Juvenile striped eel catfish form a coordinated, roiling ball to avoid predation

Both Matthew and reader Dom sent me this link to The Colossal describing and showing another amazing animal behavior, this time in the striped eel catfish (Plotosus lineatus), a smallish species (average size about 14 cm) found in the Indian and Pacific Oceans, as well as the Mediterranean where it’s a recent invader. It’s the only catfish associated with coral reefs.  It’s also venomous, with a poison spine on the dorsal fin and each of the pectoral fins, which is reported to have been “fatal”, apparently to at least one human.

While adults are solitary or occur in small groups, the juveniles form schools like the one shown below, comprising 100-150 individuals.  As the report below recounts (click on screenshot), and the videos underneath show graphically, the youngsters swim in roiling balls of fish, with each individual heading towards the bottom and then back up again. (The video was filmed in Bali.) They apparently gather like this for protection, as younger fish are only lightly venomous and could be taken by predators who apparently avoid adults. (Note the striking striped coloration, which may well be “aposematic“: a pattern warning that the bearer is dangerous or distasteful.)

Why they move down and up again is anyone’s guess. I had two ideas: it gives everyone a chance to forage on the bottom while they stay together as a mass, or it makes their pattern more obvious to predators. Or it could be both.

The video comes from the Abyss Dive Center in Bali:

I found another two-minute video that also suggests that they move like this so all individuals can forage.  And be sure to see what happens one minute in, when they rise from the sea floor all together, writhing like a giant jellyfish:

Here are two photos from the Monaco Nature Encyclopedia. The first is an adult, the second a school of juveniles hiding in a reef.

© G. Mazza


© Sebastiano Guido


  1. ThyroidPlanet
    Posted January 27, 2020 at 1:24 pm | Permalink

    Something tells me Ze Frank will explain this soon.

  2. Rita Prangle
    Posted January 27, 2020 at 1:42 pm | Permalink

    That looks formidable!

  3. GBJames
    Posted January 27, 2020 at 1:45 pm | Permalink


  4. Mark R.
    Posted January 27, 2020 at 1:51 pm | Permalink

    It’s a catfish murmuration. I loved it when they took off up the water column- psychedelic, man.

  5. Posted January 27, 2020 at 2:01 pm | Permalink

    Cool! Last photo – Catfish pretending to be a cactus!

  6. Joe Dickinson
    Posted January 27, 2020 at 2:11 pm | Permalink

    For me, the effect in that first video is like some large, multi-legged animal walking along the bottom. If predators that might take individual catfish see it that way, you can understand why that might be a pretty effective time deterrent.

  7. JezGrove
    Posted January 27, 2020 at 2:17 pm | Permalink

    Looking at some of these photos and videos (and many others on this site) I get the feeling that Sci-fi writers and directors lack imagination.’

  8. grasshopper
    Posted January 27, 2020 at 2:36 pm | Permalink

    I was stung in the thumb by one of these beasties in the early days of my two-year stint on a prawn trawler which trawled along the east coast of Australia, just north of Byron Bay. The catfish were known locally as “footballers”, because “they wear a striped jacket.”

    The pain from the sting was like how it feels after you have accidentally struck your thumb with a hammer, for the second time.

    There was only paracetamol in the first aid kit, and the skipper said that some people have been known to go into the engine room and work battery acid into the wound in an attempt to do something, anything, to mitigate the pain. I declined to follow that advice.

    Unfortunately, people would break into the trawlers when moored in harbour and steal the stronger pain-killers, and even destroy inflatable life-rafts in their search.

    • infiniteimprobabilit
      Posted January 30, 2020 at 5:47 am | Permalink

      Catfish can sting? Charming!

      Oh, I see you said it was in Australia. That explains it. In Oz, every bloody thing can sting, bite or otherwise ruin your day… 😉


  9. Ken Kukec
    Posted January 27, 2020 at 3:01 pm | Permalink

    Olympic-grade synchronized swimming.

    • Jenny Haniver
      Posted January 27, 2020 at 3:30 pm | Permalink

      Esther Williams coulda learned some routines from those fish.

  10. Posted January 27, 2020 at 4:17 pm | Permalink

    Your catfish are making my cat hungry. She likes to watch fish, birds, and/or cats whenever they appear on the screen.

  11. phar84
    Posted January 27, 2020 at 4:27 pm | Permalink

    Why speculate when researchers can introduce predators and answer why the formation. It may not even be a defense mechanism.

  12. Warren Johnson
    Posted January 27, 2020 at 4:34 pm | Permalink

    Maybe 60 years ago, when I was a teenager, I occasionally saw a similar ball of tadpole size catfish moving over shallow water in a fresh water lake in central Minnesota. Not foraging but moving languidly in a pretty tight ball. Surely fresh water ichthyologists must know something about this behavior. Got any at UC?

  13. Posted January 27, 2020 at 4:45 pm | Permalink

    Well, they are a ‘squee’ since they are rather adorable. Too bad they are invasive though.

  14. Posted January 27, 2020 at 6:55 pm | Permalink

    It’s as if the school is acting like a giant rotating radula, or, even better, a belt sander!

  15. Кузман
    Posted January 27, 2020 at 8:39 pm | Permalink

    Dang, that’s neat. It reminds me of the tatarigami from the beginning of Mononoke Hime.

    • Кузман
      Posted January 27, 2020 at 8:41 pm | Permalink

      Copy/paste has failed me. Let’s try that link one more time.

  16. Posted January 28, 2020 at 4:41 am | Permalink

    I immediately thought of the penguin huddle when I saw this… fascinating – & thanks to Jerry for adding the extra information!

  17. Posted January 28, 2020 at 11:15 am | Permalink

    Astonishing. How closely related would the individual fish be?

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