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

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Demersal Species of Tropical

Climates

G D Khedkar and B V Jadhao, Dr Babasaheb

Ambedkar Marathwada University, Aurangabad,

Maharashtra, India

N V Chavan, Adarsha College, Hingoli, Maharashtra,

India

C D Khedkar, College of Dairy Technology, Warud

(Pusad), Maharashtra, India

Introduction

0001 Demersal fishes have been a major source of protein

for people all over the world for thousands of years.

Worldwide, about 85% of the total continental

shelf area has sandy or muddy substrate. Only about

6% is rocky or gravelly, and the remaining 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 or-

ganically enriched muddy areas are also most exten-

sive, particularly near the mouths of major rivers

or below highly productive upwelling areas. Sandy,

rocky, and gravelly sediments are more common

at high latitudes. The tropical waters contain a

greater number and diversity of fish species than

waters of the higher latitudes. Demersal fish of

economic importance are concentrated on the contin-

ental shelf and on the continental slope down to

about 500 m. They live on or near the bottom of the

ocean. A regular landing from a deep-sea trawling

session would include catfish, croakers, soles,

groupers, shinynose, snappers, mullets, and mega-

lops. World catches of demersal species increased

rapidly during the first three-quarters of the 20th

century. Since then the catches from some stocks

have declined, due to overfishing, while other previ-

ously underexploited stocks have increased their

yields (Table 1). The limits of biological production

have probably been reached in many areas. In

order to maintain the fisheries and to protect the

ecosystems which support them, careful management

is needed.

Migration in Demersal Species of Tropical

Climates

0002 Diurnal migrations, either vertically or horizontally,

are common in demersal fishes. More fascinating,

however, are the long-distance seasonal migrations

associated with reproduction, feeding, and sometimes

overwintering. Many examples were already well

described several decades ago, based on traditional

tagging data. But nowadays scientists are employing

the application of modern electronic tagging tech-

niques, whereby perfect positional information can

be derived after retrieval of the tag. The traditional

tagging experiments have provided evidence of

migrations across deep-sea areas. Even transatlantic

crossings have been recorded for cod. Although such

basin-wide migrations may not occur regularly, they

certainly show that demersal fishes are quite capable

of considerable movements over long distances.

Sensory Systems in Demersal Fishes of

Tropical Climates

0003The shelf environment is generally well-lit and most

demersal fishes have well-developed vision. In add-

ition demersal fish may use mechanoreceptors (sense

of pressure, motion, and sound), chemosensory

(olfaction and gustation) and electrosensory (i.e., abil-

ity to detect electric fields) systems. Different systems

may play essential roles during different stages of

important processes such as prey detection, capture

and handling, predator avoidance, or reproduction. In

general, mechanoreception by the acousticolateralis

system (lateral line organ and ear) tends to be most

important for the detection of predators, conspecifics,

and other physical disturbances in the environment.

Olfaction is very important to benthofages that have

to search the substrate for food, whereas planktivores

tbl0001Table 1 Total world catch of major demersal fish species

(1990–2000)

Scientific name Common name Catch

(tonnes)

Ammodytes spp. Sand eels 1 003 343

Ariidae spp. Sea catfish nei 242 815

Cantherhines spp. Filefish 234 446

Elasmobranchii Sharks, skets, rays 337 819

Gadus macrocephalus Pacific cod 425 467

Gadus morhua Atlantic cod 2 317 261

Macruronus magellanicus Patagonian grenadier 230 221

Macruronus novaezelandiae Blue grenadier 255 421

Melanogrammus aeglefinus Haddock 273 459

Merluccius capensis Cape hakes 266 854

Merluccius gayi South Pacific hake 197 911

Merluccius hubbsi Argentine hake 526 573

Micromesistius poutassou Blue whiting 628 918

Nemipterus spp. Threadfin breams 186 201

Pleurogrammus azonus Atka mackerel 237 343

Pleuronectiformes Flatfishes nei 289 551

Pollachius virens Pollock 385 227

Sciaenidae Croakers 492 528

Sebastes spp. Atlantic redfishes 318 383

Theragra chalcogramma Alaska pollock 3 182 645

Trisopterus esmarkii Norway pout 299 145

2438 FISH/Demersal Species of Tropical Climates

and piscivores tend to rely more heavily on vision.

