North Atlantic blue fish (large mackerel) are nothing but overgrown piranhas. I was wind surfing in the ocean late in the fall and about a half mile off the beach, before I realized what was happening, I sailed directly over a huge school of them, about a hundred yards long and the same across. They were in a feeding frenzy following a school of bait fish. The water was boiling and was red from the blood. These fish have razor sharp teeth and they were gnashing at anything that moved. My biggest fear was falling off the board in the middle of this feeding frenzy. Luckily I got pass them and I was safe, but man was my heart pounding. They would have picked my flesh off down to the bone. Have to admit, this was one of the few times I was really scared!
Good luck with the pets!