The only warning I have seen against tilapia was about an additive sometimes added to packaged fish ad a preservative. This additive *might* have negative impact on garters. (If educated guess, not proven by testing.)

Some people don't have trust farm raised fish. They argue the diet fed is poor/ unhealthy and may conntain antibiotics and other substances absorbed from a crowded, unhealthy 'feedand lot' style life.
Others wont eat wild caught due to possible parasites and pollution contamination.
In *my* opinion, every food has its risks and benefits- you have to look at what is available in your region, at what cost, and find the best balance for yourself.