Do Fish Throw Each Other Under The Bus?
    By Gerhard Adam | July 12th 2013 12:33 PM | 4 comments | Print | E-mail | Track Comments
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    A recent article "These fish are evidence that humans aren't the only evil animals" began from the presumption that these fish were intentionally injuring others to avoid predation against themselves.

    One problem with this article was the initial silly use of terms like "evil" or "selfish" when clearly that is not what this behavior involved.  As mentioned in the paper, there is nothing cognitively intentional about this behavior so to assign these terms is just more sensationalist nonsense.

    Two-spot astyanaxInstead what we have is an experiment in which these fish were subject to three modes of predation; active search, sit-and-wait, and pecking.  Each type represented different ways in which these fish might be preyed upon, with a fourth category representing a control [a white plastic container].

    In this experiment only the active search mode of predation produced any reaction, which was expected since the other two modes were simply too arbitrary and random to afford any benefit regarding a response from the fish. As a result, it was deemed to be outside the range of traits that would likely be selected for.

    Before examining the active search results it is pertinent to understand that these fish have specialized cells that release a chemical alarm when the skin has been damaged.  This alarm elicits a fear response and antipredatory behavior in fish that are nearby.

    As a result, in the active search experiment, when the predator approached, the fish appeared to become more aggressive towards each other, biting others [which resulted in the chemical alarm being released], and swimming faster.  

    These results were interpreted as:
    This response could reduce an individual's predation risk by making the other (i.e. the attacked) individual more vulnerable to predation.
    In the press article, this gave rise to the notions of selfishness and these fish behaving in an "evil" manner.

    Yet, I would submit that there could be a completely different interpretation of these results, that would suggest cooperative behavior instead.

    In the first place we know that releasing a chemical in water is going to have limited dispersion, so the number of individuals that are exposed and capable of interpreting this danger alert is limited.

    However, there is a more fundamental issue involved here as well.  Since the cue is only released when the skin is damaged, then under ordinary circumstances it would only be present after a fish had already been attacked by the predator.  This would severely limit the utility of such a warning, since it presumes that the predator has already gained several meals before the rest are aware of the danger.

    Similarly the fish cannot release these chemicals by any ordinary physiological mechanism, so it follows that the only way to raise the alarm before the predator kills anyone is to bite each other without inflicting any injury.  In fact, this is precisely what occurred.
    "And tests showed that the fish did indeed release their alarm chemicals after getting bitten (note: the bites didn't draw blood, they only removed scales)."
    While the release of the chemical alarm may indeed make a particular individual more detectable to a predator, it seems odd that if the purpose was to "sacrifice" another individual that they wouldn't attempt to injure them.  After all, adding blood in the water would be an even stronger incentive for the predator to pursue.

    In addition, we find those that had been bitten, swimming off, and then returning.  Again, this seems peculiar if there is a sense that they are being "picked on" or "sacrificed".  Instead, what may well be happening is that they are swimming off, and returning to maximize the amount of chemical alarm being dissipated in the water, so that greater numbers of fish are warned.

    While I certainly can't claim that my version is accurate or correct, the point here is that one must be careful with how such behavior is interpreted and in this case, my concern is that the interpretation is occurring based on a preconceived sense of selfish behavior rather than an objective analysis.


    Spoilsport!  Do you mean that Bob the Killer Goldfish is not really evil after all?

    The title of this article did, though, make me think of this piece of Scottish folk music:

    You Cannae Shove Your Grannie Off The Bus

    Robert H. Olley / Quondam Physics Department / University of Reading / England
    Gerhard Adam
    While I can't speak to individual goldfish, I think it's same to say that the entire species isn't evil.
    Mundus vult decipi
    Bonny Bonobo alias Brat
    Very interesting article Gerhard. Do fish throw eachother or their grannies under the bus?
    I had similar misgivings when I read the "These fish are evidence that humans aren't the only evil animals" article. It made more sense to me that quickly biting off a couple of each others scales, in order to release the alarm chemical, was more like a mutually cooperative and beneficial activity, to make the whole shoal more alert and swim faster and have a better chance overall of survival and escaping the predators. Any alarm chemical released by one individual fish darting around the place, would spread the chemical everywhere and would be very difficult, I would have thought, for the predator to track that individual leaky fish and eat it. 

    I feel that I have been witnessing animal behaviorists using fish in psychological animal behavior experiments and making wrong deductions for decades now, since I studied for my first psychology degree. I will never forget reading an experiment in which researchers trained goldfish to swim from one half of  tank through various automated trapdoor openings to the other half of the tank, in order to escape slightly painful electric shocks after various stimuli warning lights were flashed. 

    They were amazed at how well the goldfish learnt the experiment and then started to test whether the fish would swim through different openings in response to different stimuli. To their amazement the fish quickly learnt to avoid the painful electric shocks and could do this quite complicated behavioral task very well  too. It was something like, flash a red light or flash once and the fish went through the red opening, which suddenly briefly opened to allow the fish to escape the electric shock. Flash a blue light or flash twice and the fish swam through the blue opening, which also had briefly opened just long enough to allow the fish to escape the shock and so on.

    Then the researchers decided to see what would happen if they flashed the lights and the fish did what they were trained to do and then they still gave them the electric shocks, regardless. They did this multiple times to well trained fish and were amazed that in the end, the fish often exhibited a strange comatose like response, adopting a motionless posture, appearing to now be completely disinterested in any flashing lights and openings, no longer responding to them when they appeared, floating with their heads hanging down slightly lower than their tails! An experiment showing that evil scientists also throw their fish under the bus maybe?

    I don't know if you noticed but the original study that the evil fish article linked to was about training Nile tilapia fish to escape predators. The abstract said that 'Globally millions of fishes are released, each year, into the wild to supplement diminishing populations. However, research indicates that less than 5% of these individuals survive, and that one of the major causes of mortality is predation. The objective of the experiment was to develop a protocol to train captive born and reared fish how to avoid predators.' Ha ha, fishes????
    My article about researchers identifying a potential blue green algae cause & L-Serine treatment for Lou Gehrig's ALS, MND, Parkinsons & Alzheimers is at
    Thanks for this interesting read, Gerhard.

    I've seen this type of writing frequently from students who are majoring in something other than science, and can't help but wonder if the professional and semi-professional writers who do it are motivated the same way.  Because nonscientists tend to think science is BORING, they enjoy any science which seems jazzy, like attributing "evil" to otherwise non-self-aware organisms, like the fish.

    While I want to actively combat this tendency to pseudoscience in students, it's hard because it means eliminating or discouraging what little science interest it may have caused.