Okay, I'm uploading it to Dropbox now but it will take a while. In the meantime, I'll provide some more info. It is a singleplayer world, and I currently play it in 1.14.1 (Not 1.14pre-4, I didn't realize that, whoops), although it was actually created around 1.12 I believe. The reef and oceans I'm exploring have been loaded in since the update aquatic, and therefore are new (but because it's a somewhat old save any pre-1.13 loaded chunks don't have tropical fish). I have seen many tropical fish in the one particular reef I've been exploring, and the areas around it, but now I find none. I have a lot of fish at my base, and I'm thinking that having this many fish in the game might be prohibiting fish from spawning in the wild, but I've really got no clue.
https://www.dropbox.com/sh/ijoojgg6vkre5ju/AAB5-EVaoeRBPwut-M3zMRVha?dl=0
Here's a Dropbox link to my world's save file