Caballero B. (ed.) Encyclopaedia of Food Science, Food Technology and Nutrition. Ten-Volume Set

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of the same age will measure 39 cm. The sea-bed to

the southern North Sea is warmer than that of the

northern North Sea, and this is not simply because of

the difference in latitude but because of the greater

depth. The deeper water of the north is cut off in

summer from the warmer zones by the formation of

a discontinuity layer. In the much shallower south,

where the water is more disturbed, no marked separ-

ation of upper and lower layers takes place, and so the

sea-bed is kept warmer, and the fish grow more

quickly.

0011 Spawning takes place at various points in the very

large area over the northern North Sea and in a much

smaller isolated patch just north of the Outer Hebri-

des. It is still not known to what extent the Hebridean

spawners are linked to the main North Sea stock. The

positions of spawning within the large area are

not fixed; their centers shift from place to place in

different years.

0012 Until the small embryo fish begin to produce their

characteristic pigment, it is exceedingly difficult to

distinguish the eggs of the haddock from those of

the cod, and they are often found floating together.

They drift and develop, as do those of the cod, but the

fry remain in the plankton longer and so do not seek

the bottom until they are over 5 cm long. Since the

young haddock are larger than the young cod when

they first settle down to a bottom-living life, they can

be caught more easily.

Whiting

0013 Among the four members of the genus Gadus that

lack the barbell, the whiting, G. merlangus, is the

most notable. It forms a considerable part of

the catch of North Sea trawlers and seiners and is

also abundant in the English Channel and Irish Sea;

indeed, it is the most important demersal species for

the fishermen of Northern Ireland. The catches in the

North Sea have indeed been increasing since 1982,

and it has been estimated that the total European

catch for human consumption from this area was

140 000 tonnes with, in addition, some 30 000 tonnes

of smaller fish taken for fishmeal. The whiting

spawns principally in April and May throughout the

North Sea but mainly within the 90-m line. In their

pelagic phase, after reaching 2 cm in length, the

young whiting associate with jellyfish, particularly

Pelagia cyanea, which become very abundant in

June; they shelter under the bell and appear to swim

among the tentacles without coming to any harm.

When almost 6 cm in length, they go down to the

bottom. In their first 2 years, they are found in

greatest numbers between the latitudes of 55 and



N. Like the hake and cod, the whiting feeds

largely upon smaller fish, but at times may also take

large quantities of the more active swimming

crustaceans, such as shrimps, prawns, mysids, and

euphausiids.

See also: Fish: Introduction; Catching and Handling

Further Reading

Gerking SD (1994) Feeding Ecology of Fish. San Diego,

CA: Academic Press.

Gomes MC (1993) Predictions under Uncertainty. Fish

Assemblages and Food Webs on the Grand Banks of

Newfoundland. St John’s, Canada: ISER, Memorial

University of Newfoundland.

Hoines A, Bergstad OA and Albert OT (1995) The food

wed of a coastal spawning ground of the herring (Clupea

harengus L.) In: Skjoldal HR, Hopkins C, Erikstad KE

and Leinaas HP (eds) Ecology of Fjords and Coastal

Waters. Amsterdam: Elsevier Science.

Jobling M (1995) Environmental Biology of Fishes.

London: Chapman & Hall.

Laevastu T (1996) Exploitable Marine Ecosystem: Their

Behaviour and Management. Oxford: Fishing News

Books.

Pelagic Species of Temperate

Climates

G D Khedkar and B V Jadhao, Dr. Babasaheb

Ambedkar Marathwada University, Aurangabad,

Maharashtra, India

C D Khedkar, College of Dairy Technology, Warud

(Pusad), India

N V Chavan, Adarsha College, Hingoli, Maharashtra,

India

Background

0001The pelagic species found in summer throughout the

waters of the European continental shelf are continu-

ally on the move in search of food; they feed on small

fish such as sprats and sand eels, as well as on krill

plankton. These species move between the surface

and lower layers of the sea (2–400 m), depending

upon the season and topographical features of the

sea-bed. As surface-feeders, they have long provided

a useful and easily caught source of food. Although

the individual species are distinct, the group overall

has a number of unifying features that tend to

influence its exploitation and utilization by humans.

2428 FISH/Pelagic Species of Temperate Climates

Mackerel

0002 The scientific name of the mackerel caught in the

north Atlantic is Scomber scombrus. Other species

of Scomber, and species of Scomberomours, Auxis,

and Restrelliger, are also described as mackerel in

many parts of the world. The name mackerel is used

in the UK principally for the species Scomber scom-

brus, but the name can also be used in the UK for any

species of Scomber offered for retail sale. Scomber

scombrus is sometimes called Atlantic, northern or

Boston mackerel, to distinguish it from Scomber

japonicus, which is variously called chub, Pacific, or

Spanish mackerel. A small mackerel is sometimes

called a cock mackerel, a joey or a little boy in

England, or a pinner in Scotland.

