@Psychedelic_Zebra The reasons why tilapia are desirable have to do with how easy they are to grow and how unfishy they taste. They are very tolerant of extremely dirty conditions. So some fish farmers, in order to save money, grow their fish in very dirty water. Then, the last day or two before harvesting, they let them in clean water to clean out their systems. They also use antibiotics to keep the fish healthy.
Not every farmer does this, but you never know where your fish come from, nor how they were raised, and thus I, for one, never eat them. People who sell fish farm systems are not likely to tell you how these systems can be used—where farmers can cut corners. But a number of years ago, I did a study of aquaculture with the idea that it was something that inner city entrepreneurs could do. During the course of that study, I picked up that tidbit of information—I don’t remember where now. It was enough to put me off.