Swimming in a school is like driving a car

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Schooling fish behave like cars in traffic, according to research published in a recent issue of the Proceedings of the National Academy of Sciences.

Studying groups of eastern mosquitofish (Gambusia holbrooki), James Herbert-Read and coauthors found that individual fish use simple traffic rules to maintain cohesiveness in a school, ignoring all but their nearest neighbours and changing speed based on their movements.

The authors filmed groups of two, four or eight mosquitofish in a square arena for five minutes, and studied the movements of individuals in each group using tracking software, which analysed the paths of each fish and how they responded to the position and orientation of their neighbours.  The researchers then used a technique called artificial neural networks to look for patterns in the data.

The authors found that each fish focused only on the movements of its nearest neighbours to maintain the synchronised swimming exhibited in schooling fish. The fish sped up if the neighbour was far in front or just immediately behind, and slowed down if the neighbour was far behind or too close in front. You can take a look at a video below:

This is not unlike driving a car in traffic. "When we're driving, we use similar sorts of rules: we decelerate when someone's in front of us, and accelerate if there's someone about to bump into you from behind," said senior author Herbert-Read.

"However, we also found some inconsistencies between the classical models of fish motion and our results. For example, we didn't find evidence that fish aligned specifically with their neighbour’s orientation. Instead, it looks like the group aligns in some other way, possibly through attraction and repulsion rules and by fish following individuals in front of themselves", he added.

For more information, see the paper: Herbert-Read, JE, A Perna, RP Mann, TM  Schaerf, DJT Sumpter and A Ward (2011) Inferring the rules of interaction of shoaling fish.  Proceedings of the National Academy of Sciences doi:10.1073/pnas.1109355108

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