Distinguishing Features

0003 The Atlantic mackerel has a rounded, elongated body

with two widely spaced back fins, the first with 11–13

spiny rays, the second with soft rays; the club mack-

erel has nine or 10 spines in the first back fin. There

are four to six (usually five) finlets between the

second back fin and the tail, and between the anal

fin and the tail. There is a small keel on each side of

the tail stub. The tail is forked. The back of the

mackerel is a brilliant greeny blue, and the head is a

steely blue–black with a small yellow patch behind

the eye. There are 23–33 dark wavy bands across the

back of the fish down to the midline. The sides have a

silvery or coppery sheen, the belly is silvery white, and

there is a broken black line just below the lateral line.

The scales are small, and the skin feels velvety. There

is a swimbladder in the chub mackerel but not in the

Atlantic mackerel.

Life History

0004 At the start of the winter, the mackerel migrate to

overwintering areas. These are not well defined, but

three are known around UK, one in the North Sea

along the Norwegian Deeps, another along the edge

of the continental shelf in the western Celtic Sea, and

a third close to the south coast of Cornwall. The first

two are typical overwintering areas and are similar to

those off the east coast of North America; the mack-

erel are mixed with other species, for example scad

in the Celtic Sea and Norway pout in the North Sea.

Off Cornwall, the pattern is different. Large shoals

of mackerel with few other fish among them

move close inshore into relatively shallow water, al-

though separate shoals of pilchard and scad are found

in the area. The Cornish stock of winter mackerel was

unknown before the mid-1960s, presumably because

it was not there, and it is assumed to be an unstable

offshoot of the stock in the Celtic Sea. Should

the unknown factors that attracted the shoals

suddenly change, there is always the possibility that

they may withdraw just as suddenly from the area;

nowhere else in the north Atlantic are adult mackerel

found in a comparable position. Mackerel do not feed

while overwintering, but they are not totally inactive.

They form large dense shoals near the sea bed during

daylight but rise and disperse during darkness. Occa-

sionally, they disperse for no obvious reason and

reform hours or even days later many miles from their

previous position. Mackerel begin to move away from

the overwintering areas in the spring to spawn and to

start their feeding migrations. Spawning begins along

the edge of the continental shelf in southern Biscay

during February. By late March, spawning occurs

throughout the Bay of Biscay and the Celtic Sea, and

to the west of Ireland, and continues until June, but at

all times, the greatest concentrations of eggs are found

along the edge of the shelf. The older, larger fish start

spawning first and, when spent, start swimming north-

wards along the edge of the shelf towards Shetland.

Smaller, younger fish start spawning later and do not

migrate so far. The youngest fish remain in the Celtic

Sea throughout the summer. The spawning season in

the North Sea is later, from May to August, and is most

productive north of the Dogger Bank. Those that

spawn south of the Dogger Bank are part of thewestern

overwintering stock that spawns and feeds in the

southern North Sea. Once spawning is completed,

the North Sea mackerel mix with the older fish from

the western stock around Shetland until the winter

migration begins. Each female mackerel spawns on

average about 300 000 eggs, which, when fertilized,

are about 1 mm in diameter. Each contains a large oil

globule that helps it to float in the upper water layers

until it hatches. The larvae, 2–3 mm long, hatch after

4.5 daysat 15



C, or 8.5 days at 10



C, and by the end of

the first year, the young mackerel are 15–20 cm long.

Growth continues to be rapid, and by the end of the

first year, the young mackerel are 28–34 cm long. The

growth rate is then considerably reduced, and mack-

erel 35–40 cm long may be anywhere between 5 and 20

years old. While a large fish is usually an old fish, one

mackerel 57 cm long was found to be only 6 years old.

Length and Weight

0005An adult mackerel 30–35 cm long weighs 300–500 g

before gutting. A joey mackerel, 20–25 cm long and

probably in its second year, weighs 100–200 g. Mack-

erel weighing more than 1 kg are exceptional.

The Mackerel Fishery

0006Large, dense shoals may be found near the surface all

round the UK in the summer and autumn, but their

occurrence is sporadic in the southern North Sea.

FISH/Pelagic Species of Temperate Climates 2429

The English summer mackerel fishery was tradition-

ally from April to September; this has now been

extended from February to October so that, coupled

with the huge winter fishery now established in the

southwest from October to March, mackerel supplies

are available throughout the year. The Scottish mack-

erel fishery from June to August could also possibly

be extended. Mackerel fishing methods have changed

dramatically over the past 50 years. Before 1939,

mackerel were caught mainly in the spring by drift

net, an interim occupation for drifters between the

winter and summer herring fisheries. After 1945,

mackerel landings were small for some years, and the

catch was taken mainly in the southwest during

the summer by feathering, that is, small boats using

hand lines with colored lures made from feathers or

plastics. Once the mackerel shoals were found to

remain in Cornish waters throughout the winter, the

hand-line catch increased considerably in the late

1960s. As the market for mackerel improved,

trawlers began to engage in mackerel fishing, using

midwater mackerel in quantity off the west of Scot-

land in late summer.

Composition of Mackerel

0007 The mackerel is a fatty fish, and the fat and water

content vary with season. The fat content of mackerel

caught off southwest England is lowest in May after

spawning and reaches its peak between October and

December after the fish have fed during the summer

and autumn. A typical range of fat content through-

out the year is 6–23%, and the protein content is 18–

20%. The fat content of mackerel caught off the west

coast of Scotland during August and September is

similar to that of Cornish mackerel during December

and January.

