> To extend this conclusion from the dead fish experiments to mechanical devices, and to demonstrate the applicability of these results in an engineering context, we also show that a flexibly mounted two-dimensional rigid foil, through fluid-induced motion only, is capable of producing net thrust using a negative mechanical power input, i.e. all the required mechanical power is extracted from the flow.

from the paper, which was published in 2006. and re a downstream comment, they euthanized the fish with a bath of anaesthetic, also in the paper.

I didn't see that part. If it works with a foil fish then it is possible to have net forward thrust only by extracting the energy from the flow of the water.

Where does the energy for muscle flexing come from in a dead fish? Without a heart circulating blood (and ATP), My expectation would be that the muscles would quickly run out of power.

If you do that test where you apply electricity to a dead frog's leg to get it to kick, it will only work a few times before it's out of juice.

That swimming video is pretty short. Kicking a few times is all that you need.

The energy comes from stores in the cells and when those stores are depeleated the cell will replenish the stores by digesting itself.

"months after death"? Can you share a citation here?

I misremembered, after a quick Google it's days not months.

I reckon efficient swimming is too complex a process for spontaneous innervation to be responsible.

A fresh dead and pithed fish might flop, and might even flop several times in a row but that's about as far as it goes.

E.g. Just a change in temperature can make an efficiently swimming fish's red muscles’ duty cycles so maladaptive they are doing negative work, swimming requires really specific firing patterns.

Also consider — chances are they were moving an anesthetised fish into the experimental apparatus without realising it overdosed, in which case innervation would have been negligible.