Note that Melville was well aware of the reasons that "whales aren't fish", and went over those in detail, then said he was going to call them fish anyway.
The whale=fish thing is also an old joke about catholics. Back when one could not eat meat on fridays, all sorts of water-living mamals were declared to be "fish" for purposes of eating. So a new world protestant author in the 1800s is pointing a critical finger at oldworld religion and science.
We have lost knowledge of such nuance, like rewatching MASH or Trek and missing the religious and racial messages that made them so controversial then but banal today.
In 1760, The Natural and Civil History of the French Dominions in North and South America did absolutely claim that there was some papal decree that otter tail was fish, and beaver was fish, and so on.
But... There's no actual Papal decree, bull, or otherwise in canon law that anyone can find. It's just a good story, not a true one.
Which doesnt matter. What maters is whether melville thought it to be true when he wrote the line. The joke/reference would have been understood by readers at the time regardless of whether it was factually true.
2010. Archibishop of New Orleans. Alligator is "fish". Whether or not the pope has an opinion, such things are not fiction.
Yes I agree. All the moreso because the word fish is very ancient and was used to mean any aquatic animal long before Linnaeus came along and decided to "well ackshully" the word.
This is a reach, but do you know where to find the essay I read about someone explaining to King David that a whale isn't a fish and the King laughs at him because his modern mammal explanations are useless and impractical compared to the ones he uses?
We have lost knowledge of such nuance, like rewatching MASH or Trek and missing the religious and racial messages that made them so controversial then but banal today.