No fish spawn cap/Constantly filling space of empty spawn points

In a bug report I mentioned before, I said that squids spawned in areas like rivers, which was odd. I used a couple of commands that simply teleported them away so they wouldn't look as if they spawned there. That's when I noticed a strange bug

A lot of salmon started spawning in the rivers, and I noticed that it only happened when the squids weren't there. Do their spawn caps rely on other mobs or something or do they even have a spawn cap at all?

As you can see in the image below, a lot of salmon have appeared while I'm teleporting the squids away