Minecraft 1.13, Minecraft 18w32a
If there are at least 16 fish spawned from buckets anywhere in loaded chunks (that might be the spawn chunks, chunks loaded via /chunk, or chunks that players currently are in), no aquatic mobs (fish, dolphins, and squid) will spawn anywhere.
- Create a new superflat world (I chose "Redstone Ready") and change it so that it has biome minecraft:ocean
- Create a big aquarium at spawn
- Drop 16 salmon from buckets in there
- Teleport to somewhere far away, for example
- Check that all salmon still are there
- Create a big aquarium there as well
- Notice that no mobs spawn there whatsoever
- Notice that suddenly, there are many mobs spawning in that aquarium
Change the aquatic mob cap so that fish spawned from buckets no longer affect it.
As stated tropical fish and pufferfish are not spawning whatsoever in my main world. I created another world to see if they would spawn there and they spawned just fine. I have spent hours upon hours in my main world and I don't want to have to restart. Is there any way to fix this? I don't know if it's a factor, but I had to travel a fair distance from my spawn point to find warm ocean.