Herring

0008 The herring, Clupea harengus, is the most plentiful fish

found in the north Atlantic. C. pallasi is a closely

related herring species found in Pacific. So important

is it in sea life that it is given pride of place. It is known

as a creature very well adapted for living in the upper

water layers. Its blue–green back matches the color of

the depths when viewed from above, and its silver

flanks, seen from the side or below, mirror the varying

lights and shades of the surrounding waters.

Distinguishing Features

0009 The body of the herring is deeper than it is thick, and

the length of the fish is about five times the greatest

depth. The upper part of the body is dark blue–green

or steel blue, the snout is blackish blue, and the sides

and belly are silvery. The lower jaw protrudes slightly

beyond the upper jaw. There is a single short back fin,

a short anal fin near the tail, and a deeply forked tail

fin. The pelvic fins are behind the start of the back fin,

whereas on the sprat (Sprattus sprattus), they are in

front.

Life History

0010Nearly all the other sea-fish of commercial impor-

tance lay eggs, which float freely in the water, drifting

as part of the plankton; the herring is an exception

and deposits its spawn in masses on the sea-bed,

particularly on a gravel bottom, thickly plastering

stones, shells and even the backs of crabs with it. As

soon as the eggs are laid, they sink and stick to what-

ever they touch. In the summer when the fish are

feeding, they are perhaps in smaller shoals, but now

it seems that these combine together as the spawning

time approaches. Some shoals are said to be 13–

15 km long and 3–5 km wide. Each herring lays at

least 10 000 eggs, and so the quantities of spawn

produced by a shoal are enormous. The spawning

grounds are an attraction to many bottom-living

fish, especially haddock, which gorge themselves on

this rich food. The eggs are fertilized in the water by

the male herring, which discharge their sperm at the

same time as the females lay their eggs. In North

America, native Indians have long collected these

eggs as a seasonal delicacy, and nowadays, an entire

industry is centered on the collection of herring eggs

for export, mostly to Japan. The eggs are about 1 mm

in diameter and are incubated for 10–30 days

depending on the sea temperature; 14–20 days is

typical for the North Sea. The newly hatched fry or

larvae, with yolk sacs attached, are 6–10 mm long

and planktonic, and drift with the current. Since

they depend upon nearby supplies of plankton for

food, population levels can be directly affected by

changes in the availability of the zooplankton.

When the larvae reach a length of 40 mm, they

begin to develop scales, take on a silvery sheen and

move to inshore nursery grounds. Here, they are often

caught, together with the young of other fish. The

small fish now collect together in shoals, and tend to

come in towards the coast into shallow water and

sometimes large estuaries like the Thames or the

Wash in the UK. In the Thames estuary, enormous

shoals of whitebait are fished by so-called stow nets,

which are huge conical nets lowered below anchored

vessels and streamed out with the ebb and flow of the

strong tides. After a sojourn of some 6 months or so in

the estuaries and coastal regions, the herrings appear

to scatter over the North Sea. They do not join the

main shoals until they become sexually mature for

the first time, and this, curiously enough, occurs in

different individuals from the ages of 3–5 years.

2430 FISH/Pelagic Species of Temperate Climates

Body Length

0011 Most of the herring landed in the UK are between 230

and 300 mm long; herring caught off Norway and

Iceland are often larger, up to 360 mm. Occasionally,

herring can reach a length of about 430 mm, but this

is exceptional.

Herring Fishery

0012 In Scotland, there are several small fisheries at the

beginning of the year. In the Minch, between

the Outer Hebrides and the mainland, there is a fish-

ery first for spent fish, then for recovering spents, and

later on, in February and March, a stock of early

spawning fish comes in. In the Firth of Forth area,

there is a fishery for full and filling fish in January,

extending to one for spawning fish in March. In

Ireland, there are two fisheries for full and filling

herring and later for spawners, one at the north and

one in the southeast; both are over by the end of

February. April and May is a lean period of poor

fisheries, mainly for recovering spents. The small

fishery at Lowestoft does not always materialize. In

Ireland, too, they catch recovering spents in both the

north and south in May, and sometimes in the south

in April. During June to August, there is the great

summer fishery in the northern North Sea for good-

quality full and filling fish, the herring having nour-

ishing themselves on the rich crops of zooplankton. In

England, the drift-net fishery is confined to the North

Shields area, where immature and recovering spents

are caught in June, and full and filling fish in July and

August.

0013 The ring nets are employed for the herring fishery.

A shoal of fish is located either by echo-sounding or

by a feeling wire (a wire that gives a tremor when it is

hit by the passing fish) and then surrounded by a net

cast out as the boat circles around. Herring do not

spend all their time near the surface; for a good part

of the daytime, they are near the bottom, and a

knowledge of this habit has led in recent years to

another new and very considerable development:

fishing for them with special fast trawls that skim

over the bottom and have their head ropes kept

very high by extra floats or underwater kites. The

Germans were the pioneers in this and, for many

years, have operated a large fleet of herring trawlers,

working particularly on the Fladen grounds. During

July and August, some of the companies in Hull, UK

have also adopted this type of fishing in the North

Sea. Fishing off the Yorkshire coast is in full swing

during September, with landings at Whitby, Scarbor-

ough, and Grimsby, but by the end of September, all

the drifters are concentrated at Yarmouth and Low-

estoft ready for the great October and November

fishery for the immense shoals of fine-quality full

and filling that flood the East Anglian grounds prior

to spawning in the Channel. This is the climax of the

year; there is no more important herring fishery else-

where in the world.

