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Goldfish: Interesting and Surprising Facts About a Popular Pet

Linda Crampton is a writer and experienced science teacher with an honors degree in biology. She enjoys writing about science and nature.

A veiltail goldfish

A veiltail goldfish

Beautiful and Interesting Animals

Goldfish are common pets that have some surprising features. The colourful fish are found in many home aquariums, especially those designed for children. They are believed to be descended from carp. They are often thought of as attractive but relatively simple (and simple-minded) creatures. Scientists and enthusiasts have made some interesting discoveries which show that there is more to the animals than is sometimes realized.

I had both indoor and outdoor goldfish as pets in my childhood and early teens. I enjoyed watching the fish and exploring their behaviour. Goldfish can make good pets. Unfortunately, they are sometimes kept under conditions that are far from ideal. As is the case for other animals kept in captivity, their living conditions are important to consider.

According to the Bristol Aquarists' Society in the UK, the Prussian carp, or Carassius gibelio, was probably the ancestor of the goldfish.

A Brief History of Goldfish

The goldfish has the scientific name Carassius auratus. It's a member of the family Cyprinidae, which includes carp. The colour of the fish is believed to have first appeared—or at least to have first been noticed—in carp living in Ancient China.

The carp were raised in ornamental ponds or as food fish. A few of the normally silver fish had a mutation (gene alteration) that gave them a beautiful orange-yellow or golden colour. These fish were selectively bred to produce more coloured offspring as well as animals with fancy tails and other unusual features. The new varieties of carp were greatly admired. They eventually became known as goldfish.

A common myth says that goldfish can remember things for only three seconds, but this is grossly inaccurate. They have been found to remember some things that they've learned for over a month. (Yes, goldfish can learn.)

Memory and Learning

Researchers at Plymouth University trained goldfish to press a lever to get food. Once the fish had learned to do this, the researchers changed the conditions of the experiment so that the lever released food only during a specific hour in each day. The goldfish recognized and remembered the time of day when pressing the lever was fruitful. They gathered around the lever during the correct time and pressed it to obtain food but ignored the lever at other times.

Jamie Hyneman from the MythBusters TV show also tested goldfish memory. He trained his fish to swim through an underwater maze consisting of multiple barriers. Each barrier had a hole surrounded by a red ring. The ring in a barrier was located at a different level from the one in the previous barrier. The goldfish remembered that they needed to travel through the holes to find food and reached the food faster over time. The experiment was continued for forty-five days.

Adam Savage from MythBusters also tested goldfish memory, but his fish weren't successful in navigating the maze. Adam's attempt shows how variables may affect the result of an experiment. He put different materials into the water from Jamie, which may have affected it chemically. In addition, he had a smelly waste problem in his tank and used green rings in the maze instead of red ones. All of the fish except for two died.

The surviving fish in Adam's experiment may have failed the maze test for one or more reasons. They may have been harmed by the chemical or waste problem; they may have been unable to see green rings as well as red ones; and they may have had less chance to copy a successful fish's behaviour, since only two animals survived.

Researchers Teach Goldfish to "Drive"

Israeli researchers from Ben Gurion University of the Negev have recently announced the results of an interesting experiment related to goldfish intelligence. They taught goldfish to move a robotic cart on wheels. The cart was attached to a camera. The camera recorded the direction in which the fish was pointed as it swam and triggered the cart to move in that direction. The fish moved the tank to strike a coloured goal, which resulted in the animal receiving a treat.

The goldish needed to be trained in order to perform the task, and some fish were better learners than others. Still, the fact that the animals could learn how to perform the task is impressive. The experimental setup is shown in the video below. As shown in the beginning of the video, the scientists allowed at least one fish to explore beyond the laboratory.

Surprisingly, it doesn't take the fish a long time to learn how to drive the vehicle. They're confused at first. They don't know what's going on but they're very quick to realize that there is a correlation between their movement and the movement of the machine that they're in.

— Shachar Givon, Ben Gurion University of the Negev, via CNN

Surviving Under Ice

Researchers at the Universities of Liverpool and Oslo have made an interesting discovery about a goldfish relative named the crucian carp (Carassius carassius). They've found that a major reason why the fish can survive under the frozen surface of a pond in winter is because of the alcohol that its body produces.

