly, culminating in a forked tail fin.

Fins are typically short and stand upright. The fish sports a dorsal fin with a slightly concave edge and a stripe running along its belly.

Teeth

Goldfish have small, flat teeth called pharyngeal teeth at the back of their mouth, used for grinding food.

Unlike human teeth, these teeth regenerate continuously and are located in the pharyngeal arch. You can see them by holding the fish still with its mouth open and appearing as small white bumps.

Sexual Dimorphism

Distinguishing between male and female goldfish can be challenging, especially outside of the breeding season.

Juvenile goldfish of both genders look very similar until they reach sexual maturity at around 12 months of age.

Male Goldfish

During the breeding season, male goldfish develop white pimple-like spots or breeding tubercles on their gill covers, head, and the leading edge of their pectoral fins.

Female Goldfish

Female goldfish may appear slightly fatter when they are carrying eggs. Their vent becomes enlarged and turns outward when they are ready to lay eggs.

Behavior & Temperament

The common goldfish is social and friendly. So, it often gets bullied by other boisterous and aggressive species.

Usually swims with conspecifics and shares food without harming each other but may turn aggressive during food competitions.

The species primarily swim in the middle and upper levels of the tank – unless during mealtime. They are often found exploring the bottom for food, also known as bottom feeders.

Vision and Hearing

The fish can sense ultraviolet and infrared light, which lets it spot prey and avoid predators. It can see clearly for about 15 feet and react to your presence.

It lacks ears but senses sound through vibrations and water movements. Excessive noise near its aquarium harms its hearing and causes stress.

Cognitive Abilities

The species possesses strong cognitive abilities, including associative and social learning skills.

It can distinguish between individual humans and show positive reactions like swimming to the front of the tank and begging for food from their owners. Fish with regular human contact become indifferent and can even be hand-fed.

Its memory spans at least three months and can even recognize time intervals. If you consistently feed and interact with them on a schedule, they will anticipate your actions.

It’s possible to train your goldfish to swim through hoops, respond to colored light signals, or dunk a miniature basketball.

Lifespan

With proper care, this fish can live for 10 to 20 years on average.

Tish, from the UK, lived for 43 years and holds the Guinness World Record for being the longest-lived goldfish.

Tips To Extend Your Pet Goldfish’s Longevity

To ensure your goldfish lives a long and healthy life:

• Provide a spacious tank that is wider than high for better oxygen exchange.
• Pre-set the tank through a ‘fish-less cycle’ for at least two weeks to establish essential bacteria.
• Create a stimulating environment with substrate and decor.
• Enhance oxygen levels with an air pump, air stone, or a waterfall filter.
• Maintain cleanliness with regular tank cleaning and filtration.
• Avoid removing the goldfish during water changes; use a gravel vacuum.
• Allow seasonal temperature variations, but stay within the range of 10-24°C.
• Feed it appropriately with goldfish-specific food and avoid overfeeding.
• It will live longer in an outdoor pond than in an aquarium.

Common Goldfish Care

If you’re eager to add this captivating fish to your aquarium, let’s dive into the details of how to properly care for it!

Tank Size

For a pair of fully-grown goldfish, ideally, 75 gallons is a must-have. You may start with at least a 30-gallon tank for one, but the species feel comfortable in groups, so it is advisable to at least keep two of them together.

If you have a pair of juveniles, consider 55 gallons minimum. As your goldfish grows, remember to upgrade their tank for more space. Adding 5 gallons per 1 inch of growth is suitable.

Keeping in a Fish Bowl

You’ve probably seen goldfish in a fish bowl in many cartoons. However, this is not suitable because the species is social, messy, large, and long-lived.

It should be kept in groups in spacious aquariums. In some countries, it’s even against the law to house them in bowls or alone. This practice can lead to water pollution and insufficient oxygen for their well-being.

Water Chemistry

This fish is quite adaptable to shifting water parameters. But you should provide them with the following water conditions to keep them happy and healthy:

• pH Levels: 6-8
• Water Temperature: 18-27 °C (65-80 °F)
• Water Hardness: 5-25 dGH
• Ammonia: 0 ppm
• Nitrite: 0 ppm
• Nitrate: Below 30 ppm (tolerance: less than 110 ppm)

Tank Environment

A well-designed aquarium environment with gravel, accessories, or plants is vital for your pet fish to stay engaged and for its good mood and health. Let’s craft the ideal habitat to ensure the best possible living conditions!

Substrate

The fish likes to pick up gravel with its mouth and spit it out. So, small gravel is not recommended as it can get stuck in its mouth.

