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

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the market that were not common previously for

the local population feeding habits or were even

relatively unknown.

0002 Fish (bony fish and elasmobranch fish) represent a

large amount of marine-origin meals for direct human

consumption and support a wide series of transform-

ation techniques for subproducts or by-catch such as

oil, flour, protein, and concentrates production.

Fish and Nutrition

0003 For many centuries, fish has been one of our main

foods and at present supplies almost 10% of the

animal-origin proteins eaten at mealtimes; this pro-

portion is much higher in developing countries, where

fish may be the only source of animal protein. Japan,

Norway, Iceland, Spain, and the UK are examples

where fish, fishing, and aquaculture play an import-

ant role within the population’s socioeconomic and

feeding activities (Tables 1 and 2).

0004It is possible to divide fish into two large groups

according to the forms of feeding advantage: primary

products and secondary or subproducts. The former

include fresh, frozen, smoked, salted, and canned

fish, and the latter include oil, protein concentrates,

and hydrolyzed products.

0005Two different types of fish are traditionally con-

sidered (in this case, exclusively finfish) under the

generic denominations of white and blue fish. The

first includes those species that have a white or

whitish musculature, without the strong presence of

darker-colored lateral muscular fascicles, and corres-

ponds to the group of lean and semifat fish (with a fat

content no more than 1.5 and 8–10%, respectively),

such as cod (Gadus morhua), salmon (Salmo salar),

and hake (Merluccius merluccius). The second type is

characterized by its darker muscular tissue, the pres-

ence of a high degree of vascularization in the lateral

muscular fascicles (Vogt’s musculature, of fundamen-

tal importance on fish swimming in oceanic migrator-

ial species as tunnids), and a high fat content (over

10%), which makes them fatty fish, e.g., the sardine

(Sardina pilchardus), herring (Clupea harengus),

mackerel (Scomber scombrus), and eel (Anguilla

anguilla).

0006However, this distinction between lean, semifat, and

fatty fish should be used with some caution, since

a large number of species, e.g., the sardine (fatty fish)

or hake (semifat fish), can have an enormous range of

seasonal variationin their fat content owing to feeding-

habits variation and sexual-products elaboration.

0007The food industry supplies a wide range of different

fish types and products (finfish, shellfish-molluscs,

tbl0001 Table 1 World fish catch (1975–1986)

1975 1980 1984 1985 1986

Composition (10

tonnes)

Finfish 60.5 63.5 73.4 75.8 81.2

Crustaceans 2.1 3.3 3.3 3.5 3.9

Molluscs 3.8 5.2 6.1 6.3 5.4

To t a l c a t c h 66.4 72.0 82.8 85.6 91.5

Hunted (%) 93.0 90.0 87.7

Farmed (%) 7.0 10.0 12.3

Disposition

Human consumption (%) 70.4 73.8 71.9 70.7 70.5

Of which, percentage consumed as

Fresh 38.9 27.3 25.6 25.9 28.3

Frozen 25.3 30.6 34.0 33.6 33.2

Cured 16.7 21.8 20.8 21.5 20.8

Canned 19.1 20.3 19.6 19.0 17.6

Data from Hillcoat JB (1990) Fish farming. In: Somogyi JC and Ho

tzel D

(eds) Marine Foods. Lebbensmittel aus dem Meer, pp. 10–21. Basel: Karger

with permission.

tbl0002 Table 2 Production and use of world fisheries (millions of tonnes)

Pro duction 19 9 0 19 92 19 9 4 19 95 19 9 6 19 97

Continental fisheries

Aquaculture 8.17 9.39 12.11 13.86 15.61 17.13

Catch 6.59 6.25 6.91 7.38 7.55 7.70

Total 14.76 15.64 19.02 21.24 23.16 24.83

Marine fisheries

Aquaculture 4.96 6.13 8.67 10.42 10.78 11.14

Catch 79.29 79.95 85.77 85.62 87.07 86.03

Total 84.25 86.08 94.44 96.04 97.85 97.17

Total aquaculture 13.13 15.52 20.77 24.28 26.38 28.27

Total catch 85.88 86.21 92.68 93.00 94.63 93.73

Total fisheries 99.01 101.73 113.46 117.28 121.01 122.00

Use

Human consumption 70.82 72.43 79.99 84.69 90.62 92.50

Reduction 28.19 29.29 33.47 30.78 30.39 29.50

Preliminary estimation.

Data from FAO (1999) EI estado mundial de la Pesca y la Acuicultura 1998. Versio

n en espan

ol. Parte 1, pp. 1–18. Rome: FAO with permission.

2418 FISH/Fish as Food

shellfish-crustaceans), both catch and aquaculture

production, and marine, salty, or continental in origin:

0008 fresh and cold storage fish;

0009 frozen fish;

0010 dried fish;

0011 salted fish;

0012 smoked fish;

0013 conserved fish (canned or tinned fish);

0014 semiconserved fish (canned or tinned not pasteur-

ized);

0015 Japanese traditional products (Neriseihin) as sur-

imi and kamaboko;

0016 krill (euphausiids);

0017 trepang (dried sea cucumber);

0018 fish oils;

0019 fish flour and meal;

0020 hydrolyzed fish (siloed fish);

0021 fish protein concentrate.

