Five-kilogram fishes within just a year

Although cobia (Rachycentron canadum) is still unknown to most consumers it is generally considered to be one of the most promising candidates for marine aquaculture. It is an excellent food fish. It grows extremely fast and is relatively robust. Its firm, white flesh has a nutty, buttery flavour and is rich in Omega 3 fatty acids. Everywhere, where cobia is already available on the market, demand is growing. Aquaculture production is rising.

 

A typical feature of cobia, in addition to its characteristic body shape, is the first dorsal fin with its 7 to 9 individual spines.

The fish industry and trade have long been searching for a white fish with a value-adding potential similar to that of salmon. Tilapia has so far been unable to assert itself on the European market as originally hoped, and after a very promising start pangasius has lost a lot of its initial attraction. Cobia is now the next fish species that is said to have the potential to become as great a success as salmon. And indeed, cobia has all the prerequisites that make a fish popular – and successful – with consumers. Its white flesh is relatively firm and hardly falls apart when heated, and the fillets can be prepared in almost any conceivable way. It has a pure, delicate flavour typical of marine fish, and added to these advantages is the fact that it does not produce any unpleasant fishy smell when cooked. With an average fat content of 18% in the fillet, cobia is on the same level as salmon and it even contains slightly more of the valuable Omega 3 fatty acids. In the face of these qualities it is not surprising that in some countries the fish is being traded as “tropical salmon” or “black salmon”.

Cobia, which also goes under the names black kingfish, crabeater, cubby yew, kingfish, lemonfish, runner, prodigal son, and sergeant fish is not, however, a salmonid but within the order Carangiformes is related to dolphinfish (Coryphaenidae), whose best-known species is probably mahi mahi (Coryphaena hippurus). Cobia fillet is in fact often compared to mahi mahi, although it would not be wrong to describe it as a kind of cross between swordfish and Chilean seabass. Although its culinary quality is coveted worldwide cobia was in the past rarely to be seen on restaurant menus. But that was due to the low availability of the fish for it is not targeted specifically by the fishing industry but is only landed as by-catch. According to FAO statistics less than 15,000 t of cobia are caught per year, particularly in Pakistan, Iran, the Philippines and Malaysia. The actual catch volume could be much higher, however, for the species is also a popular target of deep-sea sports fishing because the big fish (which can reach a length of 2 metres and a weight of 80 kg) put up a good fight on the hook. However, these catches are not correctly documented and do not appear in the catch statistics. Since cobia has been produced in aquaculture, however, availability has steadily increased. The fish is beginning to conquer the global market. Now it is time for consumers to decide whether it might become a success story like salmon. 

Deep-sea fish from warm oceans with worldwide distribution

Cobia is a pelagic marine fish which is to be found in the tropical and subtropical regions of the three oceans – with the exception of the East Pacific. The species is not faithful to any one area and follows far-reaching routes through the deep sea that are nevertheless predictable. The fishes usually swim in small groups of up to 100 specimens and keep close to flotsam or in the vicinity of other underwater structures such as drifting sea grass, buoys, turtles or boats, near harbour piers or oil and gas platforms. Occasionally schools of cobia are also to be found in shallower water along the coasts, in mangrove areas and estuaries.

Cobia has a cylindrical, almost shark-like body shape. Its head is broad and flattened, the eyes are relatively small, the lower jaw of the wide mouth protrudes slightly. Seven to nine short spines which can be folded against the body into corresponding grooves form the first dorsal fin. The second dorsal fin is much longer and its front spines protrude pennant-like in adult animals. The anal fin on the lower side of the body is shaped exactly the same but is somewhat shorter. In young fishes the tail fin is almost round like a plate but as the fishes grow older it takes on the shape of a crescent. The body surface looks relatively smooth because the small scales are embedded deeply into the firm, thick skin. Cobia is not spectacular in appearance but its colouring is striking. It has a dark brown back and a black colour band on the level of the eyes that extends from the nose to the tail fin which is flanked above and below by paler stripes. The characteristic colouring is often only found in juveniles, however, for at a later age it usually pales and is lost. Cobia is considered a carnivorous predator but studies of the stomach contents sooner suggest that the fish is an opportunist that hardly rejects anything that appears in its path. Its staple diet includes squid, crustaceans and smaller fishes of any kind but it will also sometimes follow sharks and other large marine predators to eat up the remains of their prey.

Cobia’s thick, leathery, tough skin and its hard bones demand a lot of strength and expertise during filleting.

