Hmm, my wife likes to swim, I better start calling her my fish.
Whales need to take breaths on the surface, unlike fish, which can stay underwater basically indefinitely. Without that difference, whaling would be a lot more complicated, if not outright impossible, especially in the 19th century - you just can't catch a huge solitary animal in an ocean on purpose if it doesn't have to surface from time to time. Or only with sheer luck.
Even the ancient whalers were aware of the fact that whales need to breathe, and thus, at the very least, could say "well, these are some rather special fish, you know".
Whales need to take breaths on the surface, unlike fish, which can stay underwater basically indefinitely. Without that difference, whaling would be a lot more complicated, if not outright impossible, especially in the 19th century - you just can't catch a huge solitary animal in an ocean on purpose if it doesn't have to surface from time to time. Or only with sheer luck.
Even the ancient whalers were aware of the fact that whales need to breathe, and thus, at the very least, could say "well, these are some rather special fish, you know".