Cod
Otolith description
The shape of the otoliths is ovally pointed. When viewed from the side the otolith is strongly curved. The sulcus is well developed and wide. The sulcus is closed, but runs over almost the whole length of the otolith. The ostium and cauda are well developed and separated by a narrowing of the sulcus. The cauda is longer than the ostium. The surface of the inside is smooth, while the outside and margins are lobate. The rostrum is not well developed and round lobate. The antirostrum is indistinct. The posterior margin is pointed. The inside of the otolith is convex and the outside strongly concave. The otolith is thick. Otoliths of gadidae, except rockling otoliths, are all very large and mostly robust otoliths.
Cod otoliths are often hard to distinguish from other gadidae. Haddock Melanogrammus aeglefinus is more concave and less lobate at the outside. Whiting Merlangius merlangus and blue whiting Micromesistius poutassou are flatter and thinner and the otolith length-width ratio is larger than in cod otoliths; their posterior margins are more pointed. Otoliths of Trisopterus spp. are thicker and more lobate at the outside, while the otolith length-width ratio is smaller. Otoliths of Pollachius spp. are more concave on the outside. Pollachius otoliths are not only strongly curved from the anterior to the posterior but also from the ventral to the dorsal side. The sulcus of Pollachius otoliths is wider than in cod otoliths. Otoliths of tadpole-fish Raniceps raninus have a sulcus in which the ostium and cauda are completely separated. Tadpole-fish otoliths are flat and have one strongly protruding lobe on the outside of the otolith.
In eroded otoliths the sulcus is less clear and the margins are smoothed. The outside remains lobate.
On otoliths of juvenile cod the sulcus is indistinct. The margins and outside are already slightly lobate.
Fish length and distribution
Cod can grow up to 150 cm. Cod is a common demersal, schooling fish (GADUMORH.TIF) that is found in a variety of habitats and water depths. It is found in shallower water during winter, while the younger fish are always close to the shore. It spawns from January to April (Wheeler, 1978, Nijssen and De Groot, 1987, Witte et al., 1991, Knijn et al., 1993, Muus et al., 1999).
Cod is a very common fish found in the NE Atlantic, North Sea, Baltic and the arctic waters.
Sample origin
Fyke and Southern North Sea.