Opt for larger materials like smooth river rocks after thorough rinsing. Sand is a good choice, being fine enough to not get stuck. Keep the substrate 1-2 inches thick.

Some prefer a bare-bottom setup for easy cleaning, but the substrate can support beneficial bacteria important for goldfish health. However, avoid using rocks from local waterways to prevent the spread of parasites and other diseases.

Plants

The fish nibbles and digs into the substrate to uproot plants. To avoid this, anchor your plants in the substrate and secure them with heavy stones.

Choose robust plant species that can withstand nibbling and damage. Selecting plants for goldfish tanks can also be challenging due to its preference for cold water and higher pH levels.

You can try keeping the following in your tank:

• Java moss
• Marimo moss ball
• African onion plant
• Water sprite
• Elodea
• Hornwort
• Pothos
• Anubias
• Amazon sword
• Cryptocoryne wendtii
• Duckweed
• Vallisneria
• Java fern
• Moneywort
• Java fern
• Dwarf anubias
• Crypts
• Eelgrass
• Tradescantia
• Bamboo

You can also keep fake plants, as they are easier to maintain. But live plants are still a better choice as they improve water quality by absorbing CO2 and releasing oxygen.

Lighting

Goldfish need daily light for healthy sleep patterns but avoid direct sunlight. Tank lights are fine indoors, but give it a “lights out” period to mimic its natural sleep-wake cycles.

You can use LED aquarium lights as they don’t produce excess heat. Limit lighting to 8-12 hours and reduce it even further if there is a lot of algae growth.

Décor

Choose non-hollow, non-sharp decorations like rocks, caves, and driftwood. Create hiding spots and leave open areas for swimming. Don’t use corals and plastics, as they can upset your goldfish tank’s balance.

Filtration

Goldfish need a filter in their tank or pond because it produces a lot of waste. External filters are better as they can clean more water effectively.

When choosing a filter, focus on the flow rate, which should be at least 5 times your tank’s volume per hour, ideally closer to 10 times. For example, a 20-gallon tank should have a filter with a flow rate of 100 to 200 gallons per hour.

Water Flow Rate

Maintain a gentle water current in your fish tank, replicating its natural habitat in slow-moving rivers. Avoid powerful currents that can stress your goldfish.

Use options like air stones and sponge filters to provide a gentle, adjustable current, promoting their well-being and tank hygiene.

Food & Diet

The common goldfish is omnivorous, enjoying a diet of plant material, small insects, and crustaceans in the wild.

In a tank, aim for a balanced diet with around 40% protein, 44% carbohydrates, 10% fats, and 6% minerals. Consider choosing food with a healthy dose of Omega 3s to enhance your fish’s color.

A well-balanced goldfish diet includes flakes, sinking pellets, floating pellets, live foods, freeze-dried live food, and vegetables.

You can feed them with the following:

• Daphnia
• Krill
• Romaine lettuce
• Oranges
• Bloodworm
• Feeder shrimp
• Duckweed
• Brine shrimp
• Spinach
• Kale
• Cucumber
• Peas
• Daphnia eggs
• Mosquito larvae
• Sinking algae disk

For adult goldfish, it’s best to feed them once every 24 hours, preferably right after their tank lights switch on. This is because they naturally start looking for food at dawn and dusk. Consistency in feeding times helps them anticipate meals and become more active.

Fasting them one day a week would keep them healthy. They will graze on algae and hunt for food scraps during the fasting day.

These fish are always hungry and will try to eat anything in their surroundings, even gravel or plants. Be cautious not to overfeed, as it can lead to major health problems and increased waste production.

Feed them small portions that they can finish in 1 to 2 minutes. Avoid overcrowding the tank to prevent food competition and stress.

Prior to feeding, defrost frozen foods if applicable. Keep them on a sinking diet to minimize excess air consumption while eating. While pelleted food is a good option for its longer-lasting quality, if using flakes, consider presoaking to prevent buoyancy issues.

These species can tolerate hunger for 8 to 14 days, scavenging their environment for algae and small insects. In ponds, with access to algae and insects, they can go without food indefinitely.

Tank Mates

The common goldfish needs its own group. Make sure that you have 1-2 other common goldfish or other compatible goldfish breeds to make it feel at ease.

