Fitting in

Fish evolved to adapt to their swimming environments  

Published: Monday 15 March 2010

imageA liquid always tries to fill the space it gets; humans adapt to the freezing temperatures of Greenland and to the near-burning heat of Africa; birds sing louder to be heard in a noisy locality. What about the fish?

Well, fish evolve by changing their shape to swim more efficiently in the waters they inhabit. For example, a salmon in a narrow fish farm might learn to move as slowly as an eel when left with no other option. But fish evolve slowly; the change is not easy to document.
Hydrodynamics and biofluid specialists at the Saint Anthony Falls Laboratory in the University of Minnesota, usa, demonstrated the possibility. They designed a fish that had the sleek, powerful shape of a mackerel and could either swim like a real mackerel or copy the wriggling motion of an eel. Then they developed an eel that could also beat its tail like a mackerel. Both types were made to swim in two virtual swimming environments: one which required water movements similar to those generated by the slower eel and the other which resembled that produced by the faster mackerel.

The study, published in the January 1 issue of the Journal of Experimental Biology, found that the mackerel did well swimming like an eel in confined waters and that the eel swam as swiftly as a mackerel in open waters. The most efficient swimming gait is assumed to spend as little energy as possible. The idea behind the experiment is that the fish will stick to this basic principle even if it means evolving into a more convenient shape. This study thus explains the evolution of fish in light of adaptation: mackerels are mackerels and eels are eels because of the waters they inhabit.

“An important application of the study is in designing bio-inspired swimming robots. It provides a scientific framework for optimizing the shape of the robot to achieve a particular performance objective such as minimizing power consumption or achieving maximum swimming velocity across different hydrodynamic regimes,” said Fotis Sotiropoulos who led the study. Such super-aquatic robots could be built to retrieve samples from toxic waste pools or ocean depths.

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