Processing and Preservation of Pelagic Species

0014Pelagic fishes are fatty and are not normally gutted at

sea; they therefore spoil quickly unless they are chilled

immediately after catching and kept chilled. They

develop off odors after 1–2 days at 10



C, become

soft and spoil rapidly after 3 days, and become putrid

after 5–6 days. Stale or noticeably spoiled fish should

not be used for processing. In stale fish, the eyes are

sunken, cloudy, and discolored red or brown. The

skin loses its bloom, and its colors lose their intensity

and brilliance, giving a washed-out appearance. The

gills are dark red or brown, and a dark blood red

mucus oozes from the gill covers. The odor of the

gills and body is sour, sweaty, or strongly oily; some-

times a smell of ammonia is also present.

Chilling and Freezing

0015For freezing, the fish should be chilled immediately

after capture and frozen within 24 h. Frozen fish

should be properly glazed and kept in cold storage

at 30



C, which will keep it in good condition for at

least 6 months. The cold-storage life can be extended

up to 1 year if the fish is packed in polyethylene bags

topped up with water and frozen in vertical freezers.

The block is doubly protected against deterioration in

storage by the encasing ice and packaging. Gutt-

ing before freezing is not necessary and may be a

disadvantage. The fish can be hot-smoked to give a

ready-to-eat delicatessen product, and the flesh of the

hot-smoked fish can be used as a basis for a pa

.It

can also be split or filleted and then kippered in cold

smoke in a manner similar to herring. For a product

of good eating quality, a fish with a fat content of at

least 10% should be used. The smoked product can

be whole gutted fish, with or without the head on, or

fillets. Smoked whole fish is gutted, or headed, and

gutted as required, the gut cavity cleaned, and the

black bellywall lining removed. For hot-smoked

fillets with skin left on are cut from the whole fish.

Brining requires some care. In order to minimize the

risk of food-poisoning organisms growing in the fin-

ished product, it is recommended that the salt concen-

tration in the water phase of the product be at least

3%. This concentration, expressed in terms of water

plus the solid components of the flesh, is less than

3%. To measure the salt concentration in the water

phase, it is also necessary to measure the water con-

tent of the product. A salt concentration of 3% does

FISH/Pelagic Species of Temperate Climates 2431

not render hot smoked fish unacceptably salty to the

consumer. The rate of uptake of salt during brining

depends principally on the size of the fish; large fish

take longer to brine than small fish. Thus, to achieve a

reproducible uptake of salt, all the fish in a batch

should be of roughly the same weight. The brined

whole fish can be tied by the tails in pairs and hung

over tenter rods for smoking, or hung individually by

the tails in keyhole slots cut in metal frames designed

for the purpose. Fillets are laid on trays made of

nylon-coated or stainless steel wire mesh. Full tenters,

speats, or trays are loaded on to trolleys, which, when

fully loaded, can be left to drain for 1–2 h or wheeled

directly into the kiln without draining. In kilns with

more than one trolley, the first loaded trolleys should

be positioned at the air-outlet end, and the last loaded

trolley at the air-inlet end. The smoking procedure in

a mechanical kiln is as follows. With the kiln thermo-

stat first set at 30



C, the air-inlet half to threequarters

open, and the main fan and chimney fan on, the

smoke producer is set to produce maximum smoke,

the recirculation damper being set to balance the

smoke pressure in kiln. This predrying and smoking

period takes about 1 h, during which time, surplus

moisture dries off the surface of the fish, and the

skins begin to set. The thermostats are then reset at



C, the air inlet reduced to a quarter open, and the

smoke pressure balanced by resetting the recircula-

tion damper. The temperature and humidity in the

kiln begin to rise, and the fish start to cook; high

humidity prevents excessive weight loss. Once the

temperature reaches 50



C, it should be kept at that

temperature for 30 min. The skin of the fish then

becomes firm, and color begins to develop. For the

final cooking stage, the order of the trolleys is re-

versed. The thermostats are reset at 80



C, the air

inlet closed, and the recirculation damper opened

only just enough to relieve any back-pressure on the

smoke producer. By the time the kiln temperature

reaches 80



C, small fish need a further 40–45 min

to complete the process; larger fish need about

75 min. As a rough guide, the whole smoking process

should take about 3 h. The fish attain a dark golden

brown color, and the skin is dry with a silky sheen.

The flesh should be completely cooked; the thickest

part of the flesh at the shoulders of a whole fish

should be opaque, with no jelly-like flakes.

Canning

0016 These fishes may be canned as steaks, as fillets in a

variety of sauces, or as a cold-smoked product. To

make canned steaks, the whole fish are headed and

gutted, and the belly cavity is cleaned out. The black

skin is removed from the belly wall, and traces of

blood along the backbone are brushed away. The

fish are then cut into steaks of a length to suit

the pack. The pieces are packed vertically in the can

to give a product that resembles a middle-cut steak of

a large fish. After adding 3 g of salt, the can is closed

and heat-processed for 90 min at 115



C. Vegetable

oil or tomato sauce can be added to the can before

closing. The finished cans should be stored for about

1 month before labeling and distribution; there is no

further significant change in flavor or texture during

storage after that time.

