I would like to add Hordy (sometimes spelled Hody) might be a reference to Vice Admiral Horthy Miklos. He was the leader of Hungary during world war 2 and fought in the Autro-Hungarian Navy during world war 1.
While the real life Horthy wasn't really racist, I can imagine that a Japanese Author would look at an Admiral who allied with Hitler as a convenient name-reference for the leader of a racist Fishman army. Tho it is just a slight name reference, nothing more.
I have written a book and know the pain of inventing names, cuz it needs to sound real and memorable and not just some gibberish. Often times when I need a new name I google a real life person who has a certain trait or characteristic connected with the fictional character (successful businessman, explorer, murderer, general, pacifist, poet, you name it) and then just edit the name slightly to make it a bit different.
I'm sure other Authors do that too and as we can see above (like Alvida) the author of OP does it as well.
I am sure there are many character names, places etc. that are slight references to real life people and places.
Water 7 is obviously a reference to Venice, Impel down is Alcatraz, Head Warden Magelan is a reference to the explorer of the same name etc. etc.