I feed my rays frozen tilapia fillet daily. no problems at all.
Freezing things doesnt kill bacteria, it simply slows their growth. If you dont let the food thaw for more than 20 minutes, then the bacteria present on the food will not have enough time to mulitply enough to become harmfull enough to kill the fish. Only cooking it to a high enough temperature will kill harmful bacteria.
Chances are, if you are purchasing tilapia that is meant for human consumption, then there is no bacteria or anything harmfull on it. The food industry has extremly vigourous standerds when it comes to meat and fish. If there is bacteria present on the fish, then it will be at a "acceptable" level, and have a very low bacteria count.
Buy fish that is meant for human consumption, keep it frozen and dont let it thaw longer than 20mins and you'll be good to go.