The world’s biggest flatfish

Whilst black halibut only grows to an average length of one metre – males about 80 cm and females 1.20 cm – the record for Atlantic halibut is 3 m and 320 kg. Atlantic halibut is thus considered to be the biggest representative of the flatfish species worldwide. The two species also differ in colour, although Atlantic halibut is not really white: but the grey-brown darkly marbled shade on the eye side is visibly paler than is the case with black halibut. The differences on the blind side are even more marked: whilst Atlantic halibut– like nearly all flatfishes – is pure white, black halibut has the same colouring here as on the upper side.

One difference that could be of particular significance – and not only for gourmets – is the difference in the culinary attributes of the two flatfishes. Flavour and consistency of black halibut are probably sufficiently known for hot smoked pieces of black halibut are part of the standard range at northern European fishmongers’. Its snow white flesh is short-fibred and very soft. This is due to the high fat content which over the course of the year rises to above 20% and even at spawning time when the fishes eat less and become haggard rarely falls below 10%. These product attributes set certain limits on the possible usages of black halibut in the kitchen. The fish is particularly suited to grilling, baking and frying. In the north of Scandinavia and on Greenland the fillets are also often dried or preserved through salting. Salted halibut roe is considered a particular delicacy.

Atlantic halibut – an expensive delicacy

The flesh of the Atlantic halibut is also white but, in contrast to that of black halibut, is much firmer and has a considerably lower fat content with average fat content fluctuating around only 6%. Sometimes it can sink so low that the fillet is almost too dry. If a fishmonger or good restaurant offers Atlantic halibut it would be a shame to miss the opportunity to enjoy this fish which is one of the best the northern oceans have to offer… something which is also to be seen in the price, for Atlantic halibut costs about twice as much as black halibut. Examination of the catch statistics soon explains this price difference. The global average annual catch of black halibut is 120,000 t (FAO, 2010), of Atlantic halibut only 5,600 t. Demand for Atlantic halibut is high, supply limited, and the price accordingly attractive. It would be hard to conceive of better preconditions for producing a fish in aquaculture! And so for a lot of years Norway, Iceland and other countries invested considerable sums in the development of farming techniques for Atlantic halibut. The bottleneck so far was above all the production of sufficient juveniles to enable regular stocking of the net cages in the sea. Production has stagnated at about 1,800 tonnes for the three years to 2010 with Norway responsible for almost all the tonnage. Although Atlantic halibut will presumably never achieve the market success of salmon, if it picks up aquaculture might in this case, too, make a decisive contribution towards giving this excellent fish a firmer place on restaurant menus.

But the Greenland or black halibut is also a valuable food and on account of its high fat content very recommendable. Its fat is highly rich in polyunsaturated Omega 3 fatty acids which are said to have numerous health giving benefits – a fountain of youth for the human organism, so to speak. And black halibut also contains minerals, trace elements and essential amino acids that our bodies cannot produce themselves. One hundred grams of halibut cover the higher daily needs of vitamin D in growing children and pregnant women.

Black halibut is a voracious feeder

These “inner values” are no accident, either, for black halibut is a fish that loves the cold and prefers to live in the icy water of the Arctic Ocean to the north of 60° latitude, at depths of between 500 and 1,000 metres where temperatures are constantly around 4°C. The greedy predator swallows just about everything that it can get the better of: small-sized skate, cod and other fishes, squid and crustaceans. Northern prawn (Pandalus borealis) is a particular favourite. The broad deeply cloven mouth has numerous pointed spear-like teeth, which in the upper jaw are arranged in two rows behind each other. Fishermen often have interesting tales to tell of the voracity of these flatfishes. Sometimes they even seem to follow the fishing vessels and devour everything that is thrown overboard from the ship’s kitchen: chop bones, poultry remains and other kitchen waste have been found in the stomachs of these halibut.

Tagging experiments have confirmed that black halibut undertakes extensive migrations in the North Atlantic when moving between their winter habitat, and their grazing and spawning grounds. In the course of a year they cover several hundred kilometres in the process. The spawning grounds off the Norwegian coast are between Vesterålen and Bear Island on the slope of the continental shelf. The fishes migrate to this region during spawning time which lasts from March to June. In the dark depths of about 1,000 m the females eject several hundred thousand eggs which are subsequently fertilized by the males. The eggs are a good 3 mm in size, float in the water and drift with the currents. When the tiny larvae hatch they are only 6 to 7 mm long. At that time they hardly resemble their parents at all for the translucent body is absolutely symmetrical. It is only when they have reached a length of 25 mm that the left eye begins to move to the right side of the body and the juveniles take on the typical appearance of a flatfish. In spite of their enormous appetites the fishes grow only slowly. After 6 to 8 years they measure about 55 cm and have attained sexual maturity. The oldest proven age of black halibut is about 30 years.

Manfred Klinkhardt

However, hardly any fish reaches that age today because pressure from fisheries has increased. Icelandic and Norwegian fishermen, in particular, go after halibut with trawls and longlines. The catch is mostly frozen immediately on board for the fat-rich fish spoils quickly, particularly at higher temperatures.

MK