An orange goldfish swimming among green plants in a clear home aquarium beside a bright window
AI-generated image, not a photograph of a real person or place.
fishthatthink

WHAT THE EXPERIMENTS SHOW

More going on
behind the eyes.

NOT 3 SECONDS goldfish remember for months

  • Memory that lasts
  • Tools on the reef
  • A face in the mirror
  • Small brains, real thinking

Fish are not swimming blanks.

Researchers have trained goldfish to press a lever at the right hour, filmed wrasse smashing clams on rocks and watched a reef fish scrape a mark it could only see in a mirror. Here is what those studies found, and where scientists still argue.

Updated

Rate a claim

THE SHORT ANSWER

Fish learn, remember
and solve problems.

A 2015 review found fish cognition often
matches or exceeds that of other vertebrates.

MEMORY

Months, not seconds

In experiments at Plymouth University, goldfish learned to push a lever for food, and to push it at the right hour when it only worked for one hour a day.

Rate the claims

THE MIRROR

A mark only a mirror shows

In a 2022 study, 14 of 14 cleaner wrasse given a brown throat mark scraped their throats, but only when a mirror was there to show it.

See the numbers

TOOLS

A rock as an anvil

Graphic tuskfish in New Caledonia carry clams to rocks and coral heads and strike them to break them open, filmed making up to 28 strikes in one bout.

Read the studies well

A QUICK CLAIM CHECK

How strong is
the evidence?

Pick a popular claim about fish to see what the research says. The bar shows how firmly the studies on this page support it.

Claim check

Choose a claim
Goldfish forget in 3 secondsA myth

Goldfish can retain memories for at least three months and can be trained, according to work at Plymouth University reported by BBC Wildlife.

Fish can learn a feeding timeWell shown

Goldfish learned to nudge a food lever during the one hour a day it worked, a skill called time-place learning.

Some fish use toolsSeen in the wild

Graphic tuskfish were filmed using rocks and coral heads as anvils to break open bivalves. The authors suggest tool use may be widespread in wrasses.

A fish knows itself in a mirrorDebated

Cleaner wrasse pass the mark test, but scientists disagree on what that means: either the fish are self-aware or the test itself needs rethinking.

Fish can sense harmWell shown

Rainbow trout have nerve endings that respond to heat, pressure and acid, and a noxious substance on the lips changed their behaviour for a prolonged time.

Sources: Kohda et al. 2022 (PLOS Biology); Pryor and Milton 2019 (Journal of Fish Biology); Sneddon et al. 2003 (Proceedings of the Royal Society B); BBC Wildlife on Plymouth University goldfish work.

Based on the studies and sources listed at the bottom of this page. Research on animal minds keeps moving, so treat this as a snapshot.

TWO NUMBERS WORTH KNOWING

Small brains,
clear results.

One figure from the mirror test,
one from a goldfish memory experiment.

14/14

Marked cleaner wrasse that scraped the mark

New fish given a brown throat mark all scraped their throats, but only with a mirror present. Blue and green marks did not trigger scraping, and seeing another marked fish did not either.

MIRROR TEST · PLOS BIOLOGY 2022

3+ months

How long goldfish can hold a memory

BBC Wildlife reports that goldfish can retain memories for at least three months, can be trained and can learn when food is available.

MEMORY · PLYMOUTH UNIVERSITY

The mirror result is argued over. The 2022 paper notes that conservative readings of earlier data limit convincing mirror self-recognition to great apes; its authors say the wrasse results challenge that.

FOUR WAYS TO READ A FISH STUDY

Curious, but
careful.

A wrasse on a sandy reef floor beside a flat rock scattered with broken clam shells
AI-generated image, not a photograph of a real person or place.

Headlines about clever animals travel fast. These questions help you judge what a study really showed.

  1. Count the fish

    The 2022 mirror study tested 14 new fish to answer criticism of an earlier study. Check how many animals were tested, and whether a result was repeated.

  2. Look for the controls

    Good tests rule out other explanations. The wrasse did not scrape for blue or green marks, or after seeing another fish with the same mark.

  3. Separate seeing from meaning

    Researchers agree the wrasse scrape the mark. They still argue over whether that proves self-awareness.

  4. Check wild against lab

    Tuskfish tool use was filmed on a reef. Lever and mirror tests happen in tanks. Both kinds of evidence matter.

WHY IT MATTERS

What fish feel
shapes how we treat them.

A small blue and black striped cleaner wrasse facing its reflection in a mirror set against the glass of an aquarium
AI-generated image, not a photograph of a real person or place.

Biologist Culum Brown argues that there is a large gap between how clever people think fish are and the scientific reality, and that this perception guides policy. His 2015 review concluded that fish experience pain in a manner similar to other vertebrates.

In UK law, the Animal Welfare (Sentience) Act 2022 defines an animal as any vertebrate other than humans, any cephalopod mollusc and any decapod crustacean. Fish are vertebrates, so they fall within that definition.

Questions

Questions people ask

Do goldfish really have a three-second memory?

No. BBC Wildlife reports that goldfish can retain memories for at least three months, can be trained, and in Plymouth University experiments learned to press a lever for food at the one hour a day it worked.

Can a fish recognise itself in a mirror?

Cleaner wrasse pass the mark test: in a 2022 study, 14 of 14 fish scraped a brown throat mark only when a mirror was present. Whether that proves self-awareness, or shows the test needs rethinking, is still debated.

Do any fish use tools?

Yes. Graphic tuskfish in New Caledonia use rocks and coral heads as anvils to break open clams, with one fish filmed making 28 strikes on two anvils in six minutes.

Can fish feel pain?

A 2003 study found nerve endings in rainbow trout that respond to damaging heat, pressure and acid, and a noxious substance changed their behaviour over a prolonged period. A 2015 review concluded fish experience pain in a manner similar to other vertebrates.

Are fish covered by UK animal sentience law?

The Animal Welfare (Sentience) Act 2022 defines an animal as any vertebrate other than humans, plus cephalopod molluscs and decapod crustaceans. Fish are vertebrates. For what the law requires in a specific case, check the official text.

Sources

Where the facts come from

  1. Brown C (2015) Fish intelligence, sentience and ethics. Animal Cognition 18:1-17
  2. Kohda M et al. (2022) Further evidence for the capacity of mirror self-recognition in cleaner fish. PLOS Biology
  3. Pryor KJ, Milton AM (2019) Tool use by the graphic tuskfish Choerodon graphicus. Journal of Fish Biology
  4. Sneddon LU et al. (2003) Do fishes have nociceptors? Proceedings of the Royal Society B
  5. BBC Wildlife (Discover Wildlife): Do goldfish really only have a 3 second memory?
  6. legislation.gov.uk: Animal Welfare (Sentience) Act 2022, section 5

ABOUT THIS NAME

Interested in leasing fishthatthink.com?

fishthatthink.com is part of the DoodleSale portfolio. It isn't in an auction right now, but you can ask about leasing it.

Ask about this name