Gustation is most important after capturing prey.

Benthofages may have elaborate adaptations of their

olfactory system. In addition to a well-developed

nose, they may have barbells on the snout (e.g.,

gadids, zoarcids) and modified and extended first

rays of their pectoral fins (e.g., Triglidae) densly

packed with olfactory sensory cells. The electrosen-

sory system is particularly well developed in some

sharks and rays, and they may primarily use this

system for prey location, but also for orientation and

navigation.

Life History Characteristics of the

Demersal Fishes of Tropical Climates

0004 Life history strategies are best examined in the con-

text of the assemblage or community within which

the fish operates. No species lives in isolation, but

interacts with and influences the activities of all the

other species it regularly encounters. Ecological

understanding ultimately grows out of the study of

communities, and this perspective is the one most

deep-ocean ecologists have adopted. Comparative

study of several systems, when possible, can be very

insightful. The samples required for this sort of study,

however, are not easily come by. Large numbers are

required, which, in the best case, should encompass

most life stages and time series over seasons, over

years, and over space. A single sampling gear rarely

suffices, and even a suite of different nets, for

example, might also be complemented with cameras

and other ‘snapshot’ devices. For deep-sea fishes, it is

hard to find any area where such requirements are

met. One that comes somewhat close is in the deep

abyssal region of the eastern Atlantic.

0005 Most demersal teleosts (bony fishes) are oviparous

and produce free-floating eggs. Mating and spawn-

ing happen at the same time, often in mid-water.

Some notable exceptions are the viviparous redfish

(Sebastes) that release numerous pelagic larvae, and

the wolfish (Anarhichadidae) which deposits a cluster

of large eggs that is guarded until hatching. Sand eels

(Ammodytidae) also have demersal eggs but do not

protect the eggs. Most teleosts have no parental care

other than making sure that they mate and spawn

in an area and habitat that enhances the survival

probability of their eggs, larvae, and pelagic juveniles.

Most pelagic teleost eggs are small, i.e., a few

millimeters in diameter, and fecundity is high, i.e.,

thousands to millions of eggs per female. Batch

spawning is common in the highly fecund species,

e.g., cod may spawn 10–13 batches of its very small

eggs within a spawning season.

0006Demersal sharks are either oviparous or vivipar-

ous, whereas rays and chimaeroids are oviparous,

attaching their few large encapsulated eggs to debris

or macroalgae. All species produce rather few young

in each batch, i.e., from a couple to a few tens of eggs/

juveniles, and lifetime production is very low com-

pared with most teleosts. Upon hatching or birth, the

young resembles the adults. Spawning seasons vary in

duration, and the general rule is that the more sea-

sonal the production cycle, the more fixed and limited

is the spawning season. High-latitude fishes and those

living in monsoon or upwelling regions have com-

paratively short spawning seasons, whereas tropical

and subtropical fishes have protracted seasons or

year-round reproduction. Larvae hatched from small

pelagic eggs have a yolk sac that may provide suffi-

cient nutrition for a few days or weeks, after which

they depend on exogenous feeding, usually on small

crustacea such as copopod nauplii. The mortality in

this perod is very high indeed, and only a minute

fraction of the total number of eggs spawned will

eventually result in a surviving demersal juvenile.

The teleost postlarvae pass through metamorphosis

upon reaching a certain size. Characters such as fins

and juvenile pigmentaion develop, and sense organs

also become fully developed. In flatfishes, the eye

migration occurs. In general, the larva is transformed

into a fish which is morphologically and behaviorally

adapted for demersal life. Associated with this change

is the settling on the seabed, at least for parts of the

diurnal cycle. Settling areas are often, but not always,

separated from the feeding areas of the older fish.