Like other fish and many other aquatic organisms, crucian carp and goldfish breathe by extracting oxygen from the water that flows through their gills. Under a layer of ice, the oxygen soon disappears. Most vertebrates die if they are covered by ice and have no way to escape.

Vertebrates such as fish and humans need oxygen so that their cells can produce energy via the appropriate chemical reactions. A small amount of energy can be produced without oxygen. Unfortunately, during this reaction lactic acid is produced. This substance quickly builds up to a dangerous concentration when no oxygen is available.

Members of the genus Carassius appear to solve this chemical problem by converting the lactic acid to alcohol, which enables them to survive. The researchers have discovered that their blood alcohol level becomes higher than the legal limit for driving in some countries. Apparently the alcohol is less damaging than the lactic acid because the fish can survive under the ice without oxygen for months. They remain conscious but aren't very active. The scientists say that their discoveries apply to both the crucian carp and goldfish.


Caution is needed when analyzing the results of the experiment described above. According to the scientific report referenced below, most of the research seems to have been done with the crucian carp and only a little with the goldfish. Pet goldfish should be provided with a good supply of oxygen.

Giant Goldfish in the Wild

The existence of giant goldfish is not a myth. Assuming the animal eats enough food, the size of a goldfish is determined in large part by the size of its container, although genetics plays a role as well. If the fish are released into a large pond or a river, either deliberately or due to the flooding of an outdoor pond in a garden, they will likely become very big. That's exactly what's happening in some parts of North America and Europe, in Australia, and perhaps in other parts of the world. The fish are living and reproducing in the wild in areas as far north as the province of Alberta in Canada, which has cold winters.

The goldfish also lives and breeds in the wild in the United States. The USGS (United States Geological Survey) recognizes the animal as a non-indigenous aquatic species. The organization says that although orange individuals are occasionally found, the population of wild goldfish in the United States has mostly reverted to a pale olive-green colour.

The problem with releasing animals into an area where they don't belong is that they may harm the ecosystem. A mature ecosystem normally develops some kind of balance that enables many species to survive. An introduced animal may alter this balance. For example, studies have found that introduced goldfish compete for food needed by other species. The fish are also expanding their diet. In one area they eat salamander eggs "with fervour".

Pet Fish

Goldfish are found in every pet store that I visit and are often inexpensive to buy. This seems to have led to some disrespect for the fish, which I find sad. I remember seeing goldfish in plastic bags being given as prizes at fairs when I was a child. Unfortunately, they still are in some places. Goldfish won't live long if they're treated casually and aren't well cared for.

There are many things for a prospective goldfish owner to consider. These include:

  • tank size
  • a suitable location for the tank
  • gravel type
  • items to put in the tank
  • suitable food for the fish
  • a suitable water filter to remove waste materials
  • aeration (A water filter with a pump will probably provide enough aeration as it operates.)
  • water temperature
  • a method of water conditioning (Chlorine must be removed from water before fish come into contact with it.)
  • a method for cleaning the aquarium
  • a way to safely replace water lost due to evaporation
  • a method for gradually changing the water (Replacing the evaporated water is not the same as changing the water.)

Someone who wants to keep goldfish as pets should investigate all of the requirements needed to keep them healthy and happy. A person should also identify a veterinarian who can provide help for any serious health problems that develop in the fish. These vets do exist.

Size and Lifespan of Pet Goldfish

Some people may be amazed to discover how big pet goldfish can get and how long they can live in a large tank and with proper care. In a small tank, goldfish may reach a maximum length of only around five inches and live for only a few years (or less). In a big tank, they may reach as much as ten to twelve inches in length —or even longer—and live for as long as twenty-five years. A few have lived into their thirties and early forties. These statistics are especially likely for the plainer varieties of goldfish, which seem to be hardier than the fancier kinds.

Bubble eye goldfish (shown in the video above) have no dorsal fin and are poor swimmers. They spend most of their time on the bottom of the tank. They are fragile animals that are known for getting sucked into the intake area of water filters. If the fluid filled "bubbles" by the eyes burst, the animal may develop a serious infection.

