To be honest: Only Unity Standard Shader and Material with some Emission.
Post Processing Did the Magic here.
Just rated your game. Here is what I think: Cool and Relaxing experience. missed a bit dynamic here. because although I dived deeper it felt kind of repetetive. I don't know if there is an specific end, always died before I could experience that. But what would be cool: If you add some layers of Depth: In the beginning only small and cute fishes. And the deeper you get the darker the see becomes. And more dangerous, bigger and faster fish appear.
Still: I enjoyed playing it. Keep in jamming :)