0022 Cold-temperature preservation can be achieved

through a wide range of systems, from refrigeration

by simple addition of ice to cryogenic ultrafreezing.

Preservation may be increased by storage in modified-

atmosphere conditions, ionization and vacuum pack-

aging. Some species require special conditions for

freezing such as sardine (superficial freezing: super-

chilling), tuna (brining solution of calcium chloride),

or shrimp and prawn (brining solution of sodium

chloride with sugar adding).

0023 Refrigeration can be carried out by three different

methods: cold sea water (CSW), refrigerated sea

water (RSW) or a combined method of CSW/ice or

RSW/ice, with or without the addition of antibiotics

to water and ice. Freezing is based on very cold air

flow, surface–plate contact and brining solutions

(euthectic solutions), although air flow and cryogen-

ics are the best techniques. All of these cold-freezing

systems can be adapted for two different purposes:

maintenance of a high-quality product along a

determined, specific short time, or obtaining an

acceptable quality in the long term.

0024 Dried, salted, and smoked fish are short-term

edibles in which only water loss and salt concentra-

tion ensure preservation, smoked fish being more

durable due to semi-cooking of meal and adsorption

of some preservative salts from wood (as tanines)

during the smoking process.

0025 The differences between packed fish (jarred,

canned, tinned, etc.), conserves and semiconserves

depend on the heat used first to prevent microbial

spoilage (sterilization of cans involves the use of tem-

peratures up to 105



C for 30 min). Anchovies in olive

oil is a good example of a tinned fish semiconserve,

as fish fillets are salt-pressed and oil-soaked, but no

sterilization is carried out after canning.

0026Neriseihin products, such as surimi and kamaboko,

are a very important world-wide market, as they form

the basis for a few new marine preparation foods as

cheap sustitutives of more expensive natural meals:

‘lobster tail,’‘crab sticks,’ and ‘young eels’ are

popular products.

0027Fish oils, flours, meals, hydrolyzed solutions and

protein concentrates may be obtained from specific

fisheries (Peruvian anchoveta (Engraulis ringens)) or

as subproduct or bycatch of other principal catches.

Ecuadorian and Peruvian flours, which are used for

production of aquaculture feed, show fundamental

differences in general characteristics (high quality

and low cost) compared with European flours, as

the latter product is a result of damaged specimens

discharged for human consumption, or specimens of

no commercial interest by primary demand, all with a

low-quality composition and similar cost to that of

the Peruvian and Ecuadorian counterparts.

0028Other types of seafood (and continental water

species) should be mentioned, although their import-

ance is local or anecdotal, for example, sea urchins

(genera Echinus, Paracentrotus, Sphaerechinus). A

few species are traditionally caught and consumed

in Spain and France, thus increasing demand and

initiating the introduction of specific aquaculture

industries, which produce both fresh specimens for

direct consumption and manufactured products com-

mercially denominated ‘sea urchin caviar,’ presented

as jarred or tinned semiconserves.

0029Among all these food sources, the krill fisheries that

exploit different species of the genus Euphausia, Thy-

sanoessa, Meganictiphanes,andNictiphanes, with a

total catch of 160 000 tonnes in 1996, are good

examples of a new component of human nutrition

and aquaculture feed, although their fundamental

role in the marine trophic systems must take total

catch quotas under strict controlled management.

General Chemical Composition

0030From a nutritive point of view, the most interesting

chemical components of fish (comprising finfish, ceph-

alopods, shellfish-molluscs and shellfish-crustaceans)

are proteins and fats (Tables 3–5 and Figure 1), as

well as water, which can constitute 70–80% of the

total composition, mineral salts (usually refered to as

ash), and vitamins. Carbohydrates and fiber are

practically nil in fish.

Proteins and Nonprotein Nitrogen Substances

0031The value of fish proteins is very high. It is better than

meat protein and, although inferior to milk and egg

protein, has a stable composition of essential amino

acids, with slight deficiencies of methionine and

FISH/Fish as Food 2419

threonine, and an excess of lysine – very important if

we take into account the fact that this latter amino

acid is lacking in cereals.

0032The protein content of a species depends on many

biological and environmental circumstances (sex,

age, sexual maturity, nutritive conditions, etc.); this

variation can be rhythmic, periodic, or nonperiodic.

Finfish can show a wide range of variation between

10 and 30% in wet weight.

0033The biological coefficient value of protein (B

)

compares retained nitrogen (N

) with gastrointestinal

absorbed nitrogen (N

¼ N

 100:

0034Nonprotein nitrogenous substances are important

in the taste of the fish, with the highest concentrations

being found in migrant and elasmobranch fish. The

nitrogenous substances are mainly free amino acids,

peptides, purine bases, urea and trimethylamine oxide.