Salting

0017Quantities of fish were at one time pickle-cured in

barrels for export, and small amounts are still packed

in this way. A typical process is as follows. Fresh fish

are split along the back and opened with a jerk to

break the ribs. For hot-smoked fillets, skin left on is

cut from the whole fish. Guts, gills, and any protrud-

ing bones are removed, and blood is washed away

from the backbone. The fish are then soaked in fresh

water for up to 2 h, rinsed, drained, and then dipped

in dry salt. The fish are packed in barrels in circular

fashion with tails to the center, and salt is sprinkled

on each layer. The first two or three layers are packed

skin downwards, and successive layers skin upwards.

About 1 kg of salt to 3 kg of fatty fish or 4 kg of lean

fish is required throughout the pack. When the barrel

is full, it is closed, laid on its side, topped up with

brine through the bung, and left for 10–12 days,

further brine being added, if required, to keep the

barrel full.

See also: Canning: Principles; Fish Farming; Freezing:

Principles; Preservation of Food

Further Reading

Bligh EG (1992) Seafood Science and Technology. Oxford:

Fishing News Books, Blackwell Scientific.

Burt JR, Hardy R and Whittle KJ (1992) Pelagic Fish: The

Resource and its Exploitation. Oxford: Fishing News

Books, Blackwell Scientific.

Grahame J (1987) Plankton and Fisheries. London: Edward

Arnold.

Gregoire F (1993) Biological characteristics of Atlantic

Mackerel (Scomber scombrus L.) sampled along the

Canadian coast between 1983 and 1991.

Lockwood SJ (1988) The Mackerel – Its Biology, Assess-

ment and the Management of a Fishery. Oxford: Fishing

News Books, Blackwell Scientific.

Scott WB and Scott MG (1988) Atlantic Fishes of Canada.

Canadian Bulletin of Fisheries and Aquatic Sciences

Number 219.

SFIA (1989) Pelagic Species Review – Resources and

Markets. Report No. 2002. Edinburgh: Sea Fish Indus-

try Authority, Market Development Department.

2432 FISH/Pelagic Species of Temperate Climates

Tuna and Tuna-like Fish of

Tropical Climates

G D Khedkar and B V Jadhao, Dr. Babasaheb

Ambedkar Marathwada University, Aurangabad,

Maharashtra, India

C D Khedkar, College of Dairy Technology, Warud

(Pusad), Maharashtra, India

N V Chavan, Adarsha College, Hingoli, Maharashtra,

India

Background

0001 Over the last two decades (1981–2001), tuna has

become one of the most commercially important

fish species, a source of foreign exchange earnings

for many developing countries. Initially, larger fishing

nations dominated the industry, but with the intro-

ductin of the 200-mile (roughly 320-km) exclusive

economic zone, an increasing number of developing

countries now take advantage of their tuna resources.

Important fisheries exist throughout tropical and

temperate areas of the world’s oceans. Although

tuna constitutes less than 3% of the world fish pro-

duction, it is one of the most valuable fisheries. The

southwest Pacific is the main tuna fishing area and

accounts for one-third of total catches. The eastern

Central Pacific was overfished in the early 1980s,

leading to a drop in production in 1984. There was

a subsequent fleet movement to the southwest Pacific.

As a result, yellowfin resources recovered. Tuna has

many uses in the Western nations. A number of tuna

utilization possibilities have emerged in the tropics.

Internationally, tuna is traded fresh, frozen, or

canned. Japan remains virtually the only major

market for fresh tuna, much of which is consumed

as sashimi. Tuna for the sashimi market is deep frozen

to temperatures below 40



C. The sashimi market is

sensitive to quality-size, fat content, and method of

handling the fish. Normally, larger fish with a higher

fat level are preferred. Most of the frozen tuna inter-

nationally traded is eventually canned. Canned tuna

is generally presented in the following product forms:

solid, chunk, flakes, grated, and smoked. A small

quantity of tuna is traded for use as pet foods, oil,

and tuna meat. Principal uses of internationally

traded tuna are canning, other forms of processing,

or special Japanese products. Different parts of the

fish are used for different product types. For canning,

the firmer loins are used for ‘solid pack,’ and those

less firm or broken are used for ‘chunks.’ The

scrapings, which are not blood, meat, or skin, are

collected and sent to the flake or grated lines.

Table 1 lists the characteristics of several commer-

cially important tropical species of tuna.

Characteristics of Major Tropical Species

of Tuna

Skipjack (

Katsuwonus pelamis

)

0002Skipjack is usually 45–80 cm in length and 3–6kg in

weight (Figure 1a). This species is primarily frozen

and used as a raw material for canning. In Japan,

skipjack is also smoked and dried for katsuobushi

production. The landings of this fish have increased

steadily over the last 40 years from 25% of world

tuna production in 1965 to 32% in 1975, 48% in

1988, and 51% in 1997. Skipjack replaced yellowfin

as the most important component of total tuna land-

ings in 1972 and has since consistently accounted for

the majority of total landings. Japan has traditionally

been the most prominent producer of this fish,

but in recent years, the USA, France, and Spain

have increased their operations. Several developing

countries such as Indonesia and the Philippines have

also emerged as important producers. Thailand has

emerged as a major market for fresh and frozen skip-

jack in recent years, importing an estimated 250 000

tonnes in 1988 and surpassing the USA as the world’s

most important frozen skipjack import market.