This reflects the different habitat and food require-

ments of juveniles and adults, but may also reduce

cannibalism. In the majority of teleost species, the

demersal nursery areas are shallower than feeding

grounds of older conspecifics. Estuaries and offshore

shoals are typical nursery areas, also rocky shores

where the substrate and macroalgae offer protection

and a variety of prey. Tidal flats and sandy beaches

are typical habitats of juvenile flatfish. A gradual

ontogenetic shift in depth distribution happens as

the juveniles grow larger.

0007The expected longevity of demersal species of trop-

ical climates varies greatly. A general pattern is that

longevity increases with increasing adult size, but

there are many exceptions to this rule. Some species,

i.e., redfishes, can probably live for at least 30–40

years, but this is unusual for shelf species. Small

species such as Norway pout may live for 5–6 years

at most, but in exploited areas this seldom happens.

In most shelf waters, the fisheries have influenced

age distributions to the extent that life expectancy is

significantly reduced.

FISH/Demersal Species of Tropical Climates 2439

0008 Somatic growth patterns also vary widely among

demersal fishes of tropical climates. In fast-growing

species living in strongly seasonal environments, the

overall growth trajectory may show seasonality either

because food supply and feeding rates vary, or

because the somatic growth is influenced by repro-

ductive activity/gonad growth. Growth rate usually

declines significantly when the fish becomes mature,

but never ceases entirely. Attempts have been made to

classify species into r- and K-selected types (r and K

are coefficients expressing rate of reproduction and

somatic growth, respectively). The r-selected types

are those with short life spans but fast growth and

rather small adult size. They mature at a small size

and young age, and can rapidly take advantage of

short and unpredictable favorable environmental

conditions by increasing their numbers. The K-

species, however, tend to invest more energy in som-

atic growth by growing more slowly and maturing

later in life, when they are capable of producing many

young. The populations of such species comprise

many age groups, and they are not, like the r-species,

so vulnerable to repeated recruitment failures due to

low survival of young over a range of years. There are

many species that do not readily fit into these classes,

and it is unusual for demersal species of tropical

climates to have the extreme r-orK-strategies seen

among epipelagic fishes and demersal deep-sea fishes,

respectively.

Species Distribution

0009 The vast extent and inaccessibility of the near-bottom

oceanic environment have resulted in extremely

patchy sampling and arguably therefore a quite re-

stricted, and no doubt biased, view of overall demer-

sal fish distribution and community composition.

Slope areas in certain regions, especially some parts

of the North Atlantic, are notable exceptions yet, on

the basis of relative areas, the proportion of the abys-

sal floor of the world ocean that has ever been

trawled is so minuscule that any evenly distributed

species represented in collections by more than 20

specimens in toto is potentially more numerous across

the globe than in humanity! The relative uniformity

of physical features, such as temperature and salinity

at considerable depth, could allow very widespread

distribution patterns to occur. The detailed know-

ledge of the distribution of most of the demersal

species of tropical climates, however, remains

obscure. Such knowledge is largely derived from

taxonomic and rare zoogeographic studies. Rarely

does it come from studies of full assemblages where

species, ecology, and interrelationships are taken into

account. Yet it is these investigations that contribute

most to our understanding of the deep demersal en-

vironment and the community ecology of fishes there.

Important Species of Demersal Fishes of

Tropical Climates

The Clarias

0010Clarias gariepinus, also known as the African mud

catfish, exists in the wild but it is also cultivated in

ponds, cages, and pens and is of great commercial

importance. This is an omnivorous fish with a prefer-

ence for a planktonic diet. It also feeds on other types

of food items such as insects, insect larvae, pupae,

fish, and fish remains. It also has a propensity for

being carnivorous. Propagation of these fishes is

widely practiced in the tropics. Peak production of

eggs by the female and hatching of the fertilized eggs

are known to take place during the rainy season. A

production mean of about 28 000 eggs and a hatching

rate of 86.4% have been recorded during the rainy

season. A low propagation yield at other times has

been attributed to the resting period in the ovarian

cycle of the animal. Induction of spawning has been

carried out with 11-desoxycorticosterone acetate or

carp pituitary suspension. Some of the processed

products made from Clarias include fermented,

dried, and hot-smoked products. The nutrient con-

tent of Clarias spp. is given in Table 2.

