What does today's post have to do with genealogy? Nothing and maybe everything. Your ancestors and mine (especially your Scandinavian ancestors of which I have none :-) ate whale blubber and whale meat and tons of cod fish. THEY knew the difference.
Whales have lungs, their tail goes up/down and is attached horizontally, and they give birth to live young and nurse them, and has smooth, rubber-like skin.
Fish have gills, their tail is vertical and goes side-to-side, they lay eggs in water and swim away, and they have rough scales.
Now you know. Pop a quiz to your fishing grandsons!