Norwegian topknot
Otolith description
Otolith shape is oval. The sulcus runs over more than half the length of the otolith. The sulcus is open at the ostium, narrow and not very deep. Ostium and cauda are well distinguishable and separated by narrowing of the sulcus. The ostium is longer and wider than the cauda. The ostium is long and becomes wider from the centre of the otolith to the margin. The surface of the inside and outside is smooth. The margins are rounded with a round pointed end at the ventral, dorsal and posterior side. The rostrum of the otolith is rounded and a small rounded antirostrum is visible. The inside of the otolith is convex and the outside is flat. The otolith is thick. Norwegian topknot is a small fish and otolith length does not exceed 2.5 mm.
Norwegian topknot otoliths are difficult to distinguish from lemon sole Microstomus kitt. The sulcus of lemon sole is longer and deeper and ostium and cauda are better developed than in norwegian topknot otoliths. The ostium in norwegian topknot is wider at the margin than in lemon sole otoliths. Also the otolith length-width ratio in norwegian topknot is smaller than in lemon sole.
The otoliths are more rounder and the sulcus becomes less visible when otoliths are eroded. The antirostrum of the otoliths remains visible.
Fish length and distribution
Norwegian topknot can grow up to 12 cm. Norwegian topknot is a small bottom-living flatfish (PHRYNORV.TIF) that is found among rocks and rough grounds at depths up to 50 m (Wheeler, 1978). It spawns from April to July (Witte et al., 1991, Muus et al., 1999).
Norwegian topknot can be found on the continental shelf of the Eastern Atlantic and on the Scottish, Danish and Norwegian coast in the North Sea.
Sample origin
North Sea.