Room for the fast and slow in fish schools

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Scientists studying the dynamics of schools of fish have discovered that the leading fish in the school are generally the fittest, while those at the back are weaker.

However, these weaker fish benefit from the reduced drag created by the slipstream of their stronger school mates and as a result need to expend less energy compared to the fit ones to keep up.

Despite this, the lead fish are not knowingly helping their less speedy cohorts, instead they are getting the best choice of food while the slow coaches are only getting the leftovers.

The research team filmed schools of eight juvenile Golden grey mullet (Liza aurata) in a swim tunnel to see how each fish in the school ordered itself against the others. An estimate of each fishes' metabolic rate was taken by recording the number of strokes of their tails in comparison to the speed at which oxygen levels in the water dropped.

The researchers believe that while swimming at 30cm per second the fish at the rear of the school were using 12% less energy in comparison to the leaders. The study also has interesting implications for the make up of schools in the wild, with speculation that fish of similar fitness levels are more likely to school together as holding formation with much faster or slower fish would be energy inefficient.

Fish school to help them evade predation as well as to boost their chances of finding food – safety in numbers as well as more eyes to spot danger and potential food. However, until this study it was believed that all members of the group benefited equally in food terms wherever they swam.

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