Archer fish hunt insects with water jet 6 times stronger than their muscular power

Oct 24, 2012
Archer fish hunt insects with water jet 6 times stronger than their muscular power
This is a still image of archer fish swimming, 1632x1224. Credit: L. Zinnato.

Archer fish knock their insect prey out of overhanging vegetation with a jet of water several times more powerful than the fish's muscles. New research now shows that the fish generate this power externally using water dynamics rather than with any specialized internal organs. The research, published Oct. 24 in the open access journal PLOS ONE by Alberto Vailati and colleagues from the University of Milan, provides the first explanation for how archer fish can generate such powerful jets to capture their prey.

Other animals like chameleons and salamanders store energy in in their bodies and abruptly release this stored energy to project their tongues at high speeds, but previous studies on archer fish have ruled out such specialized organs as the source of the powerful water jets.

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This is a movie of archer fish firing a flurry of blows at prey. Credit: L. Zinnato

The authors of the current study used high-speed video recordings of archer fish knocking insects out of overhanging plants to study the mechanics of the water jet and found that the fish could modulate the velocity of the jet to create a single large water drop that hit the prey with a large force. According to the authors, this approach avoids the evolutionary costs needed to develop special internal structures to store these large amounts of energy.

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This is a slow-motion movie of archer fish shooting at prey and eating it when it falls into water. Credit: A. Vailati

"The origin of the effectiveness of the jet squirted by archer fish has been searched for inside of the fish for nearly 250 years. The striking finding of our work is that a large amplification of muscular power occurs outside of the fish and leads to a very powerful impact of the jet with the prey" says Vailati.

Explore further: Researchers collect soil samples from around the globe in effort to conduct fungi survey

More information: PLoS ONE 7(10): e47867. doi:10.1371/journal.pone.0047867

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gwrede
1.8 / 5 (5) Oct 25, 2012
The striking finding of our work is that a large amplification of muscular power occurs outside of the fish and leads to a very powerful impact of the jet with the prey" says Vailati.
Sigh. This sounds as scientific as most of the pseudo-science explanations of ESP, Kirlian photography and the electric universe.

Amplification of muscular power outside of the fish, my butt!
ValeriaT
1 / 5 (4) Oct 25, 2012
Such a striking finding could lead to a new generation of even more effective perpetuum mobiles - especially those based on amplification effect of water. Or it could lead to enforcing of stereotypes about generally poor scientific level of articles dealing with biomechanics, especially those published with Italian authors in PLOS journal.
albertovailati
5 / 5 (3) Oct 25, 2012
gwrede and ValeriaT, dealing with biomechanics requires some basic knowledge of the principles of physics. In physics energy is a conserved quantity, but power definitely not! Human beings and primates have mastered the ability of using tools to amplify muscular power. For example,would you shoot an arrow by using the direct action of your arm? I assume that you would be better off by using a bow...
If you mind reading our paper carefully and looking at our data, we will be glad to answer any question based on solid technical arguments, and not on prejudice
albertovailati
5 / 5 (2) Oct 25, 2012
So, are you implying, during spit some accumulation of the muscle energy happens there? And it's released back after spit? And this accumulation is done with neighboring water outside of fish?

The energy gets transferred from the muscles to the jet and is distributed along the jet. The increasing velocity of the jet, however, determines the accumulation of the energy at its tip. At the impact the energy is mostly concentrated at the tip of the jet and is released abruptly at the impact.
Yes, I did it. How the power of muscles can be and was actually measured?

The power of the muscles was estimated from reference data, as described in the methods. The typical maximum mass-specific power output of the muscle of a vertebrate is of the order of 500W/kg. For the estimate of the mass of the muscles involved in the spitting process we used the results published by Elshoud and Koomen (our ref.10)
gwrede
4 / 5 (1) Oct 27, 2012
Alberto, my problem was not your science or methods, it was with the way the sentence was written.

It gets already much better if you replace the word "amplification" with either "focusing" or "concentration".

Think about it. Energy can be stored (as in an archer's bow), and focused (as with a looking-glass, or when you tear paper all of the energy is focused at the point of tearing). But if you want to amplify energy, you need an energy input from the side, as in a stereo amplifier, which either needs batteries or mains current.

I know from my own experience it's hard to write in English when it's your second or third language.
ValeriaT
4.5 / 5 (2) Oct 27, 2012
It gets already much better if you replace the word "amplification" with either "focusing" or "concentration".
You're fully right, but the process which concentrates the muscle POWER would require some accumulation of energy in time (released spring or similar mechanism).

If the duration of spit is comparable with the time of jet impact, then not only any ENERGY is amplified, but even no amplification of POWER occurs there. The only quantity which is apparently amplified here is the SPEED of jet - which is higher, than the speed of muscles, which were used for spitting. This is indeed a trivial consequence of Bernoulli equation and it doesn't require any specialized theory or surprised article for its explanation. Every spiting works like pumping of fluid through nozzle and no accumulation of power occurs here, its amplification the less.

The voting trolls may downvote me as they wish, but I do understand my subject quite well.
albertovailati
5 / 5 (1) Oct 27, 2012
But if you want to amplify energy, you need an energy input from the side, as in a stereo amplifier, which either needs batteries or mains current. I know from my own experience it's hard to write in English when it's your second or third language.


gwrede, I fully agree with you on the importance of using the right words. In classical physics there's no such a phenomenon as the amplification of energy mentioned by you. Indeed, you might have noticed that in our paper we discuss the amplification of power.
If you're genuinely interested in understanding more about the amplification of power in biomechanics, I address your attention to the work by a leading authority in the field, which incidentally is also a native speaker of English: R. McNeill Alexander, Functions of Elastomeric Proteins in Animals pp. 1-14B, (Cambridge University Press, 2003)
albertovailati
5 / 5 (1) Oct 27, 2012
If the duration of spit is comparable with the time of jet impact, then not only any ENERGY is amplified, but even no amplification of POWER occurs there.


The duration of the spit is NOT comparable with the duration of the impact (see movie S1 and data in our paper).

The only quantity which is apparently amplified here is the SPEED of jet - which is higher, than the speed of muscles, which were used for spitting. This is indeed a trivial consequence of Bernoulli equation and it doesn't require any specialized theory


The "amplification of speed" through a nozzle mentioned by you does not have anything to do with the Bernoulli equation. You are probably referring to the continuity equation. In any case, our work deals with the propagation of a non-stationary jet. The axial modulation of the velocity gives rise to an accumulation of momentum at its tip. The process is not very complicated, but its understanding requires some knowledge of the laws of fluid dynamics
ValeriaT
1 / 5 (1) Oct 27, 2012
The axial modulation of the velocity gives rise to an accumulation of momentum at its tip. The process is not very complicated, but its understanding requires some knowledge of the laws of fluid dynamics
I can simulate fluid dynamics.. Go on...

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