Goldfish: Interesting and Surprising Facts About a Popular Pet

Updated on July 23, 2019
AliciaC profile image

Linda Crampton is a writer and teacher with an honors degree in biology. She loves to study nature and write about living things.

A veiltail goldfish
A veiltail goldfish | Source

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’re often thought of as attractive but relatively simple creatures. Scientists and enthusiasts have made some interesting discoveries which show that there is more to the animals than is sometimes realized, however.

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.

Carassius gibelio
Carassius gibelio | Source

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.

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.

A giant goldfish from a pond
A giant goldfish from a pond | Source

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".

A beautifully coloured goldfish
A beautifully coloured goldfish | Source

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 goldfish in plastic bags being given as prizes at fairs. 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 the fish healthy and happy in captivity. They should also identify a vet who can provide help for any health problems that develop in the fish.

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

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 can be beautiful—and spend any money that's left over on a large tank and items needed to keep the fish healthy and reasonably happy.

A pearlscale goldfish
A pearlscale goldfish | Source


"Background Information About Goldfish" from the Bristol Aquarists' Society

Four secrets your goldfish is hiding from you from BBC Earth

"Do fish really have a 3 second memory?" from The Naked Scientists (a group based at the University of Cambridge)

Another article entitled "Do Fish Really Have a Three-Second Memory?" from Mental Floss

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

Questions & Answers

    © 2017 Linda Crampton


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      • AliciaC profile imageAUTHOR

        Linda Crampton 

        15 months ago from British Columbia, Canada

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

      • wildbluefrontier profile image

        Nathan M 

        15 months ago from Tucson

        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.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        21 months ago from British Columbia, Canada

        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 le Venerable profile image


        21 months ago from Minnesota

        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.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        22 months ago from British Columbia, Canada

        Thank you very much for the comment, Catherine!

      • CatherineGiordano profile image

        Catherine Giordano 

        22 months ago from Orlando Florida

        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.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        23 months ago from British Columbia, Canada

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

      • Alex Anghel profile image

        Alex Anghel 

        23 months ago from Romania

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

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        23 months ago from British Columbia, Canada

        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.

      • escole61 profile image

        colin powell 

        23 months ago from march

        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.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        24 months ago from British Columbia, Canada

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

      • PegCole17 profile image

        Peg Cole 

        24 months ago from Northeast of Dallas, Texas

        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.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        24 months ago from British Columbia, Canada

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

      • Nancy Owens profile image

        Nancy Owens 

        24 months ago from USA

        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.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        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.

      • CatherineGiordano profile image

        Catherine Giordano 

        2 years ago from Orlando Florida

        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.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        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.

      • MartieCoetser profile image

        Martie Coetser 

        2 years ago from South Africa

        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!

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

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

      • bdegiulio profile image

        Bill De Giulio 

        2 years ago from Massachusetts

        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.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

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

      • profile image

        Peggy Woods 

        2 years ago

        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.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        Thank you for the very interesting comment, moonlake.

      • moonlake profile image


        2 years ago from America

        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.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        Thank you very much, Dora.

      • MsDora profile image

        Dora Weithers 

        2 years ago from The Caribbean

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

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

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

      • nicenet profile image


        2 years ago

        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.


      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        Thanks, Larry. I appreciate your visit.

      • Larry Rankin profile image

        Larry Rankin 

        2 years ago from Oklahoma

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

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        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 Nolial profile image


        2 years ago from Sagnay, Camarines Sur, Bicol, Philippines

        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.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        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.

      • Blond Logic profile image

        Mary Wickison 

        2 years ago from Brazil

        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.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

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

      • heidithorne profile image

        Heidi Thorne 

        2 years ago from Chicago Area

        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!

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

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

      • Linda Courtney profile image

        Linda Courtney 

        2 years ago from Bensalem, PA

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

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

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

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

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

      • Jackie Lynnley profile image

        Jackie Lynnley 

        2 years ago from The Beautiful South

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

      • billybuc profile image

        Bill Holland 

        2 years ago from Olympia, WA

        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!

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

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

      • Penny Sebring profile image

        Penny Leigh Sebring 

        2 years ago from Fort Collins

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

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        2 years ago from British Columbia, Canada

        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 profile image


        2 years ago from USA

        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!


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