Flounder
Otolith description
Otolith shape is oval and rounded. The sulcus runs over more than half the length of the otolith and is closed. The sulcus is wider at the ostium than at the cauda. Ostium and cauda are clearly visible, deep and separated. Often the ostium is somewhat larger than the cauda. The surface of the otolith is smooth and somewhat irregular at the margins. The dorsal margin is straight, with a sharp point at the posterior end. The ventral, anterior and posterior margins are somewhat irregular. The rostrum of the otolith is pointed compared to other pleuronectidae. The inside of the otolith is convex. The outside of the otolith is concave at the posterior end and flat at the anterior. This is an important feature distinguishing this species from other pleuronectidae. Flounder otoliths are thin but thicker than plaice otoliths.
Eroded otoliths are often difficult to determine to species level. The sulcus of eroded otoliths widens and becomes less deep. When otoliths are eroded the sulcus remains longer visible in otoliths of flounder than in plaice otoliths. The margins of the otolith become smoother with progressed erosion.
Eroded otoliths of 0-group flatfish are not distinguishable with great certainty. Margins of small otoliths are rounder. In small otoliths the sulcus is not well developed but ostium and cauda are distinguishable and the ostium is wider than the cauda.
Fish length and distribution
Flounder can grow up to 60 cm. Flounder is a bottom-living flatfish (PLATFLES.TIF) found on sandy and muddy bottoms. It is an inshore living flatfish that penetrates into fresh waters. Juvenile fish are mainly found in the tidal zone, while adult fish are also found in deeper inshore waters (Wheeler, 1978, Witte et al., 1991, Knijn et al., 1993). Spawning occurs from February to May in salt water (Muus et al., 1999).
Flounder can be found in the NE Atlantic, North Sea and Baltic.
Sample origin
Fyke and western Wadden Sea. Larger fish were also caught in the southern North Sea.