Use a fork or the tip of a knife to gently press into the thickest part of the fillet. If the fish flakes easily and the flesh is opaque, it's a good indication that the tilapia is cooked through. The flakes should separate easily and appear moist, not translucent or raw. The internal temperature of cooked tilapia should reach 145 degrees Fahrenheit (63 degrees Celsius) as recommended by the USDA. .