Natures wonders: fish schools save energy (Introduction)

by David Turell , Monday, December 18, 2023, 16:17 (131 days ago) @ David Turell

Swimming together does save energy:

https://www.newscientist.com/article/2407338-swimming-together-lets-fish-move-faster-wh...

Swimming in schools has massive energy-saving benefits for fish. A study in “water tunnels” has found that fish use half as much energy swimming at high speeds if they are in a school rather than alone, and they also recover in nearly half the time.

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It has long been thought that swimming in schools reduces energy use in addition to various other benefits such as protection from predators. But measuring energy use in free-swimming fish is tricky, not least because as fish swim faster they can no longer generate enough energy using only the oxygen they take in via their gills – aerobic respiration – and start using energy reserves stored in muscles – anaerobic respiration.

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Crucially, the pair kept measuring oxygen consumption for at least 19 hours after the fish swam at a certain speed. The more energy reserves fish use for anaerobic respiration, the more oxygen they consume to replenish those reserves after exercise.

Previous studies have measured oxygen consumption only during swimming, which reflects only aerobic energy use. Post-exercise oxygen consumption provides a measure of anaerobic respiration as well, allowing the total energy used during swimming to be estimated.

Zhang and Lauder found that at low speeds – between 0 and 3 body lengths per second – there was little difference in energy use between shoals and single fish. But at higher speeds fish in schools used a lot less energy.

At 7 body lengths per second, for instance, on average each fish in a school used 53 per cent less energy than solitary fish. At this speed the schooling fish were still getting 50 per cent of their energy from aerobic respiration, whereas the solitary fish were getting just 20 per cent, relying on anaerobic sources for the other 80 per cent.

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“I think they did a great job,” says Keith Tierney at the University of Alberta in Canada, whose team has measured lactate production in fish as an alternative way of estimating anaerobic respiration.

Overall the results are in line with his expectations. But what is surprising, says Tierney, is that Zhang and Lauder found that fish in schools beat their tails at the same frequencies as solitary fish swimming at the same speeds, but use half as much energy per beat. “Very cool.”

Comment: we see what they discovered, but no explanation as to why. My guess is a 'drafting' effect as in racing cars, which does save fuel. The lead car parts the air and the following car enjoys the vacuum in front of it. The fish must have easily recognized the advantage, so I think this is a learned instinct.