Perca fluviatilis


Otolith description
The general shape of the otolith is ovally pointed. The sulcus runs straight over of the length of the otolith, with the cauda slightly pointing down. The sulcus is clearly visible and open at the ostium. Ostium and cauda are separated by a slight narrowing of the sulcus. The ostium is slightly wider and shorter than the cauda, but cauda also widens slightly at its end. The surface of the inside and outside is smooth. The dorsal and posterior margins are strongly lobate or jagged. The lobation is variable but in larger specimens the otoliths are generally more jagged. The ventral margin is straight or slightly rounded. The rostrum is well-developed and pointed, while the antirostrum is small and also pointed. There is an indentation between the rostrum and antirostrum. The inside is convex and the outside concave. The otolith is thin.
Otoliths of perch are similar to zander Stizostedion lucioperca, pike Esox lucius and clupeidae otoliths. Clupeidae are all marine fish, so the origin of the material may provide a clue for separating perch from clupeidae. The otolith length-width ratio of zander is larger than of perch otoliths. The rostrum of zander is not as well-developed as in perch. The sulcus of zander is straight and not pointing down at the posterior and the posterior margin is pointed instead of round and jagged as in perch otoliths. Zander can also be separated from perch by other skeletal remains. Zander often leaves jaws with large tooth in diet samples; perch leaves spiny preoperculae and scales shaped like baseball gloves. Pike otoliths are strongly concave at the outside, more so than perch or zander. The sulcus of pike is wider and the rostrum is larger and more pointed.
When eroded the sulcus becomes indistinct. The rostrum is still visible but rounded and the margins are smoothed. Often the rostrum is missing.
Otoliths of juveniles are rounder. The sulcus is straight and already slightly pointing down at the posterior. The rostrum is not well-developed and the margins are irregular but not lobate or jagged. Otoliths of juvenile perch resemble otoliths of ruffe Gymnocephalus cernuus. The sulcus of ruffe otoliths is wider and straight and the posterior end of the sulcus is not pointing down. Otoliths of ruffe are thicker and more lobate on the margins than are small perch otoliths.

Perch otoliths in diet samples are usually accompanied by hard, remarkably spiny skeletal parts, such as the preoperculum and by scales that have the shape of a baseball glove. These parts often help to separated perch from fish with similar otoliths.

Fish length and distribution
Perch can grow up to 60 cm. Perch is a common fresh water fish, living in schools when small and becoming solitary when larger. They are found in rivers and ponds with a slow current. Perch prefer open water but are also found in vegetated water bodies. It is also found in the brackish waters of the Baltic. Spawning takes place in April and May (Wheeler, 1978, Nijssen and De Groot, 1987).
Perch is very common and found throughout Europe and in the brackish waters of the Baltic.

Sample origin
Northern part of the Netherlands and Lake IJssel.