The Ariomma

0011Ariomma bondi and A. melanum are the two species.

The former is found in 200–400 m depth of water; it

is silvery and has a big head with small eyes. A.

melanum inhabits 200–600 m of water, is brown in

color, and has a small head with small eyes. The drift

fish (A. bondi) is a relatively unexploited deep-sea fish

found in tropical West Africa from Senegal to Gabon

and in the western Atlantic from Nova Scotia through

to the Gulf of Mexico. The length range is about

10–19 cm, with a corresponding average weight of

31.88 g. Size is an important technological property

of a fish, of significance to its fishery and subsequent

utilization. The nutrient content of Ariomma spp. is

given in Table 2. The length–weight measurement, as

well as the weight composition, has been found to

tbl0002Table 2 Nutrient content of Ariomma and Clarias spp.

Nutrient Composition

Clarias spp. Ariomma spp.

Moisture 70.5–72.0 75.5–77.5

Protein 18.2–18.6 19.47–20.12

Lipid 6.7–7.1 3.32–3.39

Ash 2.6–2.9 2.67–2.71

2440 FISH/Demersal Species of Tropical Climates

meet the technological requirements of canning. In

canned Ariomma, the edible portion increases from

51.66 to 59.38% when the whole, headless fish with

the soft bones and fins are canned, consequently

increasing the calcium and phosphorus content of

the product. Canned Ariomma will be cheaper than

canned tuna since it is relatively inexpensive and has a

lower processing cost.

Demersal Fisheries

0012 Demersal fisheries use a wide variety of fishing

methods to catch fish on or close to the seabed. It is

defined by the gear used, type of fishing activity, and

varieties of fishes which are caught. A very wide range

of fishing gear is used in demersal fisheries, the main

ones being bottom trawls of different kinds, which

are dragged along the seabed behind a trawler. Other

methods include seine nets, trammel nets, gill nets, set

nets, baited lines and long lines, temporary or per-

manent traps, and barriers. Catches from demersal

fisheries make up a large proportion of the marine

harvest used for human consumption and are the

most valuable component of fisheries on continental

shelves throughout the world.

0013 Demersal fisheries have been a major source of

human nutrition and commerce for thousands of

years. Models of papyrus pair trawlers were found

in Egyptian graves dating back 3000 years. The in-

tensity of fishing activity throughout the world,

including demersal fisheries, has increased rapidly

over the past century, with more fishing vessels,

greater engine power, better fishing gear, and im-

proved navigational aids. Many demersal fisheries

are now overexploited and all are in need of careful

assessment and management if they are to provide a

sustainable harvest.

0014 The products of demersal fisheries are mainly used

for human consumption. The species caught tend to

be relatively large and of high value compared with

typical pelagic species. Demersal fisheries are also

known as ground-fish fisheries.

0015 The five demersal marine fish with the highest

average catches over the decade 1990–2000 are

Alaska pollock, Atlantic cod, sand eels, blue whiting,

and Argentine hake (Table 1). All these species spend

a considerable proportion of their time in midwater.

Sand eels spend most of their lives on or in the seabed.

The vast majority of demersal fisheries take place on

the continental shelves, at depths of less than 200 m.

Management of Demersal Fisheries

0016 It is necessary to manage the demersal fisheries for

biological, social, and economic purposes. Biological

goals used to be set in terms of maximum sustainable

yield of a few main species, but a broader and more

cautious approach is now being introduced, which

includes consideration of the ecosystem within

which these species are produced and which takes

account of the uncertainty in our assessment of the

consequences of our activities. The most important

biological goal is to avoid extinction of species. At a

global level it is evident that economic goals are not

being achieved because the capital and operational

costs of marine fisheries are about two times higher

than the gross revenue.

