It is mostly just the nautilus, however the sturgeon, coelacanth, and alligator gar all do this as well.

I'm having issues with fish spawning and breeding to an extreme, despite both being disabled in the config (and any other config that I can find that may affect mob spawns), and having an automated command run every 10 mins that kills all four creatures followed by a dropped item wipe. The nautilus spawn in groups of 5 or so, and have eggs just pouring out of them non-stop. If I don't send in a mob wipe (or at least an item wipe), going near them can and will crash my server in under a minute, and often item wipes don't even save it from crashing in time due to how quickly the eggs respawn. It had gotten so bad once before I had to load in the world with MCEdit to delete all the fish in an area to stop the crashing.

I've even tried a fresh world (and just copied structures over using Litematica), yet it still continues. Maybe it's a sudden mod conflict? I don't remember any mods updating right when this started happening, so I'm not 100%.

Example with the sturgeon/coels (after a wipe via MCEdit). The eggs are still pouring out.

Same general area in MCEdit

Selected some of it

After analyzing that selected section

Any ideas?