Fats

0035Fats are mainly composed of unsaturated fatty

acids, including oleic acid (18:1n-9) and high unsat-

urated fatty acids such as linoleic acid (18:2n-6) and

linolenic acid (18:3n-3), among others. These have an

tbl0003 Table 3 Composition of several seafoods

Protein

(gper100 g)

Fat

(gper100 g)

Energy

(kJper 100 g)

Fat fish 18–23 3–23 420–1260

Lean fish 16–29 <1 294–336

Clam 10.70 0.50 198

Mussel 10.80 1.90 282

Scallop 19 0.90 352

Oyster 10.20 1.40 297

Squid 17 1.30 341

Octopus 10.60 1.00 239

Lobster 15–20 0.5–2.5 294–320

Norway lobster 15.00 0.70 278

Crab 19.50 5.10 518

Prawn 21.00 1.30 400

Sardine 23 13.8 672–1176

Mackerel 23 17.3 756–1302

Tuna 28 8.0 609–1680

Gilthead seabream 17.00 2.70 386

Cod 17.70 0.40 311

Hake 11.80 1.80 266

Turbot 16.10 3.60 425

Adapted from Deslypere JP (1990) Effect of fish consumption compared to

intake of fish oil. In: Somogyi JC and Ho

tzel D (eds) Marine Foods.

Lebbensmittel aus dem Meer, pp. 10–21. Basel: Karger, with permission.

tbl0005 Table 5 Composition of some seafish from the Canary Islands

(central-eastern Atlantic)

Species Proteins

(gper100 g)

Fats

(gper100 g)

Minerals

(gper100 g)

Sardine 14.92 12.79 3.68

Round sardinella 16.28 9.13 3.47

Chub mackerel 15.72 6.73 4.41

Blacktail comber 12.67 1.70 6.73

Large-eye dentex 12.11 3.30 7.38

Common pandora 13.34 2.82 4.30

Axillary sea bream 12.50 2.25 5.46

Bogue 15.41 9.39 4.41

Salema 12.69 2.17 3.40

Parrotfish 12.11 1.62 4.30

Data from Lozano G, Ros MM, Quintero ME, Balguerı

as E and Lozano F

(1987) Consideraciones alimentarias en especies de peces de consumo

comu

n en las Islas Canarias. Alimentaria 180: 47–56.

tbl0004 Table 4 Composition of several transformed seafoods

Proteins

(gper

10 0 g)

Fats

(gper

10 0 g)

Energy

(kJper

10 0 g)

Canned tuna (olive oil) 23 13 874

Smoked salmon 21.50 9.30 710

Canned sardine (olive oil) 22 16.2 977

Fish protein concentrate A *75 1 1292

Fish protein concentrate B *75 10 1630

Fish flour *65 *8 1350

Data from Mataix-Verdu

J and Man

as-Almendros M (eds) (1998) Ta b la s d e

Composici

n de Alimentos Espaoles, 3rd edn. Granada, Spain: Editorial de

la Universidad de Granada and Lozano (not published) with permission.

Ashes

2.3%

Bony fish

Deep-sea sharks

Proteins

17.3%

Fats

1.6%

Humidity

78.8%

Ashes

0.9%

Proteins

23.8%

Fats

0.3%

Humidity

75.0%

fig0001Figure 1 Mean percentage values of proteins, fats, humidity

and ashes of several bony fish (top) and elasmobranch fish

(deep-sea sharks) (bottom) of normal human consumption in

the Canary Islands. Data from Hardisson A, Ba

ez A, Pascual P

and Lozano G (1997) Trace metal content in deep-water sharks

from the Canarian seawaters. J. Vet. Pharmacol. Therap. 20(1):

283–284.

2420 FISH/Fish as Food

important role in the control of blood cholesterol

levels and in the prevention of cardiovascular

problems of arteriosclerotic origin. This is an im-

portant feature in the case of blue fish, such as sar-

dine, anchovy (Engraulis encrasicolus), herring and

bluefin tuna (Thunnus thynnus), as well as other

species of pelagic fish. As in the case of proteins, fats

undergo high seasonal variations in their content, in

this case related to trophic and genetic periods and

migrations.

0036 Recent studies show increasing interest in deep-sea

shark fisheries because of the high levels of unsatur-

ated hydrocarbon compounds in shark liver oils.

Squalene (C

) and the hydrogenated form squa-

lane (C

) play an important role as lubricants

and emolients and as a base for a range of products

in the pharmaceutical and cosmetic industries, be-

cause they help through-the-skin absorption and

avoid water loss.

Carbohydrates

0037 Carbohydrate concentrations are very low

(0.1–1%) in fish, and their contribution to the diet

is insignificant.

Vitamins

0038 Fish is a rich source of fat-soluble vitamins, such as

vitamins A and D. In lean fish, they are found almost

exclusively in hepatic oils (the best example being

cod liver oil), but in the case of fatty fish, they are

also present at high levels in muscular tissues. Vita-

mins B

,andB

, and nicotinamide are also found

in significant proportions in the liver and gonads.

Minerals and Heavy Metals

0039 Fish contain many important minerals, mainly

located in the viscera, muscles, and bones. Among

the most abundant elements are sodium, potassium,

calcium, iron, chloride, phosphate, sulfate and iodine.

Iodine is very important in the treatment of illnesses

caused by the malfunction of the thyroid gland, which

can cause delays in growth and/or dwarfism.

0040 In terms of the alimentary structure of fish, the

heavy metal content present in the edible parts is an

important factor because of the toxic characteristics

of these cations and their slow accumulation in

the organisms of the trophic chain by bioaccumula-

tion or biological amplification (Table 6). Mercury,

lead, tin, cadmium, and vanadium are particularly

important heavy metals and are regulated, as far as

the maximum total content permitted for consump-

tion, acceptable daily intake, etc., are concerned, by

the World Health Organization and national organ-

izations working together on health problems.

