The coamsh has possibly more names than any other fish except salmon. Depending where you are you will hear it called coalfish, saithe, lythe or billet. To the fishmonger it is coley and if you fish on the North Atlantic coast of America you find it goes by the name of pollock.
It is not just the names which tend to be confusing with the coalfish. Sometimes its identification causes problems too. The reason is that it is a close relative of our pollack and looks very similar to it.
Both coalfish and pollack are members of the cod family and have the typical three dorsal fins and two anal fins. They are both a dark greeny-brown above and lighter on the belly, and have relatively large eyes.
The two species may be similar in appearance, but if you look closely there are several clear-cut features which identify the coalfish for certain.
The jaws are of equal length but in big specimens the lower jaw is slightly longer than the upper – in pollack the lower jaw is much longer.
The lateral line is straight and creamy coloured, running directly from the gill covers to the tail – in pollack it is dark and strongly curved over the pectoral fin. The sides are dull and silvery and the transition to the back colouring is sharp – in pollack the sides are golden and the colouring merges with the back.
Coalfish are mid-water predators and typical shoaling fish, often found around reefs, wrecks or rocky ground, or swimming above the kelp forest.
Large fish tend to live in big schools in open water, although you might get a big solitary fish inside a wreck or gully.
In contrast the young, during their first two years of life, live in very shallow water among rocks and weeds. In northern Britain young coalfish even inhabit shore pools – but they are small fish, from 10-15cm (4-6in) in length. These young fish eat small crustaceans and other young fish, but as they grow they increasingly become fish-eaters. Sandeels, sprats, herring, poor cod and bib all go to feed the coalfish. Many of these food fish have been heavily commercially overfished – something that will affect future coalie numbers.
The coalfish becomes sexually mature at five to ten years old and spawns from January to April in depths of 100-180m (330-600ft). It spawns in places of high salinity and a temperature of 6-8°C (43-47°F).
The most important breeding areas are in the northern North Sea, off Norway and the Faroes. Small numbers breed off our coasts.
The eggs and larvae float in the upper 27m (90ft) of the sea, and the young fish are carried inshore by currents — into nursery ground waters of a few feet deep.
A European cold water species, the coalfish ranges from the Arctic southwards to the British Isles.
They are a favourite quarry of boat anglers. In winter, specimen hunters head for the deep-water wrecks off our coasts which hold hundreds of big coalfish – they can put up quite a fight on sporting tackle.
Commercial fishermen also target the coalie, catching them mainly in open water of 40-180m (130-600ft), by net, trawl and long line.