For other tank mates, remember it is calm and peaceful. So, its tank mates must be easy-going, non-aggressive, similar-sized species with similar temperature preferences and activity levels. Some compatible tank mates are listed as follows:

• Dwarf gouramis
• Kuhli loaches
• Hillstream loaches
• Neon tetras
• Hog Nosed catfish
• Dojo loaches
• White cloud mountain minnows
• Hoplo catfish
• Variable platies
• Longfin rosy barbs
• Rosy barbs
• Giant danios
• Rubber lip plecos
• Zebra danios
• Japanese rice fish
• Bristlenose catfish
• Banded corydoras
• Bristlenose plecos
• Albino corydoras
• Rosy barbs
• Harlequin rasboras
• Pangasius catfish
• Black mollies
• Guppies

They also do well with invertebrates like:

• Mystery snails
• Apple snails
• Nerite snails

Tank Mates to Avoid

Other than that, here are some fish that you must avoid housing in the same tank:

Aggressive fish (e.g.: barbs, African cichlids, and other large cichlids): They may harass and stress out your peaceful goldfish. Goldfish are not equipped to defend themselves against aggression.

Small and spiny fish (e.g.: otocinclus): Goldfish may swallow smaller tank mates and the spiny fish may get stuck in its gill plate.

Territorial fish: Goldfish swim at all levels and don’t respect territorial boundaries. They may face undue stress and conflicts with territorial species.

Tropical fish (e.g.: betta fish, discus fish, or warm-water tetras): They require warmer water temperatures, unlike the coldwater goldfish.

Freshwater shrimp (e.g.: cherry shrimp and bamboo shrimp): Goldfish may view freshwater shrimps as food.

Incompatible goldfish varieties: Different goldfish varieties have varying swimming abilities and energy levels. Avoid mixing incompatible varieties, as this can lead to stress.

Fish with different diet requirements: Tank mates that do not share a similar diet to goldfish can lead to overfeeding and potential health issues for the goldfish.

Common Diseases

Goldfish are resilient and can withstand many diseases due to common mistakes made by beginners. But keep an open eye for the following to ensure their health and survival:

Disease Name	Causes	Symptoms	Treatment
Dropsy (Ascites)	Kidney failure due to poor water quality and stress	Swollen belly, pinecone-like appearance	Isolate fish, medicated food, antibiotics, and Epsom salt
Neurofibroma (Tumor)	Genetic, overexpression, and replication of cells	Skin and fin lumps	Surgical removal or medication (less effective)
Fluke	Parasitic infection from poor diet or water quality	Scratching, rapid breathing, mucus, red skin, sunken belly	Disconnect biological filters, Droncit, and water treatment
Anchor Worm	Parasitic infestation, often introduced by new fish	Worm-like parasites near fins	Remove with tweezers, salt bath, and Diptera solution
Fish Lice	Crustacean infestation from new fish or objects.	Fish rubbing against objects, missing scales, injured fins	Sterilize tank, remove lice, salt bath, and Diptera solution
Ulcers	Bacterial infection from injury, often with parasites	Pink/red open sores on the skin	Hydrogen peroxide, salt bath, and antibacterial medication
Fin Rot	Bacterial infection due to poor water quality or cold temperatures	Damaged fins and bacterial growth	Salt bath, trim damaged fin, and antibiotics if severe
Fungus	Fungal infections in stressed or injured fish	White cotton-like patches on the body or fins	Salt baths, treat other diseases first and improve water quality
Carp Pox	Infectious diseases often introduced by new fish	Thickening of fins and candle wax lesions	Strengthen the immune system and maintain water quality
Cloudy Eye	Various causes, including internal parasites and poor water quality	Thin white film covering the eye	Treat underlying issues and maintain water quality
Goldfish Turning White	Genetics, water quality, illness, low oxygen, lack of UV light, diet, genetics, aging	Symmetrical color shift, irregular white patches, illness signs, lethargy, pale colors with aging	Monitor water quality, quarantine, consult vet, adjust conditions, provide UV light, improve diet, no treatment for genetics and aging
Goldfish Turning Black	Genetics, camouflage, ammonia burns, stress, overfeeding, light exposure, black spot disease	Gradual or sudden darkening, red marks, behavioral changes, and stress stripes	Maintain water quality, provide proper lighting, avoid aggressive tank mates, quarantine new fish, avoid overfeeding, add live plants, and consider a bigger tank

Breeding & Reproduction

Breeding common goldfish can be a rewarding endeavor, but it’s essential to understand that it comes with challenges and responsibilities.

It demands dedication, space, and resources. You will need significant investment in tanks, equipment, and care. Breeding often involves culling of fry, which can be emotionally challenging.

Preplanning

Goldfish typically breed at one to two years old, so raise them for at least a year before breeding. Watch for health issues and genetic traits as they mature to select the best breeders.

