Identification:
Classic codfish shape, with three rounded dorsal and two anal fins. The
pelvic fins are small with the first ray extended, and are set under the gill
cover (ie the throat region), in front of the pectorals. The upper jaw extends
over the lower jaw, which has a well developed chin barbel. Medium sized eyes,
approximately the same as the length of the chin barbel.
Distinct white lateral line running from the gill slit above the pectoral
fin, to the base of the caudal or tail fin. The back tends to be a greenish to
sandy brown, and showing extensive mottling especially towards the lighter sides
and white belly. Dark brown colouration of the back and sides is not uncommon
especially for individuals who have resided in rocky inshore regions.
Breeding:
The Cod population comprises of a number of reasonably distinct stocks over
it's range. These include the Arcto-Norwegian, North Sea, Faroe, Iceland, East
Greenland, West Greenland, Newfoundland, and Labrador stocks. There would seem
to be little interchange between the stocks, although migrations to their
individual breeding grounds may involve distances of 200 miles or more.
Spawning occurs between January to April (March to April, is the peak
time), at a depth of 200m in specific spawning grounds at water temperatures of
between 4-6oC. Around the UK, the major ones are associated with the Middle to
Southern North Sea, the start of the Bristol Channel (north of Newquay), The
Irish Channel (both east and west of the Isle of Man), around Stornoway, and
east of Helmsdale.
Pre-spawning courtship involves fin displays, and male grunting, which
leads to pairing. The male is inverted underneath the female, whilst the pair
swim in circles during the spawning process. The eggs are planktonic and hatch
between 8 to 23 days with the larva being some 4mm in length.This planktonic
phase lasts some ten weeks, during which the young cod will increase it's body
weight by 40 times, and be about 2cm in length. The young cod move to the seabed
and their diet changes to small benthic crustaceans, such as isopods and small
crabs. They increase in size to 8cm in the first six months, 14 to 18cm by the
end of their first year, and some 25 to 35cm by the end of the second. This rate
of growth tends to be less in individuals occupying northerly grounds.Cod reach
maturity at about 50cm in length at about 3 to 4 years of age.
Habitat:
Varied, although often favouring rough ground especially inshore. Demersal
in depths of between 20 to 200m (80m Av.), although not uncommon to depths of
600m. Gregarious and forms schools, although shoaling tends to be a feature of
the spawning season.
Food:
Adult cod are active hunters, feeding on sandeels, whiting, haddock, small
cod, and squid, with a variety of benthic annelids, crustacea, and molluscs
supplementing their diets.
Range:
Throughout most of the UK waters, although generally seen as a winter fish
in the south.