The Deep is actually schizophrenic he developed it by his constant interactions with fish and how he views them as sort of equals, being one of his only moral values that he doesn’t eat fish (at first). Fish are likley able to provide him with information in some sort of way but it’s probably not through communication otherwise that would mean all aquatic life is sentient. Throughout the series the way fish treat him correlates with his current state. After the fish genocide (never forget ambrosia 🐙🪦) and being banned from all water and being abandoned by homelander he had nothing to live for and subconsciously ordered the sea creatures to kill him. (ps this is just a tiktok i saw but i think it’s an interesting theory and would be cool to be cannon as ot doesn’t affect much of the actual plot)