Digestibility

0041A significant advantage of fish as a food is its easy

digestibility, which results from the special configur-

ation of the muscular structures. These are composed

of short muscular segments (myotomes) separated by

conjunctive covers (myosepts), which together pro-

duce short muscular fibers. Myosepts are more easily

transformed to gelatines at 65–70



C, causing the

destruction of muscular structures, and improved

access to fibers, than in other animal meats.

0042Fatty fish are less digestible than lean fish but pro-

vide more energy to the consumer. With a mean

content of 18–20% protein, fatty fish provide up to

1302 kJ per 100 g, compared with 336 kJ per 100 g in

lean fish. Taking into account losses after removal of

the head and internal organs (up to 50–60% of the

fresh weight), these values are reduced to 357 and

155 kJ per 100 g, respectively.

0043The digestibility coefficient (D

) compares absorbed

nitrogen (N

) with ingested nitrogen (N

) as follows:

¼ N

 100:

0044D

values range from 70% (ray) to 100% (cod and

hake) in finfish, 75–85% in molluscs, and 70–90% in

crustaceans.

Popular Varieties and National

Preferences

0045In general, it is difficult to list the entire range of species

or groups of species that comprise the fishing resources

of a country, region, or specific geographical area,

given the number of variables of differing importance,

such as industrial and small-scale fishing, fleet type and

tbl0006Table 6 Mercury levels in some seafish from the Canary

Islands (central-eastern Atlantic)

Species Mercurylevel (p.p.m., w/w) Samples

Sardine 0.025 Fresh

Round sardinella 0.003 Fresh

Chub mackerel 0.003 Fresh

Blacktail comber 0.004 Fresh

Large-eye dentex 0.006 Fresh

Common pandora 0.003 Fresh

Axillary sea bream 0.005 Fresh

Bogue 0.005 Fresh

Salema 0.004 Fresh

Parrotfish 0.003 Fresh

Tuna 0.234 Canned

Albacore 0.270 Canned

Yellowfin tuna 0.005 Canned

Skipjack 0.082 Canned

Data from Lozano G, Ros MM, Quintero ME, Balguerı

as E and Lozano F

(1987) Consideraciones alimentarias en especies de peces de consumo

comu

n en las Islas Canarias. Alimentaria 180: 47–56.

FISH/Fish as Food 2421

catch methods, the oceanographic and biological char-

acteristics of the environment, migrant and sedentary

species, coastal and oceanic areas, insular systems,

and national and local gastronomic traditions.

0046 The number of variables increases in the case of

nations whose fishing activity includes freshwater

species (in the strict sense of the term, or combining

marine and freshwater characteristics) and which can

boast aquaculture potential in one or many of its

varied forms. The situation in such cases is clearly

complex when it comes to handling data concerning

catches, fishing effort, and production.

0047 Denmark’s fishing and production are based on

gadoids, pleuronectids, clupeids, and scombrids;

Australia’s on lobsters, crabs, tuna-like fishand sharks;

Uruguay’s on squids and hake (Merluccius spp.); Mex-

ico’s on lobsters, scombrids, anchovy (Engraulis ring-

ens) and sardine (Sardinops sp.); Japan’s on scombrids

and lobsters (with, in this case, considerable aquacul-

ture production); and Norway and Greenland’son

salmonids and gadoids; USA’s on salmonids, cyprinids,

anguilids, clupeids, gadoids and scombrids (although

one should not overlook the importance of shark-fish-

ing in the deep waters of the Pacific coast); Germany’s

on salmonids, cyprinids, anguilids, clupeids, gadoids,

and scombrids; the UK’s on gadoids, merlucids, clu-

peids, flat fish, and salmonids; and Spain’s on, among

others, anguilids, cyprinids, salmonids, scombrids,

sparids, gadoids, merlucids, flat fish, cephalopods,

and crustaceans (Table 7).

Preferences for Lean, Semifatty, and

Fatty Species

0048Local preferences for a particular type of fish (lean,

semifatty, or fatty) depend on many factors. Some of

these are seasonal and biological (catching species on

a massive scale as they migrate during a given period,

presence near areas of reproduction, disappearance

and replacement of species), whereas others have

more to do with traditions and culture (consumption

of a species during a short period, even though it is

present in the fishing zone for all or part of the annual

cycle) or social, economic, and political consider-

ations (moving to other fishing grounds, changes in

selling price, employment complications in the sector,

the imposition of reduced catch quotas, etc.).

0049In the western Mediterranean countries (Spain, for

example), species of white fish (lean and semifatty)

are consumed throughout the year, whereas the

greatest consumption of blue fish is in the summer,

the most important species being bluefin tuna (Thun-

nus thynnus), bonito (Sarda sarda), skipjack (Katsu-

wonus pelamis), albacore (Thunnus alalunga) and

yellowfin tuna (Thunnus albacares). In winter, the

mainstays are mackerel (Scomber scombrus), chub

mackerel (Scomber japonicus), sardine (Sardina pil-

chardus) and anchovy (Engraulis encrasicolus). The

same is true, to a large extent, of other neighboring

Mediterranean (France and Italy) and Atlantic areas

(Portugal).