Male cobia are mostly sexually mature already after one to two years, females after two to three years. At spawning time which, depending on the region, can be at different times of the year and vary in length (for example off North Carolina in May and June, in the Gulf of Mexico from April to September) the mature fishes gather in large swarms off the coasts. Individual groups probably also spawn in the open sea, however. Cobia has a protracted spawning season over the course of which it releases eggs about a dozen times at intervals of one to two weeks. The total fertility of the females lies between several hundred thousand and several million eggs, depending on size and age, but on average 75,000 eggs per kilogram of body weight. After they have swelled, fertilized cobia eggs reach a diameter of 1.2 to 1.4 mm and float freely in the water. The yolk sac larvae hatch already 24 to 36 hours after fertilization and are at this time only 2.5 mm in size and glass-like or transparent. Two days later the yolk reserves have been eaten and the mouths and eyes have developed sufficiently for the young to start feeding independently. At an age of 30 days the young fishes already resemble their parents with the striking longitudinal stripe standing out most. In this phase of life the juveniles often hide beneath floating carpets of algae and sea grass which offer protection from predators and at the same time a source of food.

 

Cobia is particularly well-suited for aquaculture

The start of cobia farming is mostly given as 1975. At that time US-American scientists collected fertilized eggs off the coast of North Carolina and after they hatched raised the fishes for a few months. By the end of this period they had come to a clear conclusion: due to the fast growth and excellent flesh quality cobia had all the prerequisites for successful aquaculture. Based on these studies research was then pursued further in the USA and Taiwan. One of the first focus areas of research was reproduction. At first the rearing of the tiny larvae presented huge problems and mortality was very high. Experienced fish farmers in Taiwan succeeded however in 1987 in closing the production cycle from the egg to the marketable fish. Since then the technology has been improved continuously and perfected in many details. Fry supply is still a bottleneck but it has stabilized significantly. Today it is basically possible to hatch cobia throughout the year. Around the turn of the millennium several countries began cobia farming almost simultaneously. Mostly for research purposes but partly also under commercial aspects.

There are several reasons why cobia is particularly well-suited to aquaculture. One of the most significant is its fast growth, for the fishes can reach a weight of five to six kilograms in just twelve months. Salmon takes three times as long. And the fish species is robust and can cope with various different environmental conditions. Cobia lives under deep-sea salinity conditions of between 32 and 35 parts per thousand but also for short periods in brackish water with considerably lower salinities. Experiments have shown that juveniles can be kept for several weeks at 5 parts per thousand without their growth suffering seriously. But what is much more important is the fact that the species is not very demanding with regard to diet. The carnivorous cobia has a high protein requirement but this can be partly satisfied with vegetable alternatives, for example with soy, hemp or yeast proteins. During rearing of fry, up to 40% of the fishmeal in the feed can be substituted without compromising growth. Researchers from the University of Maryland have even tested a completely fishmeal-free, purely vegetarian feed successfully during rearing. They believe that cobia can utilize carbohydrates more effectively than most other carnivorous fish species.

China is the biggest producer of cobia in aquaculture. Chinese production is mainly located in the southern coastal provinces Guangdong and Hainan and has in the meantime reached a level of nearly 40,000 t. With that, according to FAO statistics China currently produces about 80% of total global volume, clearly ahead of Taiwan that ranks second with about 2,000 t. Of the 14 countries that the FAO lists as regular or occasional producers of cobia are the USA, Mexico, Vietnam, Puerto Rico, Belize, the Philippines, the Dominican Republic and the Bahamas, Indonesia and Brazil. Panama is listed with a total production of 2,459 t in 2014, all of this quantity coming from the company Open Blue which operates the world’s biggest offshore farm for cobia 12 km off the Caribbean coast. In the meantime Open Blue has probably nearly doubled its production.

 

Still reserves in the technology for Cobia farming

The fry needed for commercial aquaculture facilities today comes without exception from hatcheries. Fry can be produced relatively inexpensively in open air ponds or in intensive recirculating systems which involves higher costs. In Taiwan, that is particularly successful with cobia hatching, farmers prefer to use onshore ponds that are as a rule 400 to 600 square metres in size and 1.5 m deep. They are filled with up to 100 fishes that are ready to spawn in a sex ratio of 1:1 and these spawn naturally at water temperatures of between 23 and 27°C throughout the year so that freshly fertilized eggs can be harvested almost every day and transferred to the grow-out tanks. Cobia larvae are very tiny and measure just under 4 mm but, compared to other marine fish larvae of this size, they are amazingly robust and resilient. In the USA plastic tanks are used for spawning, mostly with a diameter of about 6 metres and just under 2 metres deep. They can be operated as raceways, recirculating systems or in a combination of the two techniques. The spawning act takes place either naturally or after photothermal manipulation during which the altered seasonal rhythm of light and temperature induce the maturation processes outside the usual spawning time. After the yolk sac has been consumed the cobia larvae are first fed on enriched live feed (rotifers, Artemia nauplii) but this is quite complicated and very expensive. That is why work is being done to bring the transition to dry feed as far forward as possible.

