This bug was reported last year but it was never fixed. I have several fish tanks, one for each type of fish, and the salmon in my salmon fish tank aren't moving freely like all the other fish. They just stay in one spot or start spinning in circles extremely fast. They occasionally move to other spots but it takes a long time for them to do so and it never happens when I'm looking at them. I don't believe this is related to the depth of the water because I also have a small pond in my world with salmon in them and the pond has a smaller water depth than my fish tank. Also, I noticed this only happens when my fish tank has blocks above it. If I remove the blocks above the fish tank, they behave normally (which is why they behave normally in my pond).