0050This pattern is also seen clearly in the Canary

Islands (central-eastern Atlantic), where multispecific

small-scale fishing is practiced for white fish and

crustaceans (demersal species) between October and

April, whereas during the period May to September,

activity centers almost exclusively on bluefin tuna,

skipjack, albacore, bigeye (Thunnus obesus) and

yellowfin tuna (pelagic species), which are also

caught by large Russian, Korean, and Japanese fleets.

0051Turkey deserves special mention, since, despite its

extensive scombrids, clupeids and flat fish resources,

it is not a fish-consuming country. In spite of strenous

efforts by the government, the traditional cultural

situation has remained unchanged. Thus, an ex-

tremely important source of food, for both internal

consumption and export earnings, is still untapped

because Turkey is not a fishing nation.

Usage of Marine versus Freshwater

Species

0052As mentioned earlier, the harnessing and use of

marine or freshwater species depends on a wide

range of circumstances, most notably, in the case of

freshwater fish, the presence of rivers, lagoons, and

tbl0007 Table 7 Marine and freshwater species of fish normally

consumed in Western Europe

Species Marine Freshwater

Sturgeon þ

Sardine þ1

Herring þ1

Anchovy þ1

Salmon þ

Trout þ

Northern pike þ

Tench þ

Carp þ

Eel þ

Cod þ2

Hake þ2

Mackerel þ1

Tuna þ1

Skipjack þ1

Turbot þ2

Plaice þ2

Sole þ2

Freshwater genetic areas.

Marine genetic areas.

þ1, Pelagic fish; þ2, demersal fish (ground fish).

Data from Lozano G and Hardisson A (1993) Fish as food. In: Macrae R,

Robinson RK and Sadler MJ (eds) Encyclopaedia of Food Science, Food

Technology and Nutrition, vol. III, pp. 1834–1838.

2422 FISH/Fish as Food

lakes in the fishing area. This enables the resource to

be extracted and distributed without any great diffi-

culty, given that, for the most part, marketing of this

type of fish tends to be limited and is almost never

exported.

0053 Nevertheless, both manufactured products (par-

ticularly smoked fish) and species, which are pro-

duced by means of aquaculture, are opening up new

markets for freshwater fish in countries, or regions,

where previously they had been rejected or unknown,

and where consumption was practically nil.

0054 Manufactured products are derived from eel,

sturgeon (Acipenser sturio), salmon and trout

(Salmo spp.), and, in the case of aquaculture species,

tilapia (Tilapia spp.), tench (Tinca tinca), carp (Cypri-

nus spp.), salmon and trout. All of these form part

of a sizeable range of widely distributed and

economically important species.

0055 The most important characteristic of aquaculture is

its capability of producing high-quality edibles, both

nutritional and health properties at an almost con-

stant market price, irrespective of seasonal or socio-

economic situations or politics (migrations, weather

condition, political restriction to foreign fleets to

fishing in national fishing grounds, bans owing to

biological reasons, total allowable catches).

0056 Of special significance is the controlled addition of

modified diets to species in order to increase their

growing rates, condition factor, and certain biological

characteristics (e.g. resistance against diseases), thus

creating an improved food for human consumption.

Components such as folic acid, ascorbic acid, and

l-carnitine are being used in new types of foods.

0057 In the EU member states, all production (marine

and continental) is regulated under the ‘Sectorial

Program of Coastal Fisheries and Aquaculture’ that

assures management, assessment, market procedures,

and scientific aid in quinquennial programs. Some

species that were not accessible via aquaculture a

few years ago are now being consumed in great

quantities. For example, turbot (Scophthalmus max-

imus) has seen an extraordinary increment in produc-

tion to 10 000 tonnes in 1999 (4400 tonnes in Spain

alone).

Problems of Supply and Demand

0058 The complex nature of the various sectors of the

fishing industry, catches, distribution, processing,

and marketing, can be explained by a series of factors.

In some cases, a small number of species are fished for

a particular type of industry (e.g. canning or smoking

factories), or in order to supply a traditional and

unchanging market requiring a constant level of

quality catches throughout clearly defined periods.

0059These circumstances may vary considerably as a

result of resource modifications produced by natural

or artificial causes (variations in the environment,

changes in the recruitment rate, overfishing) or

by changes in eating habits (varying in demand caused

by the introduction of species produced through aqua-

culture, or caught in areas previously not fished by the

fleet). Such species displace or at the very least com-

pete commercially with those that are traditionally

consumed. The crises affecting the anchoveta in Peru

(only 200 000 tonnes caught in 1985), cod in Green-

land (7000 tonnes in 1986), the demise of the Euro-

pean herring, or the Saharan Bank sparids, are prime

examples of resource modifications, whereas cases of

aquaculture include the introduction of salmon, trout,

tench, and eel farming in Spain.

See also: Fish: Introduction; Catching and Handling; Fish

as Food; Demersal Species of Temperate Climates;

Pelagic Species of Temperate Climates; Tuna and Tuna-

like Fish of Tropical Climates; Demersal Species of

Tropical Climates; Pelagic Species of Tropical Climates;

Important Elasmobranch Species; Processing; Dietary

Importance of Fish and Shellfish; Fish Farming

Further Reading

Bligh EG (1990) Seafood Science and Technology. Oxford:

Fishing News Books.