When they reach a weight of 100 to 150 grams the fry are usually transferred to grow-out tanks where they grow to a marketable size. Occasionally this takes place in recirculating systems but the majority of producers prefer floating net pens in the sea that are mostly anchored offshore close to the coast. Such nearshore facilities are easily and quickly accessible but are considered to be less ecologically sustainable, or sometimes even seen as a threat to the environment. When kept permanently in shallow water off the coast, deep-sea species such as cobia are more at risk from outbreak of disease and parasite infestation, and the quality of their meat is also said to be poorer. For that reason some producers favour offshore regions for cobia grow-out. This demands much higher production costs but offers the fish conditions that are more in line with their natural habitat. A prime example of this strategy is Open Blue which produces cobia in offshore net pens in an ecologically sustainable way, largely stress-free and without hormones, growth promotors or antibiotics. In the world’s biggest offshore farm 12 km away from the coast the fishes are kept in what can be said to be their original natural environment. They swim constantly in a high-energy current and so they produce more muscle. Apart from that, offshore farms cause less environmental damage than fish farms located directly on the coast.

 

Excellent flavour in numerous variants

In upscale restaurants the few red muscle areas of the fillet are usually removed so that the individual portions are completely white.

 

With its round, almost cylindrical body cross section, cobia enables relatively high slaughter yields of over 50 per cent. However, processing this fish requires a great amount of strength, expertise and experience. The filleting knives that are usually used in fish processing are hardly capable of cutting through the tough, leathery skin and the very hard bones of the cobia. Anyone who has never filleted a fish before is probably well advised to pass this fish by for despite its size and allegedly favourable body proportions the species is definitely not a suitable fish for practising on. Even cutting steaks, i.e. simple transverse slices from the fish’s body, is likely to be too much for many people. If possible one should leave the demanding job of filleting cobia to a knowledgeable expert, for example a qualified fishmonger. Anyone who follows the advice to buy ready fillets will soon be rewarded: whether with or without the skin is immaterial for when fried the skin (which had seemed so obstinate during filleting) becomes very tender, crispy, and delicious and is a pleasure to eat.

The culinary advantages of cobia include that this fish can be prepared in many different ways. In Asia, cobia is often traded live and only killed directly before consumption. Due to its high fat content the fish is very good for sushi and sashimi, particularly since the dorsal loins which are preferred for this purpose can be cut into extremely thin slices without tearing. Cobia also maintain this quality during frying, grilling and deep-frying. Whereas fresh cod fillet often falls apart into the individual muscle areas during frying, cobia pieces remain much more firmly intact. Because the fish has a pleasant flavour and doesn’t smell fishy it is gladly used for raw or subtly marinated preparations, for example marinated tartare, ceviche or tataki for which raw or marinated fillet pieces are coated several times with a glazing containing sugar and then caramelized using strong, direct heat. This leads to a tasty crust on the fish’s exterior whilst inside the tataki remains raw. Cut into thin slices tataki is served as a starter or small snack in between. 

Cobia is perfect for sushi and sashimi. Fillets and dorsal loins can be cut into paper-thin slices without tearing.

Ceviche originally comes from Peru but has in the meantime spread to almost the whole of Latin America and even to Europe. The production of this dish is reminiscent of tartare but with the difference that in the case of ceviche the finely cut raw fish is marinated in lime juice and afterwards mixed with chopped onions and other ingredients. The acidity of the lime juice denaturalises the fish protein so that strictly speaking the fish is no longer raw. Cobia can also be steamed, poached or cold smoked. The very fat-rich belly flaps are a particular delicacy – like the toro cuts of tuna – and are best eaten raw. In Taiwan the liver of the fish is used for pâtés, terrines and similar products.

Fast growth, great flavour, excellent flesh quality and the fish’s suitability for almost all farming systems make cobia one of the most promising candidates for aquaculture. Nearly all experts predict a clear production increase and many even expect that cobia can become one of the most important fish species for mariculture whose development is just beginning. What could hinder this expected market success is really only the fact that hardly any consumers in the western world are familiar with this fish which – on top of that – is not exactly cheap. The price for cobia will probably fall in the future when production increases further so that it will mainly be lack of familiarity that will be the problem. But that seems solvable, even without complicated marketing, for the fish will advertise itself. Anyone who has tried cobia will almost certainly recommend it to others.