What piranhas look like 1. Piranhas have short necks and hard skulls. The body is oval, flattened on the sides, grayish-green in color, dark green on the back, and bright red on the abdomen. Piranha, also known as piranha, is a species of fish found in the Amazon River in South America and is a species of piranha. 2. The neck of the piranha is short, the skull, especially the palatine bone is very hard, the body is oval, the side is flattened, and the tail fin is shaped. Edible fish. The body is oval, flattened laterally, and the caudal fin is also shaped. The body is grayish-green, the back is dark green, and the abdomen is bright red. With sharp teeth and well-developed jaws, it is known for its ferocity. 3. Piranhas are generally referred to as Serrasalmus nattereri, which has a flat body on the left and right, oval before and after, slightly forked tail fin, and a maximum body length of only about 32 cm. The body color varies greatly, and the dorsal side of the adult is blue-gray to grayish-black, and the belly has a silvery-gray sheen.