Selective Breeding of the Animals

Several hundred different varieties of goldfish exist. They vary in colour, pattern, body shape, and features. Some varieties no longer look like goldfish. Some look like they have been inflated and/or have protuberances from various parts of their body. These protuberances may interfere with vision, swimming, or even breathing.

Selective breeding of domesticated animals can produce interesting and useful results. Some of the unusual characteristics of the fancy goldfish varieties are attractive and don't interfere with the lives of the fish. I think it's very wrong if breeding is done with the knowledge that it will probably make life difficult for the offspring, though.

In my opinion, fish shouldn't be bred simply to satisfy people's desire to have bizarre animals in their collection, especially when there is no concern about an animal's quality of life. It would be far better for people to buy plainer and less expensive varieties of goldfish—which I think are beautiful and interesting—and spend any money that's left over on a large tank and other items needed to keep the fish healthy and reasonably happy.


  • "Background Information About Goldfish" from the Bristol Aquarists' Society
  • "Do fish really have a 3 second memory?" from The Naked Scientists (a group based at the University of Cambridge)
  • A different article entitled "Do Fish Really Have a Three-Second Memory?" from Mental Floss
  • Scientists teach goldfish to "drive" from CNN
  • Some members of the genus Carassius go months without oxygen by making alcohol inside cells from New Scientist
  • Extreme hypoxia tolerance in crucian carp and goldfish from Nature Scientific Reports
  • Facts about Carassius auratus from the United States Geological Survey

© 2017 Linda Crampton


Linda Crampton (author) from British Columbia, Canada on April 23, 2020:

I agree that all sentient beings should be treated well. Fish have some features that are more advanced than many people realize.

Peggy Woods from Houston, Texas on April 23, 2020:

I think that all sentient beings, whether animals or fish, should be cared for properly. My aunt and uncle, who used to live in Milwaukee, Wisconsin, had an outdoor pond in which goldfish were kept. It amazed me that they could survive the winter months with the frozen pond. Now, thanks to you, I know why.

Linda Crampton (author) from British Columbia, Canada on October 20, 2019:

Thanks for sharing the story, Louise. I think that goldfish have more abilities than many people realize. Thank you for caring for the two that you had.

Louise Elcross from Preston on October 20, 2019:

I rescued a goldfish from the fairground and it was in a plastic bag. I took it home not expecting it to survive but it did. I had the fish for many many years. When the fairground came again they had more fish in plastic bags so I brought a tiny one home. Both fish lived for many years with the second fish outliving the first fish by about 9 years. They used to get excited as I approached their tank because they knew it was feed time. It broke my heart when I went to feed the fish one morning and he had died. They were both lovely.

Linda Crampton (author) from British Columbia, Canada on July 05, 2018:

Hi, Nathan. Yes, goldfish have some surprising abilities. They are interesting animals.

Nathan M from Tucson on July 05, 2018:

Interesting that goldfish have somewhat better memories that we had expected them to. I also always wondered how some fish managed to live under the ice surface in a lake. Goldfish seem to have developed a rather interesting to do so.

Linda Crampton (author) from British Columbia, Canada on January 17, 2018:

Hi, Bede. Goldfish are certainly enjoyable to observe. It would be interesting to perceive the world as they do for a while, as long as I could be sure that I would become a human again! Thanks for the interesting comment.

Bede from Minnesota on January 17, 2018:

Quite fascinating! Wouldn’t it be interesting to be a goldfish for a day? I’d probably go easy on the caviar, though. It’s quite impressive that they can work their way through a maze, especially if under the influence. I agree with you about creating bizarre fish for recreation with no concern for their welfare.

Linda Crampton (author) from British Columbia, Canada on December 01, 2017:

Thank you very much for the comment, Catherine!

Catherine Giordano from Orlando Florida on December 01, 2017:

What a treasure trove of information about goldfish, all of it fascinating and most of it unknown to me. I love learning new things. Thanks for educating me.

Linda Crampton (author) from British Columbia, Canada on November 23, 2017:

Thanks for the comment, Alex. Goldfish are surprising animals!

Alex Anghel from Romania on November 23, 2017:

Had no idea that this little fish is so amazing. Who knew they are so intelligent creatures? Thank you for the info!

