[allmendream]

Yes, and the selective advantage of flying HAS modified a swimming fish into a “flying” fish.

Do you think that using selective breeding I could not make a different type of fish “fly”?

It is hardly a major adaptation. One might have a rougher time turning a wolf into a herding dog, a hunting dog, a retrieving dog or a guard dog; or all of the above - and humans did that in short order.

It is hard to deny the sheer power of selection of variation that we have demonstrated just upon our own domestic stock.

Darwin's model accurately predicts reality. Selection acts upon a population to either select for or against particular variations, resulting in a change in the population.

[valkyry1]

it is conceivable that flying-fish, which now glide far through the air, slightly rising and turning by the aid of their fluttering fins, might have been modified into perfectly winged animal

Once again you re-state and miss-characterize what was said so you have something you can answer.

The flying fish was and is a gliding fish. It never became a perfectly winged animal capable of powered flight such as a bird as Darwin speculated using his model.