Bite most definitely, heater's been shut off for a month. Hard to say what bit er, have a 15" clown knife, 12" florida gar, 10" rope fish, 10" black ghost knife, 8" ornate bicher, 8" glass knife, 6" bala shark... The glass knife seems to be the most aggressive of the bunch (surprisingly) but not sure it could make a mark that big.. Haven't seen a single thing in the tank so much as inquire about the motoro being food, so I'm assuming it must have startled something.. Also heard rays are pretty much tanks, and heal pretty quickly from flesh wounds like this.