Unlike all other fish types, Pufferfish do not spawn in all deep variants of the oceans they spawn in.
Specifically, they do not spawn in Deep Warm Ocean
MC-217379
Pufferfish don't spawn in deep warm oceans
Resolved
Fixed
8
Confirmed
Mob spawning
1.16.5, 1.17.1 Pre-release 2, 1.17.1, 21w39a
21w43a
Retrieved
Confirmed in 1.17.1. Might get fixed in 1.18, because the Deep Warm Ocean generates naturally in 1.18 ES1. (of course if the change stays until official 1.18 snapshots)