0017There are large numbers of examples of adverse

social impacts of changes in fisheries, often caused

by the effects of larger, industrial fishing operations

on the quality of life and standard of living of small-

scale fishing communities. Biological management of

demersal fisheries has developed mainly from a

single-species ‘yield-per-recruit’ model of fish stocks.

The yield is controlled by adjusting the mortality and

size of fish that are caught. In many shared inter-

national fisheries, such as those governed by the

European Union, the annual allocation of catch

quotas is the main instrument of fisheries manage-

ment. This requires costly annual assessment of

many fish stocks, which must be added to the operat-

ing costs when looking at the economic balance for a

fishery.

0018The instruments for limiting the size of fish caught

are mesh sizes, minimum landing sizes, and various

kinds of escape panels in the fishing gear. These in-

struments can be quite effective, particularly where

catches are dominated by a single species.

0019There are two classes of economic instruments for

fisheries management: corrective taxes and subsidies

and property rights. The latter demands less detailed

information than the former and may lead to greater

stakeholder participation in the management process,

because it fosters a sense of ownership.

0020The management of demersal fisheries will always

be a complex problem, because the marine ecosystem

is complicated and subject to change as the global

environment changes. Management will always be

based on incomplete information and understanding

and imperfect management tools. A critical step

towards better management would be to monitor

performance in relation to the target objective and

provide feedback in order to improve the system.

0021One of the changes which have taken place over the

past few years is the adoption of the precautionary

approach. This seeks to evaluate the quality of the

evidence, so that a cautious strategy is adopted when

the evidence is weak. Whereas in the past such bal-

ance of evidence arguments were sometimes applied

in order to avoid taking management action unless

FISH/Demersal Species of Tropical Climates 2441

the evidence was strong, the presumption now is that

in case of doubt it is the fish stocks rather than the

short-term interests of the fishing industry which

should be protected. This is a very significant change

in attitude, which gives some grounds for optimism in

the continuing struggle to achieve sustainable fisher-

ies and healthy ecosystems.

Further Reading

Cochrane KL (2000) Reconciling sustainability, economic

efficiency and equity in fisheries: the one that got away?

Fish and Fisheries 1: 3–21.

Cushing DH (1996) Towards a Science of Recruitment in

Fish Populations. Oldendorf/Luhe, Germany: Ecology

Institute.

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

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.

Gulland JA (1988) Fish Population Dynamics: The Implica-

tions for Management, 2nd edn. Chichester: John Wiley.

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

web 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 and Hall.

Kurlansky M (1997) Cod. A Biography of the Fish that

Changed the World. London: Jonathan Cape.

Laevastu T (1996) Exploitable Marine Ecosystem: Their Be-

haviour and Management. Oxford: Fishing News Books.

Pelagic Species 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

Introduction

0001 Of the total world catch of over 80 million tonnes of

fish, roughly 36 million tonnes are accounted for by

groups of typically pelagic fish. Of the total fish catch,

approximately 25 million tonnes are used for reduc-

tion purposes and it is likely that a very high propor-

tion of this comes from pelagic fish landed in bulk.

The production of fish meal from oily fish is around 6

million tonnes, with an associated 1.4 million tonnes

of oil, implying a conversion ratio of about 3.4:1.

Allowing for approximations, these figures imply

that about 70% of tropical pelagic fish caught are

used for purposes other than direct human consump-

tion. In addition to meal and oil, over 1.7 million

tonnes of canned pelagic fish products is produced.

