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Cichlids, Stingrays, and Goldfish: The Mind of a Fish

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

A veiltail goldfish

A veiltail goldfish

The Capabilities of Fish Brains

For many people, it may sound strange to think that a fish has a mind. The results of experiments suggest that at least some fish do have a mind. We appear to be underestimating the abilities of the animals. Fish have a different anatomy and physiology from us, and they live in a different environment, but in at least some individuals that doesn’t mean that they lack intelligence.

A recent experiment has shown that some cichlids and stingrays can add and subtract numbers by 1 up to the number 5. Another experiment has shown that with the help of technology goldfish in a tank on wheels can control the direction of a trip through a room in order to receive a treat. One fish used its newfound ability to explore beyond the room.

Cichlid Facts: Pseudotropheus zebra

Cichlids belong to the family Cichlidae. The family is large and diverse. Some members of the family are kept as pets. Wild species live in Central and South America, Africa, Southeast Asia, and India. They inhabit fresh water or in some cases brackish water. Many cichlids are just a few inches in length, but some are larger than a foot. According to SeaWorld in the United States, new species of cichlids continue to be discovered every year.

The cichlid species used in the experiment described below was Pseudotropheus zebra, or the zebra mbuna. Confusingly, this fish has been given multiple scientific names, including Maylandia estherae and Metriaclima estherae. The species is native to Africa and is around five inches in length. It's shown in the video above.

Ocellate river stingray (Potamotrygon motoro)

Ocellate river stingray (Potamotrygon motoro)

Stingray Facts: Potamotrygon motoro

The other species used in the first experiment that I describe was Potamotrygon motoro. It's a freshwater stingray that has a variable appearance and several common names, including the ocellate river stingray. It bears light spots surrounded by a darker colour. The surrounding area of its body may be sand-coloured, brown, or blue-grey. I've chose a light brown form for the illustration above because a photo in the scientific publication of the study shows that the animals in the experiment were this colour.

The species belongs to the class Chondrichthyes, like sharks. The fish in this class have a skeleton made of cartilage instead of bone. Potamotrygon motoro lives in South America. Adults can be very large. According to various sources, males are said to reach 20 to 36 inches in length. The fish has a venomous spine on its tail. The species isn't described as aggressive, but it will use its venom to protect itself if it feels threatened. As the quote below says, stingrays sting to defend themselves. It's possible that someone may accidentally disturb one in the wild, however, which may cause the animal to believe that it's being attacked.

Stingrays strictly sting out of defense, never as an offensive maneuver.

— California State University Long Beach

Ability of Cichlids and Stingrays to Count

Researchers at the University of Bonn have discovered that some cichlids and stingrays can both add and subtract by 1 in the range of numbers 1 to 5 after a training period. Since fish don't understand human language, it might be wondered how the scientists could tell them to perform arithmetic. The researchers did this by placing coloured shapes in front of the fish. The shapes were projected and provided instructions in a pictorial form. The experiment is summarized below.

  • The fish were first shown a picture of either blue shapes or yellow shapes for five seconds.
  • The blue shapes were circles, squares, and triangles. A variable number of the shapes was shown in the trials.
  • The yellow shapes were also circles, squares, and triangles. A variable number of the shapes was shown in the trials.
  • The blue shapes told the fish "Choose a picture from the next two that are shown that has one more shape than this picture," or to perform addition.
  • The yellow shapes told the fish "Choose a picture from the next two that are shown that has one less shape than this picture,' or to perform subtraction.
  • The fish chose a picture by swimming to it.

The fish were not trained to recognize 3+1 or 3-1. After they had been trained to do other arithmetic problems, they were able to go to the correct picture once this test was presented. This demonstrated that they were actually performing arithmetic. Other precautions were also taken in the experiment to ensure that the fish were actually performing addition or subtraction.

Six of the eight cichlids and four of the eight stingrays were classified as successful in learning the task. The researchers say that although the percentage of successful stingrays was lower, "individual performance of stingrays generally exceeded that of cichlids, with more individuals performing significantly above chance level in all individual test scenarios."