Major markets of canned skipjack are the USA, UK,

and Germany.

Yellowfin Tuna (

Thunnus albacares

)

0003Yellowfish tuna is usually 70–150 cm in length and

7.2–150 kg in weight (Figure 1b). A major use of this

fish is freezing and processing as canned fish for

markets in western Europe, the USA, and Japan.

Japan also uses yellowfin on the sashimi market.

The landings of this fish have increased in recent

years, due to new purse seine fisheries in the Western

Indian Ocean and the Pacific. The largest importer of

frozen yellowfin is Italy. In 1987–88, Italy imported

100 000 tonnes as a raw material for its canneries.

Japan and the USA are the second and third most

tbl0001Table 1 Some commercially important tropical species of tuna

Common name Scientific name Size Weight

Yellowfin Thunnus albacares 160–200 cm 40–130 kg

Bigeye Thunnus obesus 90–180 cm 20–80 kg

Bluefin

Northern bluefin Thunnus thynnus 160–200 cm 40–130 kg

Southern bluefin Thunnus maccoyii 160–200 cm 40–130 kg

Skipjack Katsuwonus pelamis 48–80 cm 3–6 kg

Albacore Thunnus alalunga 40–90 cm 4–15 kg

FISH/Tuna and Tuna-like Fish of Tropical Climates 2433

important markets: Japan imported 50 000 tonnes

annually in addition to its domestic production

during the 1980s, while the USA imported 40 000

tonnes.

Albacore (

Thunnus alalunga

)

0004 Albacore usually weighs 4–15 kg, with a length of

40–90 cm (Figure 1c). This is a cosmopolitan fish,

occurring in tropical waters of all oceans. At least

two stocks (northern and southern) exist in both

the Atlantic and the Pacific oceans, with little or no

interchange across the warm equatorial waters. The

northwest Pacific is the most important fishing area,

followed by the northeast Atlantic and eastern Cen-

tral Pacific. The landings of this species varied

between 180 000 and 225 000 tonnes from 1975 to

1988, but a general decline in annual production is

evident. Japan and Taiwan each account for approxi-

mately one-third of the world’s annual albacore

production. Most of the albacore production is in

canning in the USA as solid whitemeat tuna. The

USA is a major importer, averaging 70 000 tonnes

annually. Some albacore is sold as fresh and canned

fish, and consumed in local markets in France and

Spain.

Southern Bluefin (

Thunnus maccoyii

)

0005Southern bluefin typically weighs 40–130 kg, with a

length of 160–200 cm (Figure 1d). It occurs in south-

ern oceans at a latitude of 39



S. The fishing areas

south of Australia, in the Tasman Sea, and in the

Eastern Indian Ocean account for 70% of total

annual production. The catch varied between

33 000 and 47 000 tonnes annually during 1975–88.

Management measures were introduced by Australia

in the 1980s to prevent overexploitation of the

species, and production levels have since declined to

19 000 tonnes in 1989. Australia and Japan are the

principal producers, consistently accounting for more

than 85% of total production worldwide. The fish is

generally sold fresh on the sashimi market in Japan,

where it may fetch as much as US$35–45 kg

1

Bigeye tuna (

Thummus obesus

)

0006Bigeye tuna typically weighs 20–80 kg and is

90–180 cm in length (Figure 1e). This species is

(a) (b)

(e)

fig0001 Figure 1 Commercially important species of tuna from tropical climates. (a) Skipjack (Katsuwonus pelamis); (b) Yellowfin tuna

(Thunnus albacares); (c) Albacore (Thunnus alalunga); (d) Southern bluefish (Thunnus maccoyii); (e) Bigeye tuna (Thunnus obesus).

2434 FISH/Tuna and Tuna-like Fish of Tropical Climates

distributed in tropical and subtropical seas but is

absent from the Mediterranean. World production

of this fish during 1980–90 was approximately

200 000 MT annually. The eastern Central Pacific

has traditionally been the most important area, ac-

counting for a third of the total bigeye production.

Japan, South Korea, and Taiwan are the only produ-

cers with selective fishing gears targeting bigeye, and

Japan is the largest consumer of bigeye. Although

some of the production is frozen, most is sold as

fresh fish and sold on the sashimi market.

Quality Requirements for the Tuna Market

0007 The raw material must be handled carefully so as to

prevent bruising and damage to the flesh. Thus, long

lining is the best method of catching tuna for export,

since damage is minimal. The flesh of fish killed under

stress undergoes chemical changes, a condition called

‘burning,’ which causes the flesh to become mushy and

inedible. Speed and accuracy are needed in processing

tuna for export. Fish has to be bled, gilled, gutted, and

chilled rapidly. Tuna for the sashimi market is graded

not only on visual characteristics such as a bright/

clear skin, clear and moist eyes, elastic skin, and

undamaged smooth abdominal walls but also on the

fat content of the flesh. A small flap is cut in the tail

region to inspect the color and feel for the oil content.