Brito G, Dı

az C, Hardisson A and Lozano G (1994) Con-

centrations of Mercury in fresh and salted marine fish

from the Canary Islands. Journal of Food Protection 57:

246–248.

Connell JJ (1995) Control of Fish Quality, 4th edn. Oxford:

Fishing News Books.

FAO (1999) El estado mundial de la Pesca y la Acuicultura

1998. Versio

n en espan

ol. Parte 1, pp. 1–18. Rome:

FAO.

Hardisson A, Ba

ez A, Gonza

lez T, Pascual P and Lozano G

(1997) Trace metal content in deep-water sharks from

the canarian seawaters. Journal of Veterinary Pharma-

cology and Therapeutics 20: 283–284.

Lozano G, Ros MM, Quintero ME, Balguerı

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FISH/Fish as Food 2423

Demersal 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), Maharashtra, India

N V Chavan, Adarsha College, Hingoli, Maharashtra,

India

Background

0001 Fishes of many families, shapes, and sizes obtain

their food in the near-bottom zone and show morpho-

logical and behavioral adaptations for life on or

near the seabed. These are the demersal fishes, com-

prising both benthic and benthopelagic species, the

latter usually performing vertical migrations to

feed. Demersal fishes occur at all depths and in all

near-bottom habitats of the oceans. In this article,

emphasis is given on demersal species such as cod,

haddock, plaice, and sole, which live on or near the

bottom of the sea; the continental shelves along

the coasts of Europe, Greenland, Iceland, and North

America. Worldwide, about 85% of the total contin-

ental shelf area has sandy or muddy substrate. Only

about 6% is rocky or gravelly, and the remain-

ing areas are coral reefs or shell beds. However,

there are both latitudinal and depth-related patterns.

Corals are almost entirely confined to low latitudes

where organically enriched muddy areas are also

most extensive, particularly near the mouths of

major rivers or below highly productive upwelling

areas. Sandy, rocky, and gravelly sediments are more

common at high latitudes. Regional and local modifi-

cations of the distribution and character of soft

sediments are common as a result of water currents

flushing the shelves. In addition to offering a range of

physical habitats to fishes, continental shelves are

usually highly productive, and especially in temperate

and boreal regions, demersal species of the shelf

waters are very abundant and support some of the

world’s major fisheries. Of the approximately 13 500

marine fish species, 1000–2000 species inhabit con-

tinental shelf-water of temperate zones. The majority

of these are demersal species.

Taxonomic Diversity, Geographical

Patterns, and Assemblages

0002 A wide range of families, including both cartilaginous

and bony fishes, have demersal representatives in

shelf-waters. There are several rather consistent

geographical patterns, however, on both a worldwide

and regional scale. The abundance and biomass of

demersal fish are considerably higher at high lati-

tudes, i.e., in temperate climates, normally due to

the high abundance of a few species, especially

gadiform fishes such as hakes (Merluccidae) and

cod-like fishes (Gadidae), but also flatfishes (Pleuro-

nectiformes) and rockfishes belonging to Scorpaeni-

dae (Figure 1). Predominant differences between the

oceans have evolved, the gadiform fishes being more

diverse on temperate Atlantic shelves than on North

Pacific shelves, where scorpaenids are very diverse

and few gadiforms occur. Narrow shelves tend to

have fewer demersal species than wide shelves and

shelf seas. The highly productive upwelling areas as-

sociated with eastern boundary currents have few

demersal species, and most are benthopelagic.

Hakes are very well adapted to these environments

and live both demersally and pelagically, mainly feed-

ing on other fish.

Adaptations of Demersal Fishes

0003One adaptation apparent in demersal species is in

response to the vertical gradient in light intensity.

Many species can adjust their body coloration to

their environment almost continuously, while some

species like Atlantic cod (Gadus morhua) have differ-

ent persistent color varieties depending on the habitat

in which they grow up and live. Most shelf and upper

slope fishes are countershaded. They have dark backs

to reflect enough of the strong downwelling light to

match the dim upward component of the ambient

light, with silvery flanks to mirror the background

from all visible angles. However, bright sunlight in

the clearest oceanic waters penetrates to only 1000 m

or so, and inturbid slope waters, penetration is reduced

to considerably less than this. Therefore, the great bulk

of the ocean is unlit by the sun, resulting in a reduction

in countershading for protection, often accompanied

by anoverall darkening in body colour, with increase in

the living depth of the species. Because the red end of

the spectrum is most readily absorbed by sea water,

darkening of the body at depth can be achieved either

by black or by red pigmentation. Most demersal

species tend to be blackish, but striking examples of

red camouflage are found in the orange roughy,

Hoplostethus atlanticus, and in Sebastes species. The

rapidly diminishing intensity of light with depth in the

ocean has resulted in the refinement of a range of

sensory systems in demersal bottom fishes. Surpris-

ingly, there is no general trend towards a reduction in

eye size as occurs in pelagic fishes.

