Perca is the genus of fish referred to as perch or yellow perch, a group of freshwater fish belonging to the family Percidae. Perch have "rough" or ctenoid scales. When looking through a microscope, the scale look like a plate with growth rings and spikes on the top edges. Externally the anatomy of perch is simple enough. On the dorsal side of the fish, there consists a upper maxilla and lower mandible for the mouth, a pair of nostrils, and two lidless eyes. On the posterior sides are the operculum, which are used to protect the gills. Also there is the lateral line system which is sensitive to vibrations in the water. They have a pair of pectoral and pelvic fins. On the anterior end of the fish, there are two dorsal fins. The first one is spiny and the second is soft. There is also an anal fin, which is also considered spiny, and a caudal fin. Also there is a cloacal opening right behind the anal fin.