0008 In most buyer countries, tuna imports are generally

covered by food-safety regulations applicable to

fresh/frozen fish. The limits for heavy metals vary:

in Italy, the upper limit for mercury is 0.7 mg kg

1

and in Japan, it is 0.4 mg kg

1

. The permissible limit

for cadmium is 0.5 mg kg

1

in most buyer countries,

while lead levels vary from 0.5 to 2.0 mg kg

1

. Inter-

nationally, traded tuna is also tested for histamine, a

tuna muscle protein that causes vomiting, diarrhea,

and skin irritation if ingested at high levels. For most

buyer countries, the permitted levels vary from 200 to

500 mg kg

1

Internationally Traded Tuna Products

0009 Internationally traded tuna products include the

following

0010 chilled, deheaded and gutted, or gilled and gutted;

0011 frozen, deheaded, and gutted, or gilled and gutted;

0012 canned, ‘solid packs’ (a mixture of pieces of tuna);

0013 canned, ‘chunks’ (a mixture of pieces of tuna);

0014 canned, ‘flakes’ (smaller pieces of tuna);

0015 oil and meals;

0016 pet food and animal feed.

0017 The canned products are packed in oil, brine, or

sauce. A range of flavoring and seasoning additives

are used in canning, including salt, monosodium glu-

tamate, hydrolyzed protein, and various spices.

Smoked tuna products are also internationally traded

to a small extent.

Sashimi

0018The Japanese tuna market is distinct. It is centered on

raw consumption in a form called sashimi. The sash-

imi market demands large species such as bluefin,

bigeye, and, to a lesser extent, yellowfin. The sashimi

market is sensitive to quality-size, fat content, and

method of handling the fish. Normally, larger fish

with a higher fat level are preferred. The highest-

quality northern bluefin is used exclusively for high-

class restaurants, while the lower-quality product is

used for household sashimi. Southern bluefin is used

mostly by the restaurant trade, while bigeye use is

split between restaurants and households. Sashimi

processing involves progressive cutting of the flesh

into cuts and portions illustrated in Figure 2. Differ-

ent sashimi cuts (Figure 3) from different species have

various market values, depending on the fat content.

Those with a higher fat content have a lighter color.

Prime sashimi is ‘otoro’ (pink), followed by chutoro

(darker pink). Otoro and chutoro are types of toro

and have a fat content of about 25%. Inner muscle

blocks, more reddish in color with 14% less fat are

marketed as akami. Prices vary according to size,

season, freshness, moisture content, flesh texture,

and taste.

0019Dried/smoked tuna products, called fushi in Japan,

constitute a smaller but important percentage of

Japanese tuna products. Katsuobushi refers to skip-

jack fillets that have been boiled then broiled over

charcoal several times, dried, and then inoculated

with a mold during processing. Shavings of katsuo-

bushi fillets are marketed as kezuribushi. Arabushi is

Round Dressed Fillet

Fillet Loin Chunk

Steak (saku) Chunk (koro)

Semi dressed

(gillad, gutted)

fig0002Figure 2 Stages in the preparation of sashimi portions.

FISH/Tuna and Tuna-like Fish of Tropical Climates 2435

produced by drying and smoking skipjack loins, using

fish caught by pole and line. Namaribushi is similar to

arabushi, but the basic softness of the product is

retained by reduction of smoking period. Imports of

fishery products are in the form of arabushi, with the

final processing including mold inoculation being

done in Japan. Other products include tsukudani, a

tuna pickle made out of skipjack flesh, boiled and

seasoned with a solution of soya sauce and other

flavoring materials. Shiokara, a fermented product,

is produced from the viscera, stomach, or low-fat

meat of skipjack by a process of salt fermentation.

Nutritive Value of Tuna

0020 Tuna is very rich in high-quality protein. It is richer

than beef or chicken and is one of the best sources of

amino acids (Table 2). Tuna flesh contains substantial

quantities of vitamins A, B

, and D. It is also a very

rich source of phosphorus, iodine, and fluorine. Stud-

ies of tuna have shown that Katsuwonus pelamis

muscle consists of 69–72.6% moisture, 22.4–25.5%

protein, 1.6–2.6% lipid, and 1.5–2.4% ash; a lipid

content of up to 4.1% has been reported for some

temperate species. Anatomical fractionation has

yielded 69.7% meat and a total waste (head viscera)

of 30%, a meat–bone separation has yielded 84%

mince, and after heat processing and canning, the

amino acid content has been found to remain essen-

tially the same except for histamine and the sulfur

amino acids. Hence, the protein quality can be said to

be unaffected by precooking and retorting of canned

tuna. Thiamin shows about 5% retention in the

canned product. Nicotinic acid and riboflavin have

also shown some reduction, and minerals assayed

have shown a low retention. These losses might be

due not only to heat destruction but also leaching of

vitamins and minerals into the liquid portion of the

canned product.

