New day, new girl!
Unlike in the first video, this rainbow trout is swimming at the top speed used in the experiment, 2.5 times her own body length per second! You can see just how fast she’s beating her tail, and you may also notice she isn’t really opening and closing her mouth here! She’s relying on ram ventilation to get enough oxygen from the water, since she must focus her energy on swimming against the strong current and opening and closing her mouth uses some of that energy. Not to worry, after each period of exertion she got a period of rest about the same size.
Something that I’ve noticed is that these rainbow trouts have a preferred location in the respirometer chamber. The rainbow trout in the first video was at the very front, some preferred to be at the end with their tail almost touching the net, one girl kept her position precisely in the middle of the chamber the whole time. They also seem to have preferences if they want to swim higher or lower! I suspect it may also be how they would position themselves in a school or the tank they inhabit.
Something pretty cool I just recently realised is — we can’t legally test animals to exhaustion (thank cod), so even while swimming 2.5 times her own body weight a second for three and a half minutes (twice), the rainbow trout was perhaps more tired but never actually exhausted! I do feel that’s quite remarkable, given how the rainbow trout we tested were rather young and never lived in an actually high-flow environment like a stream. Still, they could keep it up! Shows you just how well equipped salmonids are for swimming.