Identify potential parents by July or August the year before, as goldfish breed in spring. Keep records of their health and issues for better stock selection. Some breeders suggest treating them for parasites before breeding.

In my experience, it’s better to introduce 2 or 3 male and 1 female goldfish for successful mating.

Ensure Fish Health

Choose healthy goldfish with good morphology and no history of health issues, such as swim bladder disorder or tumors. Ensure they are disease-free.

Some breeders prefer to separate males and females for a few weeks before breeding.

Prepare a Breeding Tank

Invest in a breeding tank of at least 90 gallons in size, equipped with a gravel bottom.

Maintain a lush environment in the breeding tank with solid surfaces for the spawning process and for the eggs to adhere to.

Bushy, oxygenating plants like Anacharis work well. But artificial plants or fibrous spawning mops can also be used.

Condition the Breeding Fish

Feed the fish with high-protein foods, like brine shrimp, worms, and high-quality pellets, during this period to prepare them for spawning. Follow a diet of three to four feedings daily with small portions during conditioning.

When breeding, provide as much food as they can consume in a few minutes. It should be just enough to avoid leftover food to maintain water quality in their breeding tank.

Water Parameters to Mimic Seasonal Change

Goldfish breed in spring, but you can use a chiller to control the temperature and simulate winter. Slowly lower the aquarium temperature to 10-12°C (50–54°F), decreasing the chiller by 1-2°C (1.6–3°F) daily.

The fish will naturally stop eating and enter a near-hibernation state called torpor as temperatures drop.

When they are ready to breed, mimic spring by gradually raising the aquarium temperature by 1–2°C (1.6–3°F) daily until it reaches 20–23°C (68–74°F). This takes approximately a week.

Signs of Pregnancy

The male goldfish may develop small white bumps called spawning tubercles near their gills and pectoral fins, signaling readiness to mate. He chases the female by nudging under her tail or belly as part of the mating ritual.

While this is normal, persistent chasing can stress the female. Only in this case, you must maintain a higher female-to-male ratio.

In the female fish, the main sign of pregnancy is its visibly swollen belly. Sometimes, it grows up to three times its size, indicating that it’s ready to spawn. It may struggle to swim normally and might also exhibit changes in appetite.

Spawning

Spawning involves females laying eggs, which males fertilize. Eggs adhere to plants or a spawning mop. Spawning lasts two to three hours, producing from 100 to 10,000 eggs.

After spawning, promptly remove the parents to prevent them from consuming the eggs.

Dealing with Infertile Eggs

Fertile eggs are pearl-colored with black dots and should not be tampered with. Fertilized eggs have sticky threads that attach them to surfaces.

Infertile eggs turn white and develop a fungal coating.

Many experts suggest removing them. But these eggs are sticky, and even if you remove the infertile eggs, the sticky matter may have enough fungus to affect the fertile eggs.

So, instead, add methylene blue solution to the eggs to prevent the infection from spreading.

Egg Hatching

The eggs hatch within a week, depending on the temperature, producing dark-colored fry measuring half an inch long. The dark coloration helps protect them from predators.

Care for Fry

Avoid feeding fry right after hatching; they only need food once they start swimming. Until then, they can live on their egg yolk.

When they become free swimmers, feed them a mixture of hard-boiled egg yolk and water or small bits of live food like crushed brine shrimp.

It takes about three weeks for the fry to mature. Transfer them to a community aquarium once they reach over an inch in length. Ensure fry are strong swimmers, too big for the filter, and larger than the mouths of adult fish before adding them to the main tank.

Quick Buying Tips

When purchasing fish, carefully select a reputable seller. Check that the store aquariums for goldfish are not overcrowded, as overcrowding can stress the fish and also lead to illness.

Healthy goldfish exhibit clear and vibrant colors, are active, have erect fins, and swim smoothly.

Here are some signs that show a fish might not be healthy:

• Prolonged isolation in one corner of the tank.
• Slow and lazy behavior.
• Bouncing around strangely at the tank’s bottom.
• Presence of lumps or wounds on their bodies.
• Alone in one corner for a long time.
• Looks pale or not colorful.

A word from FIA

Did you find this article enjoyable and informative? We hope so!

Remember, common goldfish are easy and fun to care for – so long you have the right knowledge about their desirable habitat.

The low-maintenance goldfish is also pretty inexpensive compared to the fancier alternative. So, if you have the right setup, you can easily invest in a few. The sociable species also have distinctive personalities that can capture your heart!

If you found this information useful and think others might, too, please consider sharing the article with your friends and fellow fish enthusiasts. If you have any queries, shoot us an email, and we will reply to you right away.