Global Supply Trends for Tropical Tuna

0021The world catch has steadily increased since the

1980s due to fishing by fleets in Latin America and

Asian developing countries, the move of French and

Spanish purse seiners to the western Indian Ocean,

and increasing exploitation of western Pacific re-

sources. Japan is the largest producer, even though

its catch of high-value species has declined. The

catches of Spain, France, Indonesia, Mexico, and

South Korea have experienced the most growth. Skip-

jack continues to be the main species caught; 1.2

million tonnes were harvested in 1989. Yellowfin

catches increased from 500 000 tonnes in 1980 to

905 000 tonnes in 1989. The major fishing grounds

are in the southwest Pacific, accounting for about

one-third of the total worldwide catch. Other major

areas in order of importance are: eastern Central

Pacific, western Indian Ocean, Northern Pacific and

eastern Central Atlantic. The total canned tuna pro-

duction increased more than 50% from 602 000

tonnes in 1980 to 1 099 000 tonnes in 1989. More

than 80% of all catches are canned, 16% are

consumed as sashimi, and the rest are cured. The

leading country in canning remains the USA, which

produces around 275 000 tonnes per year. Thailand’s

canned production grew the most during the 1990s.

The share of developing countries in total canned

production increased from 16% in 1980 to 44% in

1989. Trade in fresh and frozen tuna reached 1.3

million tonnes in 1989, representing about 75% of

Chutoro

Toro grades

Akami

Otoro

Otoro Chutoro

fig0003 Figure 3 Distribution of cuts in tuna.

tbl0002Table 2 Comparative appraisal of nutrients in raw and canned

tuna

Nutrients Raw tuna Canned tuna

Essential amino acids (mg per 16 g of N)

Histidine 6.59 5.07

Isoleucine 4.49 4.47

Leucine 8.24 8.33

Lysine 8.79 8.67

Cystine 1.62 2.72

Phenylalanine 3.62 1.47

Threonine 4.57 3.81

Tryptophan 4.57 1.19

Valine 5.31 5.33

Vitamins and minerals (per 100 g)

Thiamin (mg) 189 11

Riboflavin (mg) 305 152

Nicotinic acid (mg) 28 19

Sodium (g) 0.27 2.39

Potassium (g) 0.91 0.63

Calcium (mg) 2.94 0.80

Iron (mg) 8.76 5.59

Copper (mg) 2.54 0.63

Source: Johnson AM (1993) Tuna and tuna-like species of tropical

climates. In: Macrae R, Robinson RK and Sadler MJ (eds) Encyclopaedia of

Food Science and Nutrition, pp. 1846–1850. London: Academic Press.

2436 FISH/Tuna and Tuna-like Fish of Tropical Climates

all tuna trade. Increase in the Japanese demand for

sashimi and canned yellowfin doubled fresh and

frozen imports from 1980 to 1989. Thailand is now

the largest importer of frozen tuna as it imports prac-

tically all the raw material for its canneries. Similarly,

Italy and the Ivory Coast, both dependent on raw

material imports, expanded purchases of frozen

tuna. The main suppliers of fresh chilled and frozen

tuna continue to be South Korea and Taiwan, mainly

selling to the Japanese sashimi market. Prepared/

preserved tuna exports reached 411 269 tonnes in

1989. Nearly 40% of total canned tuna production

entered international trade in 1989.

Global Demand Trends for Tropical Tuna

0022 Japan continues to be the main tuna-consuming

country – sashimi consumption has declined over

recent years, whereas canned tuna and katsuobushi

have expanded. The total per capita supply has in-

creased somewhat from 5.60 kg in 1980 to 6.35 kg in

1988–30% canned, 25% katsuobushi, and the re-

mainder sashimi. Per capita consumption in the USA

increased only slightly, from 2.4 kg in 1980 to 2.7 kg

in 1988. In Spain and France, per capita consumption

of canned tuna almost doubled. In Italy, canned tuna

accounts for about 20% of total fish consumption.

0023 Canned tuna is the most interesting product form

to watch. Despite dramatic adjustments in the indus-

try during the past decade, canned tuna’s share of

total consumption has remained at 80%. In Japan,

consumption is likely to expand further on the wave

of occidental food. By 2005, a per capita consump-

tion of 2.7 kg is predicted. The USA, however, has

reached saturation.

Prospects for Developing Countries

0024 Loining operation is one of the prospects for develop-

ing countries, especially for those in the Caribbean and

South America. In an attempt to contain production

costs, US canners operating in Puerto Rico are actively

considering options for loining tuna in lower-wage

countries. Bumble Bee and Star-Kist are already

importing frozen loins from Mexico, Equador, Costa

Rica, and Thailand. The preparation of loins for

canning is a labor-intensive operation. The cost

squeeze for US canners could provide the impetus to

perfecting the technology to allow loining to take

place away from the cannery location. US canners

have the advantage in that the main product form for

lightmeat tuna is chunks. Therefore, quality control of

imported frozen loins is relatively easy when com-

pared to solid packs. The import duty of frozen tuna

loins is 0%, the same as that for frozen whole tuna

imports. Developing countries, especially those in the

South Pacific should closely watch developments in

loining technology, as this might provide a good op-

portunity to obtain a better yield from their resources.

See also: Canning: Principles; Fish: Processing; Fish

Farming