0004Unlike the pelagic fishes, which are slender and

often torpedo-shaped, the typical demersal fishes are

2424 FISH/Demersal Species of Temperate Climates

not so well adapted in terms of body shapes or physi-

ology for prolonged fast swimming. However, many

shapes ranging from an eel shape to the more classical

fish shapes of the cod, sparids, and rockfishes have

proven successful (Figure 1). Regulating buoyancy

may not be as important to demersal fish as to pelagic

organisms. Demersal fish species come in all sizes

from small gobies, reaching a length of only a few

centimeters, to the Atlantic halibut (Hippoglossus

hippoglossus) and Greenland shark (Somniosus

Rajidae

Squalidae

Congridae

Scorpaenidae

Scyliorhinidae

Lophiidae

Soleidae

Sparidae

Anarhichadidae

Gobiidae

Ammodytidae

Merlucciidae

Gadidae

fig0001 Figure 1 Body shapes of fish from selected demersal families.

FISH/Demersal Species of Temperate Climates 2425

microcephalus), which may reach 2 and 6.5 m in

length, respectively. Many modes of life are possible

in the demersal environment. Some fishes are sluggish

and have evolved a typical ‘lie-and-wait’ strategy,

while others are very active, and some almost behave

as pelagic species. Flatfishes and several rays spend

part of their time buried in the sand and may only

emerge for certain times of the day or tidal cycle to

feed. Most of the demersal species are more active

during the night or at dusk and dawn. Camouflage

may be attained in many ways, i.e., through body

shape, skin coloration, and modification of skin into

the appendages resembling algae or debris. The reten-

tion of functional and substantial eyes, together with

specialized adaptations, must surely be in response to

the widespread phenomenon of the biological light,

which is produced by very many organisms in the

deep sea, including those associated with the sea

floor. In contrast to the pelagic oceanic fishes, rela-

tively few deep-sea demersal fishes have evolved elab-

orate light-organ systems of their own. For example,

there is no need for ventral camouflage in bottom

dwellers or bioluminescent lures in a habitat at the

sediment–water interface where food ultimately col-

lects and is thus found more easily simply by foraging.

Feeding and Diets of Demersal Fishes

0005 Most of the demersal species of temperate region are

carnivores, customarily grouped into three categor-

ies, piscivores, benthophages, and zooplanktivores,

that predominantly eat fish, benthos, and zooplank-

ton, respectively. Many demersal fishes depend on

pelagic production by feeding on vertically migrating

nekton and zooplankton entering or inhabiting the

near-bottom layer. Piscivores usually have the cap-

acity to deal with live prey that are large compared

with their own body size, and so they tend to have

large gapes. Some swallow their prey whole, and

others tear and bite the prey into smaller pieces.

However, the techniques vary widely between species

within the demersal fish group. Piscivores generally

have several rows of conical backwardly pointing

teeth both on the jaws and within the mouth and

pharynx. These primarily prevent the prey from es-

caping and aid swallowing. Benthophagous fishes

also have several prey capture methods. Some apply

suction after detecting prey on the surface of the

sediment or within the sediment, and others bite off

the siphons of buried bivalves. Others feed on shelled

animals and have strong, muscular jaws. Zooplankti-

vores often lack dentition on the jaws and rely on

suction for ingesting their rather small prey whole.

Most species probably pick their prey one at a time

rather than filter-feed as clupeids and mackerels do at

high prey densities. In most demersal species, there

are significant ontogenetic changes in diet and feeding

ranges. At metamorphosis, when larval characters are

lost, and most demersal fish take up a demersal life

style, pronounced diet changes from feeding on

planktonic crustaceans to feeding on benthic or

benthopelagic prey may occur. As a fish grows in

size, larger or more energy-rich prey are needed to

satisfy its energy requirements. Many species there-

fore go through a succession of feeding modes during

their lifetime, usually starting as planktivores and

ending as piscivores or benthofages. For a given

species, pronounced diet shifts tend to occur at rather

fixed sizes, but habitat shifts may happen concur-

rently, and it is sometimes difficult to determine

which is more significant. Many species are quite

opportunistic, and their diet varies greatly between

habitats and seasons, often depending on the food

availability.

Major Demersal Species

0006The major species of demersal species include the

Gadiformes or cod-like fish (sometimes called the

Anacathini – fish without spines). These include

commercially valuable species like the cod (Gadus

morhua), haddock (Melanogrammus aeglefinus),

ling (Molva molva), and whiting (Merlangius merlan-

gus).

