Archerfish Puts Spit Stream in Overdrive to Knock Down Prey

underwater photo of a silver fish with black stripes

Biological Strategy

Spotted archerfish

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Image: David Clode / Unsplash / Free non-commercial use

Distribute Liquids

Liquids include water, as well as body fluids such as blood, gastric juices, nutrient-laden liquids, and more. To survive, many living systems must move such liquids within themselves or between locations. Because of their properties, liquids tend to disperse unless they are confined in some way. To address this, living systems have strategies to confine fluids for transport, and to overcome barriers such as gravity, friction, and other forces. Some of these same barriers also provide opportunities. Trees and giraffes face the same challenge: how to move fluids (water and blood, respectively) upward against gravity. But their strategies are quite different. The tree moves water using capillary action and evaporation, possibly due to water’s properties of polarity and adhesion. The giraffe’s tight skin provides pressure to assist in blood circulation. and keep blood from pooling in the legs.

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Capture, Absorb, or Filter Organisms

Many living systems must secure organisms for food. But just as one living system must capture its prey to survive, its prey must escape to survive. This results in capture and avoidance strategies that include trickery, speed, poisons, constructed traps, and more. For example, a carnivorous plant called the pitcher plant has leaves formed into a tube that collect water. Long, slippery hairs within the tube face downward. When insects enter the tube seeking nectar, they lose their footing and slide inside, unable to climb out and escape being eaten and digested by the plant.

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Fish

Class Agnatha (“without jaws”), Class Chondrichthyes (“cartilage fish”), Superclass Osteichthyes (“bone fish”): Sharks, eels, snapper, hagfish

The fish are a diverse group, comprising multiple classes within Phylum Animalia. The most well-known classes are Chondrichthyes, which has sharks and rays, and superclass Osteichthyes, which has all bony fish like cod and tuna. Unlike other vertebrates, fish only live in water. They use special adaptations like fins, gills, and swim bladders to survive. Most are ectothermic, meaning their body temperature depends on the water temperature around them. Over half of all vertebrates are fish. They’re found from the bottom of the sea to high mountain lakes.

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A rush of water enhances forcefulness of nature’s super-soaker.

Archer fish are known for striking down prey in vegetation surrounding their habitats. These fish do so by propelling water in the form of a jet stream that strikes its prey with enough force to knock it off the vegetation and into the surrounding water. It was originally believed that the fish were capable of producing such strong jet forces because of some internal structure or mechanism but new studies show that the force is actually amplified outside of the fish’s body. During the propagation of the jet, the fish modulates the stream to create a gradual increase in the accumulation of water at the head of the jet (i.e., mass is directed to accumulate at the head of the jet as it moves). This increase in mass towards the head of the jet also increases its velocity. The force that these modulations create when the jet hits the prey outside of the water is nearly six times greater than the force of the water that leaves the fish’s mouth.

To see the archer fish in action and learn more about this creature, check out this video by KQED Deep Look and this video by NYTimes ScienceTake.

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Last Updated February 1, 2017

References

Book

Animal Architecture

22/04/2014 | Ingo Arndt

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Reference

Journal article

How Archer Fish Achieve a Powerful Impact: Hydrodynamic Instability of a Pulsed Jet in Toxotes jaculatrix

PLoS ONE | 24/10/2012 | Alberto Vailati, Luca Zinnato, Roberto Cerbino |

Andrew Pelling

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Reference

Journal article

Archerfish Actively Control the Hydrodynamics of Their Jets

Current Biology | 05/09/2014 | Peggy Gerullis, Stefan Schuster

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