Free As a Breeze...Wasteful Swimmers, Though, If You Please

Running on a treadmill in the gym isn't quite the real thing, and now it turns out that fish...bass, in particular...may have the same problem. That was the thinking of David Ellerby, from Wellesley College, USA.

His concern was that experiments in flow tunnels (the fish equivalent of treadmills) had suggested that fish naturally prefer to swim at a speed that consumes the least energy.

According to Ellerby, "Almost all measurements of fish-swimming costs are made at constant speeds imposed by the researchers, not those preferred by the fish. Although this is valuable information, we know very little about how the lab data actually relate to swimming behavior in the field."

As a result, Ellerby and two undergraduate students, Angela Han and Caroline Berlin, decided to get out of the lab and go swimming with free largemouth bass in Lake Waban to find out how realistic lab-based studies were. They devised an impromptu stereo-camera system by strapping a pair of GoPro cameras to a camera head, donned their snorkels, and got in the water.

Back in the lab, the trio estimated the length of each bass from the video and then measured each one's speed, the directness of the path each had taken, and how fast each had beat its tail. However, when the team compared the speeds that the fish had been swimming in the lake, with the most economical speeds that had been recorded in a flow tunnel in the lab, they were astonished by the findings. The majority of the free fish were swimming at slower, less economical speeds than the optimal speeds that had been recorded in a flow tunnel.

Wondering why the free fish might have opted for a more profligate (recklessly wasteful) swimming speed, Ellerby suggested the fish may have to accept a more costly slower speed to increase their chances of snapping up tasty morsels as they move around. Alternatively, he noted that it's possible the fish that were swimming in the flow tunnel when their metabolic rates were measured were not behaving as naturally as the freely swimming lake fish.

Either way, Ellerby warned that the behavior of fish in the real world may be subtly different from that of fish pounding a metaphorical treadmill.

I suggest, however, that maybe the difference is just a reflection that free fish...those in the real world...like to dream a little about swimming "up a lazy river by the old mill run, the lazy, lazy river in the noon day sun," as in the lyrics of that old 1930s song...pardon me for being a bit facetious.

While researching this info, I also happened across some other biological-study data that indicated bass are capable of swimming up to 2.5 times their body length per second. This means that a small fish can swim about 2 miles per hour, while a 20-inch fish may swim in spurts of up to 12 miles per hour.