I had a really old tetra fish, around 7 years old, who was getting weak. The other fish were helping him get food and were supporting him whenever he was swimming around. A few days later, the fish died. Is there some way that fish are able to figure out that one is weak and will be dying soon?


4 Answers 4


A study from Yale indicated that tadpoles would stay away from a sick tadpole because they knew they would become infected if they were around it. Yale Study Although this doesn't apply directly to fish, this is found in the animal kingdom a lot. Runts being kicked out of the litter. Mothers licking the wounds of their children. I wouldn't think that a fish would have the capacity to do this, but if a tadpole can, I wouldn't see why not.

To answer your question: "Is there some way that fish are able to figure out that one is weak and will be dying soon?". Yes, you could do your own study, by monitoring healthy fish and taking notes; then drop in a fish that is unhealthy and seeing how they react. If you can recreate your situation multiple times you have support for your hypothesis. Although introducing a dying fish may not be the same as a "friend" to to the healthy fish dying.

Good luck in your findings!

  • the link has died,the study do probably not inklude all variables tadpoles do not stay away from sick tadpoles at all quite the oposite they eat them(i have observed this behaviour every year for more than 25 years) Commented May 31, 2020 at 16:36

We've had two gold fish for several years. One fell ill and, despite our best efforts, just continued to decline. We observed how the other fish took care of it's tank mate during the final couple of days... up until the dying fish went into a hollowed out rock to die. Once that happened the other fish stayed away. After it died though, the other fish swam into the rock and back out.

There is absolutely no question in my mind the BOTH fish knew exactly what was happening.


I have 9 mickey mouse Platys. So I decided to get a couple more fish I got 2 guppies a male and a female . I don’t care what anyone says or what studies were done ect ect . My boy guppy absolutely loved her to death he was by her side 24 -7 no exaggeration. They had fry and I saved 2 ( omg so cute)z!!! Well about a week ago I noticed that mama guppy wasn’t swimming right . Turns out she had swim bladder disease . Absolutely broke my heart , so I put her in the floater tank so she could rest and her hubby was right by her face the entire time . Finally I decided to put him in with her because they literally both looked so sad . The second I put him in he swam over to her and just payed down right next to her for 3 days . Fish are much smarter than people think . I definitely think she knew and so did he . She would lay in my hand and just look at me so sad . My poor guppy passed a few hours ago . Everyone is like omg it’s just a fish . Well I loved her and I am very sad over her passing and me not being able to help her get better . 😥😭thank u for listening. i’m very sorry .


The majority of the animal kingdom, including fish but not dolphins, do not have a sense of identity or self-recognition [1]. So they likely do not experience an abstract awareness of their eminent demise.

While they may not be abstractly aware of their demise, all vertebrates have a nervous system and experience pain and stress. Even animals that do not have self-recognition have been known to go to great lengths to attempt to survive.

[1] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC33317/

  • 1
    That reference is for recognizing their own image in a mirror, not sure I would lump "a sense of identity" in the same category. Commented Aug 18, 2014 at 11:59
  • That's a common measure of abstract thinking, but I know what you mean. Commented Aug 22, 2014 at 3:43
  • 1
    Including fish but not dolphins? Dolphins aren't fish
    – Gary
    Commented Nov 16, 2014 at 16:47
  • 1
    @Gary The sentence is ambiguous, you're just pointing out one possible meaning. It seems that the author of that answer is aware that cetaceans are not fish. The reason why dolphins were explicitly mentioned was that elephants and dolphins are generally accepted as only animals beside human to possess advanced abstract thinking and self-recognition. Commented Apr 2, 2015 at 12:24
  • The original question asks if the fish understood that their friend was about to die. This answer doesn't relate the self-aware aspect to sensing the health of another animal.
    – Arcite
    Commented Jul 29, 2015 at 14:12

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.