Linda Crampton (author) from British Columbia, Canada on November 20, 2017:

Hi, Colin. A long time ago I had goldfish in an outdoor pond, too. The fish are a lovely part of a garden. It sounds like you're taking care of yours very well.

colin powell from march on November 20, 2017:

That was interesting. I was of the three-second memory school. I never realised they could learn and retain information for such periods of time. I have goldfish in my garden pond. We had to make sure of filters, waterfall and oxygenating plants. When we first got them, they were rather small but have grown in a short time.

Linda Crampton (author) from British Columbia, Canada on October 25, 2017:

I'm glad that Louise and the other residents enjoy watching the fish, Peg. They can be interesting animals.

Peg Cole from North Dallas, Texas on October 25, 2017:

Who knew that goldfish could figure out things like going through a maze? Wow, that's incredible. There's a fish tank at the nursing home and Louise loves to watch the fish swim. Even at 97, she has her favorites. It seems to have a calming effect and watching the fish swim is relaxing for the residents.

Linda Crampton (author) from British Columbia, Canada on October 21, 2017:

Thanks for sharing the interesting information, Nancy. I'm glad the goldfish survived after his or her adventure!

Nancy Owens from USA on October 21, 2017:

I love the photos in this article! When I still had livestock, I kept goldfish in the water troughs to keep them clean. It was easy because the fish fed on the remnants of hay and grass that got left behind after horses and cows drank, and also kept the algae growth down. In working with irrigation pumps, we once had to take a pump apart because a very large goldfish had gotten sucked up through a foot valve all the way up to the impeller of the pump. He or she was still alive, with only a small abrasion on its back, so I carried it down to the pond and it swam away. We replaced the broken screen so it wouldn't happen again.

Linda Crampton (author) from British Columbia, Canada on September 07, 2017:

Thank you, Catherine. I've researched the intelligence of bees, too. Many animals seem to have more advanced mental abilities than we previously realized. It's a shame that we underestimate them.

Catherine Giordano from Orlando Florida on September 07, 2017:

This is a fascinating article and very well written. I had no idea that goldfish were so smart. I did research on the intelligence of bees and they have amazing mental capabilities also. I think we so often underestimate the intelligence of animals.

Linda Crampton (author) from British Columbia, Canada on September 03, 2017:

Thank you for the interesting comment, Martie. It can certainly be interesting to watch goldfish swimming. I didn't realize that the fish were once so popular in South Africa.

Martie Coetser from South Africa on September 03, 2017:

At a time - during the 60s and 70s, before TV came to SA - every household had a fish tank. Families would spent their evenings, chatting while watching the movements of the fish in the tank.

Thanks for this informative hub about Goldfish, Alicia!

Linda Crampton (author) from British Columbia, Canada on August 24, 2017:

Hi, Bill. Goldfish have some interesting features. I enjoy observing and studying the animals.

Bill De Giulio from Massachusetts on August 24, 2017:

How interesting Linda. I always wondered how they survived winters under the ice. Thanks for the education. I had no idea the Goldfish was trainable and could get so large.

Linda Crampton (author) from British Columbia, Canada on August 19, 2017:

Hi, Peggy. Thanks for the visit. Goldfish do have some surprising abilities!

Peggy Woods on August 19, 2017:

What interesting information you have provided about goldfish. I often wondered how they could survive under a layer of ice in ponds. Now thanks to you I know the answer.

Linda Crampton (author) from British Columbia, Canada on August 18, 2017:

Thank you for the very interesting comment, moonlake.

moonlake from America on August 18, 2017:

We use to have a pond with goldfish in it. Here it can get 30-40 below but when our pond opened in the spring the fish were swimming around. People said here long ago they use to put goldfish in the cow or horse tough to keep the water from freezing.

You hub was very interesting I enjoyed it.

Linda Crampton (author) from British Columbia, Canada on August 18, 2017:

Thank you very much, Dora.

Dora Weithers from The Caribbean on August 18, 2017:

Informative and interesting about the gold fish, especially about their memory. Thanks for the very well-presented lesson.

