I did quite a bit of research into doing a cannabis aquaponics grow. What I learned is that the water from fish tanks does not have the right nutrient ratios for good cannabis growth. Seemed to me that there is way too much N and very little of any other nutrients. If you cannot grow cannabis in an aquaponics setup, that pretty much means that you should not be using fish water to water your plants.
However things like lettuce and other greens do very well.