Hello! Your answer is A and B.
These would be controlled variables. Controlled variables are parts of the experiment which are kept the same to make sure they do not interfere with the testing of another variable. For example, if you were testing the effects of sunlight on plant growth, you would want to make sure you were using the same plants (a controlled variable), same amount of water (another cv), etc.
Making sure all the aquariums used are the same size would be a controlled variable as it directly involves the fish that are used in the experiment, and can affect their behavior. It is not directly stated what is being tested here, but it most likely will affect the results. Giving the fish the same amount of food is also a controlled variable, for the same reasons.
However, taking notes about the color of the fish is important (depending on what is being tested), but it is not a controlled variable. It is not something which will directly affect the results of the experiment. It may affect the results you gather, however it will not alter the actual ones.
Hope this helps!