Linda Crampton (author) from British Columbia, Canada on August 18, 2017:

Hi, nicey. The colours of goldfish are certainly beautiful. I hope your fish do well.

nicey on August 18, 2017:

Hello,I enjoyed your article. I quickly noted in my to do list to start breeding fishes at home . I don't like catfish but small colored fishes are a beauty to behold.


Linda Crampton (author) from British Columbia, Canada on August 17, 2017:

Thanks, Larry. I appreciate your visit.

Larry Rankin from Oklahoma on August 17, 2017:

Didn't realize they were related to carp. Great read!

Linda Crampton (author) from British Columbia, Canada on August 16, 2017:

Hi, John. Thank you for sharing another interesting fact about goldfish! The teeth of goldfish are located in their throat, as you say. They're known as pharyngeal teeth.

John from Sagnay, Camarines Sur, Bicol, Philippines on August 16, 2017:

It's so very interesting. Most especially when goldfish eat their food they have chewing apparatus in their throat (correct me if i am wrong). It's very fascinatinv and easy to breed. Thanks for the info.

Linda Crampton (author) from British Columbia, Canada on August 15, 2017:

I think you're right, Mary. In the future we might look back and wonder how we could have been so cruel to animals. Some of the things that we do and have done to them are horrible.

Thank you very much for the visit and the comment.

Mary Wickison from USA on August 15, 2017:

So many interesting facts I didn't know about the goldfish.

Regarding the misunderstanding of the 3-second memory of goldfish, I'm sure there must be many urban myths that scientists and researchers cringe every time they hear them.

I think people of my age, their first experience of goldfish was at a fair in a plastic bag as a prize, as you say. Along with the piano playing chicken in the perspex box. It used to tap out a tune to get corn when someone put money in.

I wonder how we could have been so cruel and not realized that doing something like that was wrong.

It makes me wonder, what we are doing now that we will look back on and think, "what the hell were we doing".

Wonderful information about the goldfish.

Linda Crampton (author) from British Columbia, Canada on August 15, 2017:

Hi, Heidi. The way that goldfish are sometimes treated is very sad. Thanks for the visit. I always appreciate your comments.

Heidi Thorne from Chicago Area on August 15, 2017:

I, too, have been disheartened by the abuse of goldfish. I also remember them being "given away" as prizes at school fairs when I was a kid. How inhumane and sad, especially given the fact that they do have memory and/or associative learning ability.

Didn't know about their alcohol-producing ability to survive the cold. Interesting.

Love your nature articles! Keep the good stuff coming!

Linda Crampton (author) from British Columbia, Canada on August 15, 2017:

Thanks, Linda. I hope you enjoy having fish in your home if you get them.

Linda Courtney from Bloomsburg, PA on August 15, 2017:

Very informative article. All good information for anyone who is in the market for some fish as I have been thinking about. Thank you!

Linda Crampton (author) from British Columbia, Canada on August 15, 2017:

Hi, Jackie. I'm glad that knowledge never stops! It's interesting to learn new things.

Linda Crampton (author) from British Columbia, Canada on August 15, 2017:

Thank you very much, Bill! I appreciate your visit and comment.

Jackie Lynnley from the beautiful south on August 15, 2017:

I studied goldfish for a long time. Knowledge just never stops for you have fed me so much more. Great info!

Bill Holland from Olympia, WA on August 15, 2017:

See, that's exactly why I love your science series so much. Here's a fish we all think we know tons about, and in five minutes you show us exactly how little we knew. Great information!

Linda Crampton (author) from British Columbia, Canada on August 14, 2017:

Hi, Penny. That's a recent discovery. It's certainly interesting! Thanks for the comment.

Penny Leigh Sebring from Fort Collins on August 14, 2017:

I didn't know that they converted the lactic acid into alcohol. Fantastic information as always!

Linda Crampton (author) from British Columbia, Canada on August 14, 2017:

Thank you very much, Flourish. It's interesting that scientists are finding that some animals have better mental abilities than we thought. Animal behaviour is fascinating!

FlourishAnyway from USA on August 14, 2017:

I loved this and hope that others like me can have new levels of love and respect for goldfish. Animals are much more intelligent than we have given them credit for. Wonderful article!