Bull-rout
Otolith description
The general shape of the otolith is ovally pointed. The sulcus runs almost straight over of the length of the otolith. The sulcus is deep and open at the ostium. Ostium and cauda are distinguishable and separated by a narrowing of the sulcus. The ostium is wider than the cauda. The surface of the inside and outside is smooth. The ventral margin is straight or slightly rounded, but smooth. The dorsal margin is rounded and slightly lobate. The rostrum is well developed and pointed, while the antirostrum is small and rounded. The anterior margin is indented between the rostrum and antirostrum. The posterior margin is pointed. The inside is convex and the outside concave. The otolith is thick.
Otoliths of bull-rout are difficult to distinguish from other cottidae, such as sea scorpion Taurulus bubalis, and bullhead Cottus gobio. Otoliths of bull-rout are the largest of the three, otoliths >5 mm are always of bull-rout. The general shape of sea scorpion otoliths is more lanceolate. The sulcus is less developed than in bull-rout otoliths and is pointing down at the posterior. The ventral part of the otoliths of sea scorpion is thicker than the dorsal part. The rostrum of sea scorpion otoliths is rounder. Also the dorsal margin is round and not lobate as in bull-rout otoliths.
In bullhead otoliths the length-width ratio is larger than in bull-rout. The sulcus is less well developed and not deep. The antirostrum is less distinct than in bull-rout otoliths. The posterior end of the bullhead otoliths is more pointed compared to bull-rout otoliths (but the same pointed shape may be found in otoliths of small specimens of sea scorpion). Otoliths of bull-head are irregular on the outside instead of smooth. Note that bullheads are fresh water fish, so that origin of material may provide a clue for the identification.
When eroded the sulcus becomes indistinct. The rostrum and posterior end remain pointed. The dorsal margin is smoothed. Eroded otoliths are very similar to hooknose Agonus cataphractus. The sulcus of hooknose otoliths is wider compared to bull-rout. The length-width ratio in bull-rout is larger than in hooknose otoliths.
Otoliths of juvenile bull-rout are very different from otoliths of older fish. The general shape is two lobes separated by and indention at the ventral and dorsal side. The rostrum is indistinct and rounded as is the posterior end.
In samples sometimes the preoperculae of cottidae can be found. These can be useful for determining the species of cottidae. The preoperculum of bull-rout has two relatively short but straight spines which are pointing more upwards than backwards. Sea scorpion has one long slightly curved spine on the preoperculum. The spine is pointing more backwards than upwards. Since bull-rout becomes much longer than sea scorpion the spines in large bull-rout may be as long as in sea scorpion, but there will always be two spine visible on the preoperculum of bull-rout. Bullhead has only one not well-developed spine on the preoperculum.
Fish length and distribution
Bull-rout can grow up to 30 cm. Bull-rout is a bottom-living fish (MYOXSCOR.TIF) found in coastal waters on a wide range of bottoms, from sand to mud but also among rocks. It can also be found in brackish waters. It spawns from December to March and the eggs are deposited among rocks (Wheeler, 1978, Nijssen and De Groot, 1987, Witte et al., 1991, Knijn et al., 1993, Muus et al., 1999).
Bull-rout is a common fish found in the coastal waters of the NE Atlantic, North Sea and Baltic.
Sample origin
Fyke and Southern North Sea.