Cod

0007The cod belongs to the family, the Gadidae (genus

Gadus), represented by at least 19 species in the de-

mersal habitats. They can be distinguished from other

genera in the family by having three dorsal and two

anal fins. There are 10 species, of which six possess a

barbell, a sensory process that hangs down, or may be

extended forwards, from the lower lip. In four of

these species, the upper jaw is larger than the lower

jaw: the cod, Gadus callarias, green–yellow with a

number of dark spots and a white lateral line; the

haddock, G. aeglefinus, gray with a prominent

black blotch on the shoulder and a black lateral

line; the bib or pout, G. luscus, very deep in the

body and copper-colored, with some dark irregular

bands, and the poor cod, G. minutus, similar to the

last, but smaller and not so deep in shape and brown-

ish yellow with no bands. Then there are the two

species that have a barbell but whose lower jaw is

larger than the upper jaw: the coal-fish or saithe,

G. virens, with very dark skin on top, almost black,

but a white lateral line and the teeth in the upper jaw

all about the same size; and the pollack-whiting,

G. esmarkii, with the teeth on the outer margin of

2426 FISH/Demersal Species of Temperate Climates

the upper jaw stronger than the others; this is a small

fish with a beautiful golden color. The geneva that

have no barbell include the whiting, G. merlangus,

with silvery sides and a black spot at the root of the

pectoral fins and the pollack, G. pollachius, dull

green with a lower jaw longer than the upper jaw,

the blue whiting, G. poutassou, which is like a

whiting, but has a very long first anal fin and is

smaller; and the silvery cod, Gadiculus argenteus,

which lives in deep water over the edge of the contin-

ental shelf. The cod is undoubtedly the most import-

ant demersal food fish of our seas, and not only

around the British Isles, but in the Arctic waters of

Iceland, northern Norway, and Bear Island.

0008 A large cod may produce as many as four million

eggs at one spawning. All members of this family

lay floating eggs; their small transparent spheres

then drift with the moving waters and develop into

the young fry. The spawning period is February to

April, and the principal areas are those of the Great

Fisher and Ling Banks, and Long Forties and Flam-

borough grounds. These have been determined by the

charting of eggs and fry caught in plankton nets and

from the landings of ripe and spawning fish. The fry,

which are only 6 mm long when they hatch, spend

about 2.5 months as part of the plankton, and are

subject to the same hazards of shortage of food or

excessive abundance of predators as the young of

other species. They feed almost entirely upon the

small crustaceans (copepods) of the plankton. During

this period, circulating currents keep them within the

North Sea, and when they are just over 2 cm long,

they seek the bottom. Once on the sea-bed, they are

extremely difficult to catch, especially as the nursery

regions contain a good deal of rough ground. Still

feeding upon crustacea, but now the bottom-living

amphipods, isopods, and small crabs, the young cod

grow quickly on the typical nursery grounds and

begin to be caught by the commercial trawlers when

they are 1.5–2 years old and 30 to 36 cm length; in

some deeper regions of the North Sea, however,

growth is slower, and they may not enter the fishery

until they are 3 years old. The age of a cod is generally

determined from its scales and not its otolith. Cod do

not begin breeding until they are about 5 years old

and have reached a length of some 69 cm.

0009 Adult cod feed mainly upon fish, particularly her-

ring, mackerel, small haddock, and sand eels; they

also take mollusks, crustaceans, and bristle worms

to a lesser extent. There is a marked contrast between

the feeding of the cod and that of its close relative,

the haddock. This is interesting in view of the well-

established rule that two closely allied species cannot

remain competing with one another in the same habi-

tat: one, if slightly the more efficient, will certainly

eliminate the other. The cod and haddock exist to-

gether on the same grounds but have distinctly differ-

ent food preferences. Whereas the cod feeds mainly

on fish, the haddock, except for sand eels, feeds

almost entirely upon invertebrates: bristle worms,

crustacea, mollusks, and particularly brittlestars,

and small sea urchins. The haddock food is limited

to rather small slow-moving animals found close to,

or burrowing in, the bottom. Cod and hake eat larger

and more quickly moving animals, even considering

only fish of a comparable size. The nature of

the mouths of these three species is significant. The

mouths of hake and cod are much larger than those of

haddock and practically, if not absolutely, terminal.

They are provided with sharp teeth, and all the

mouthparts are strong. Haddock, however, have a

small mouth positioned somewhat ventrally. Their

mouthparts are soft, and the teeth are ordinarily

dull. They are, however, provided with better-

developed muscular lips. Cod and hake are well

equipped for capturing large or fast-moving objects,

but haddock, with their smaller, ventrally positioned

mouths, are best equipped for picking small animals

off or out of the bottom. In addition, the heaviest

built portion of the haddock is the anterior part of

the body, and this may help them to remain more

easily in a forwardly tilted position while feeding.

Haddock

0010The haddock is perhaps commercially second in im-

portance to the cod among the trawl-caught fish. It is

very abundant in the North Sea, particularly in the

northern half, and further north to the Faeroes, Ice-

land, and the Barents Sea, but it does not go as far

north towards Spitsbergen as does the cod. On the

western side of the Atlantic, the haddock is also

abundant on the coastal banks from Cape Cod to

the Cabot Strait, and large concentrations are found

on the southern hald of Grand Banks of Newfound-

land. The main spawning period of haddock, like that

of cod, is from February to April. The haddock is

smaller than the cod, becomes mature much earlier,

when only 2 years old, and is less prolific. A 2-year-

old fish of about 25 cm in length will produce some

30 000 eggs, a 3-year-old (30 cm long) some 100 000,

and a 6-year-old (only about 40 cm long) some

280 000. Haddock in the trade category ‘extra

large,’ i.e., over 152 cm in length, are rare today;

occasionally, however, much larger ‘jumbos’ are

caught. For both cod and haddock, there is quite a

marked difference in the growth rates of fish from the

northern and southern halves of the North Sea. In

the north, a 5-year-old haddock will have an average

length of only 32 cm, whereas in the south, a haddock

FISH/Demersal Species of Temperate Climates 2427