Fish from Seaquarium.

C&C Welcome, first time taking pictures of fish so advice and tips would be very useful. All pictures taken with my Tamron macro lens.

All look nice and sharp. One issue I can see is that everything is very back lit - that's always likely to happen in the tank. If you can get the fish when they're further away, that would help with some front lighting. Alternatively you could try lighting from the side with a torch, that should throw light on the subject, without causing reflections on the glass or blinding the fish with flash.