Knifefish sacrifice energy conservation for enhanced prey perception, research has suggested.
The fish, which uses weak electromagnetic fields to detect its prey, alters its position in the water so that it is inclined to 30° - causing increased drag as it moves, and producing twice as much water resistance compared to the same fish with no tilt.
The payoff for such reckless energy burning is an enhanced sensory area, allowing the fish to detect the impulses of small fish and insects over a much wider area than if they were swimming horizontally.
The action has been compared by the authors of the study to be similar to riding a push bike whilst standing up; although you increase your field of view over the handlebars, you need to fight more drag and air resistance.
The cost of the tilt is counterbalanced by the degree of increased sensory enhancement. However, beyond a certain point, the angle of the tilt produces more of an energy cost than is gained by the extra sensory range.
Adapting for success
As well as providing clues into why knifefish are so successful in the wild, the conclusions of the research also give strong indications into the drivers behind the evolution for adjustable regions of prey sensitivity – explaining why animals like humans have ended up with moving eyes and heads that turn.
The study also raised the possibility that the elongate shape of knife fish (Apteronotus) may have evolved as a direct result of the drag factor created by this unusual hunting position.
Although hard for us humans to fully appreciate, water resistance is around 1000 times greater than air resistance, and even tiny changes can have a huge implication for underwater organisms – as anyone who has tried to wade through the sea in a hurry will be able to attest!
For further reading, the research article can be viewed in full at www.ploscompbiol.org/article/info%3Adoi%2F10.1371%2Fjournal.pcbi.1000769