General Information
The Goldfish (Carassius auratus) is a freshwater fish that thrives in cold water and originates in China. The goldfish in its current form was first bred more than one thousand years ago. Today we have many distinct breeds that differ in size, body and fin shapes, and color.
Goldfish Lifespan
The lifespan for a Goldfish is around 10 - 15 years if cared for accordingly.
There is a huge variance in goldfish lifespan, though. Most fancy goldfish breeds struggle to reach 5 years of age in a tank while the world's longest-lived goldfish even lived to be 43 years old. Goldfish also generally live longer (up to 25 years) when kept in ponds.
If you keep your goldfish in an aquarium tank, their lifespan will mainly depend on the specific breed, the water quality, size of the aquarium tank and quality food. Don't keep your goldfish in small tanks or fish bowls as this will affect their lifespan negatively.
If you're looking for longevity in your goldfish, look for breeds with a streamlined body shape (e.g., Common goldfish, Comet, Shubunkin) and avoid fancy breeds (e.g. Fantail, Ryukin, Telescope, Ranchu, Lionhead goldfish).
Please keep in mind that caring for an animal for such a long time is a big commitment and consider if you really want and can do that.
Appearance
Goldfish Size
The size of a goldfish depends on the breed and where and how it is kept. Goldfish that are kept in aquariums generally grow to between 2 inches (5 cm) to 6 inches (15 cm), depending on the tank size. When kept outdoors in a pond and in the wild they can grow to 14 inches / 36cm.
The final size of an adult Goldfish also depends on the genetic and the type and amount of available food sources. The more food is available, the more the animal will max out on its potential growth.
Make sure to provide adequate food for your Goldfish, but don't over- or underfeed as this brings its own problems. You can find more information on feeding below.
Goldfish Colors
Goldfish come in many different colors such as white, yellow, orange, red, brown, black and variations thereof.
Goldfish Shape
Goldfish can have different body shapes depending on the breed: streamlined, egg-shaped.
Goldfish breeds with streamlined bodies have a slender and prolonged body. They have a single tail, a dorsal fin, normal eyes and no wen. They are fast swimmers and more robust than the egg-shaped breeds.
Egg-shaped goldfish breeds are also called "fancy" breeds. Their bodies are more compact and shaped like an egg. They have twin tails and sometimes lack a dorsal fin. Some breeds have a wen, while others can have bulging eyes. They are slow swimmers and more fragile than streamlined breeds.
Water and Tank Requirements
Goldfish Water Temperature
Goldfish are cold water fish, which means they can live in outdoor ponds and unheated indoor aquariums. Rapid changes in water temperatures should be avoided because the stress might kill them. Temperatures between 68 °F (20 °C) and 73 °F (23 °C) are optimal.
Goldfish Water Parameters
Goldfish don't require a heater in their tank as their cold water fish and also survive outdoors when kept in ponds.
Goldfish Tank Size
Every Goldfish should have at least 10 gal (38 l) of water to themselves. So, if you want to keep 5 small Goldfish, there should be at least 50 gal (190 l) in your tank.
Please keep in mind that your aquarium hardscape also takes away from the overall water volume in your aquarium and that if you plan to add other fish to the tank you need even more water!
The calculated water amounts shouldn't be shared between species but always added up.
Goldfish Tank Requirements
In popular culture Goldfish are often shown as being kept alone in a fishbowl. Please don't do this as fishbowls are way too small for them and they don't like to be kept alone.
Behavior and Tank Mates
Goldfish are friendly towards their own and other species. This means they can be housed with other types of fish that are also generally friendly and have similar water and tank requirements.
Please note that even the most peaceful species can get aggressive when they feel threatened, e.g., when there is too little space in the tank or they have to fight with others for a limited food supply. Please always make sure to meet the requirements of your animals as closely as possible to avoid such issues.
They should be kept in groups of at least 2 animals. If kept in a smaller group they might get anxious and lethargic.
Keep in mind that goldfish are omnivores and will most likely eat anything that is smaller than them. Depending on the size of your goldfish that could be small shrimp and very small fish or their babies.
Goldfish are a foraging species, which means they will be digging through soil, gravel or sand looking for food. Be aware that this might mess up your aquascape and displace your soil layers and uproot plants. Goldfish are therefore more suitable for natural scapes and probably shouldn't be placed in tanks that are supposed to look perfect.
Fish generally don't sleep the same way mammals do and how exactly they sleep is still a topic of research. It is clear though, that they also have periods of rest where they move less and their metabolism is reduced.
Feeding
Goldfish are omnivores, eat all the time and won’t stop by themselves, so you need to make sure not to overfeed them. It’s best to buy specialized goldfish food and stick to the feeding recommendations on the packaging. Apart from that they will eat anything from insects, crustaceans, plants to vegetables and worms.
Breeding
Goldfish need enough clean water and nutrition to reproduce. Reproductive activity is usually triggered by a drastic temperature change, e.g., when the water turns warmer in spring. The male fish will develop little bumps on their cheeks and start bumping female goldfish that carry eggs to make them release the eggs. Those eggs will then be fertilized by the males and attach to plants. Goldfish develop quickly during the first weeks but it takes up to a year for them to develop their final color. Until then they appear metallic brown / black.
Common Problems
- overeating: They eat a lot though and can seem a bit aggressive when it comes to feeding, snatching all the food away before other species can get to it. Make sure to socialize them only with other species that can keep up or they might starve. They might also eat shrimp or baby fish. Overfeeding is also a problem when it comes to water parameters because more food leads to more waste, which results in higher nitrate levels. This can in turn become toxic for your animals.
- destroying plants: If kept in a planted aquarium, your goldfish might start ripping on plants inside the tank to eat them. You will have to trial and error which plants you can successfully keep in a planted tank with goldfish. In our experience the ate Blyxa Japonica, Pogostemon Helferi, Marimo balls, Amazon Frogbit, Monosolenium tenerum and Brazilien Micro Sword but left Dwarf Anubias, Cryptocoryne, Java Fern and Vallisneria alone.
- fin damage: Goldfish can have very long and delicate fins. Depending on the design of your tank and your hardscape, those fins might rip on sharp objects and get damaged. Fin damage can also be caused by a bacterial infection, so always make sure to keep your water clean and well-filtered. Specialized veterinarians will be able to correctly diagnose infections and recommend the right treatment.
- oxygen levels: Bigger goldfish usually need more oxygen in the water than the plants in the aquarium can provide. Therefore, it's advisable to put an air stone in the tank to make sure your fish have enough oxygen, especially if your fish seem to be grasping for air at the surface.
Fun Facts
- memory span: Goldfish having short memory spans of just a few seconds is a myth. They recognize their owners, anticipate feedings if they occur around the same time every day and can even learn tricks. They get very friendly towards their humans with time so they can even be hand fed and touched, although touching them should be avoided as it can potentially damage their skin's slime coat.