Perca fluviatilis

The colour of the perch depends on the habitat in which they live. In shallow areas where light penetration is good, they tend to be darkly coloured whereas in poorly lit areas without vegetation they are lightly coloured. Carotenoids, derived from crustaceans in the diet, sometimes make them deeply reddish-yellow. The dorsal surface is usually bright green to olive which extends down the sides in seven tapering bars. The sides are yellow to yellow-green and the ventral surface grey to white. The eyes are green to yellow, as are the caudal and dorsal fins. The first spine of the dorsal fin is often black and the membrane between spines one and two and that between the last four or five spines is also blackish. The pectoral fins are amber and transparent whereas the pelvic and anal fins are silver-white to yellow and opaque. Some perch have been observed to be entirely black. Male perch have thicker skin than females for most of the year (Lindesjšš, 1994). Regardless of sex, the epidermis is thickest in the prespawning period whereas the dermis is thickest after spawning. The body feels rough to the touch as a result of low mucus production and the presence of ctenoid scales. There are 51-61 scales along the lateral line.