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Analyzing the Results of the Experiment

The results of the experiment are impressive. Only eight cichlids and eight stingrays were involved in the experiment, however. It should also be noted that some of the cichlids had been used in other cognition experiments in the laboratory. In other words, their brains had already been exercised in a particular way. The abilities of their brains are still impressive, though. It's also interesting to see that although the stingrays as a group weren't as successful as the cichlids, individual stingrays were more successful than the cichlids. Addition was easier for all of the fish than subtraction.

As the researchers point out, the arithmetic skills learned in the experiment may not be very important in the real life of the animals. This might be an incorrect assumption, however. Though the researchers took multiple precautions in order to get accurate results, it's hard to design a suitable experiment when we don't know exactly what an animal is sensing or how its brain works. It's interesting to note that once the arithmetic skills had been learned by the fish, they were retained.

Fish don't have a cerebral cortex, or the part of our brain that is associated with our higher functions. This has meant that some people have dismissed their mental abilities. Birds don't have a cerebral cortex, either, but some (such as members of the crow family) are intelligent animals. Researchers have discovered that their thinking ability is located in the pallium of their brain. Fish also have a pallium. Just because an animal doesn't have a brain resembling ours doesn't mean that it is unintelligent. Fish may have more mental abilities than we realize.

Goldfish are one of the longest-living fishes out there, with the oldest recorded living goldfish reaching the age of 49. The main reason why so many goldfish die young is that they aren’t kept in the proper conditions.

— Kali Wyrosdic, PetMD

Goldfish Information

Goldfish (Carassius auratus) are very popular as pets. They are a member of the carp family, or the Cyprinidae one, and originated in Asia. They are believed to have developed from the Prussian carp (Carassius gibelio). Different goldfish varieties have been created by selective breeding.

Unfortunately, the brain power of the fish is sometimes ridiculed. A popular legend that scientists repeatedly deny is that a goldfish can only remember things for three seconds. In fact, goldfish have a good ability to learn, and they can remember some things for at least three months.

When kept as a pet in a small tank, goldfish are small animals. If they are moved to a larger body of water, they can grow much bigger. Goldfish have been known to be well over a foot in length and to weigh several pounds.

Interesting Behaviour in Goldfish

Scientists at Ben-Gurion University of the Negev in Beer-Sheva, Israel, placed six goldfish in separate tanks. Each tank was placed on a computerized cart that had wheels. The carts had a camera, which was focused on the tank and detected the movement of the fish. The robotic cart moved in the direction that the fish swam. The fish learned to move the cart towards a pink disk in a room, which resulted in them being given an edible treat.

The scientists said that all of the goldfish learned to steer the cart to the disk, but some learned the technique quicker than others. Once the fish had learned how to navigate, the researchers started the cart in different positions in the room. They also placed cards of different colours on the wall and moved the pink card to a different location. The animals still guided their cart towards the pink card, showing that they had a plan in mind.

The scientists let one goldfish explore the building beyond the room. He or she was so good and quick at navigating that they "started to sneak away," according to one of the scientists.

During their first sessions, the fish averaged about 2.5 successful trips to the target. During their final sessions, fish averaged about 17.5 successful trips. By the end of driver’s ed, the animals also took faster, more direct routes to their goal.

— Maria Temming, ScienceNews

The Abilities of Fish

Although fish don't have a mind that is as advanced as ours, the new abilities that scientists are discovering are very interesting. We seem to have been underrating their brain power, at least with respect to the species mentioned above. We are learning that just because an animal's brain looks different from ours does not mean that the animal is without the ability to reason and to learn to at least some extent. The lives and brain abilities of animals are interesting to explore.

References

  • Cichlid information from SeaWorld Parks and Entertainment
  • Facts about the South American freshwater stingray from FishBase (a database of fish information)
  • Stingray information from the University of California Long Beach
  • Goldfish facts from PetMD
  • (At least some) fish can calculate: Press release from the University of Bonn via ScienceDaily
  • "Cichlids and stingrays can add and subtract "one" in the number space from one to five" from Nature Scientific Reports
  • Goldfish can navigate using a robotic cart from ScienceNews
  • New insights on navigation mechanisms in goldfish (Abstract and Sections Snippets from Behavioural Brain Research, Elsevier)

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2022 Linda Crampton

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