0002The landmass between the tropics of Capricorn

and Cancer (32



S and N) is considered as the

tropical region. Most of this region, barring some

desert areas in Africa and the Indian subcontinent, is

considered to be lush with vegetation and animals

and is characterized by a climate predominantly

determined by annual monsoon rains. From a socio-

economic point of view, the tropics, in spite of its

expected lushness, has some of the poorest and least

developed countries in the world. The great bulk of

mariculture in the tropics takes place on land-based

ponds, which draw sea water through natural inlet

channels, and in shallow bays. Unlike in temperate

regions, offshore culture facilities using large floating

and/or submersible cages are virtually nonexistent. In

particular, the almost exponential growth of the

shrimp culture industry in the last 15 years or so,

and the adverse environmental influences this devel-

opment has had on the coastal environment, and the

future potential in mariculture development in the

tropics as a means of closing the projected gap in

supply and demand for aquatic products, especially

for the upper end of the market, by year 2015, have

created a fresh awareness of tropical mariculture.

Pelagic Environment

0003Microscopic planktonic organisms of the oceans form

the basis of marine food chains and the more complex

food webs. A bucketful of tropical sea water may

contain several thousand microscopic plants and

animals. Microscopic plant life includes all the

members of the phytoplankton that provide food for

herbivores. The phytoplankton is composed of vari-

ous types of unicellular algae, which range from a

few microns to several hundred microns in size. The

major groups of algae include the diatoms, which are

the dominant type of phytoplankton. It is essential for

diatoms to remain in the surface waters to carry out

photosynthetic processes, and therefore these algae

have developed a variety of adaptations to prevent

sinking. Other common types of phytoplankton in-

clude the dinoflagellate algae and coccolithophores.

2442 FISH/Pelagic Species of Tropical Climates

0004 Since all the oceans are connected with one an-

other, and temperature appears to be the most im-

portant factor that limits the distribution of marine

fish, there is basic similarity in the families through-

out the tropical belt (Table 1). Pelagic fish are those

which live at or near the surface of the sea. There are

two categories of pelagic marine fish which form

important fish resources in the tropics: those that

occupy the open ocean, further from the shore and

from the surface (to a mean depth of about 150 m),

are generally large, swift, carnivorous species, such as

tuna, as well as smaller species: the second category

comprises fish which occupy the surface or near-

surface waters of the continental shelf. These fish

are also found in large inland lakes and reservoirs in

the tropics, where species such as clupeids or cypri-

nids are important in commercial and artisan fisher-

ies. These species have been introduced there because

of an increasing demand for fish, and to allow better

utilization of available water resources in such places

(Table 2).

Important Characteristics of Pelagic

Species

0005 There are more kinds of surface-living fish in tropical

and subtropical waters than those of higher latitudes.

The pelagic species are the predominant catches in the

tropics with a total exploitable potential of about 15–

45 10

tonnes. Their common characteristics, in-

cluding abundance and density, allow efficient mass

fishing. Each species has different characteristics,

which sometimes fluctuate with seasons. The con-

tinuity of fisheries for pelagic fish depends not only

on the abundance of the stocks but also on their

distribution. Pelagic fish, being more dependent on

the body of water they are in than on the type of sea

bed, show variable patterns of migration. It is in

warmer seas that the larger members of the mackerel

family (Scombridae) – the tunnies, bonitoes, and

albacores – abound, likewise Coryphaena, the sailors’

‘dolphin’ and shoals of flying fish (Exocoetidae) and

the smaller lantern fish (Myctophidae), upon which

these larger fishes prey. The opah or moonfish (Lam-

pris), the larger sunfish (Mola), and the swordfishes

(Xiphiidae) are also typical of milder conditions. The

northern boundary of these subtropical waters is usu-

ally taken to be a line at the sea surface having a mean

annual temperature of 12



C; this isotherm, as such

lines are called, skirts the south-western tip of Ireland

and the entrance to the English Channel, so that

from time to time in summer some of these exciting

exotics stray into cooler parts. One of the tropical

species which shows a marked variation in chemical

tbl0001 Table 1 Distribution of some pelagic species of commercial importance in the tropics

Species Common

name

West

African

(Atlantic

Ocean)

East

African

(Indian

Ocean)

Central

American

(Atlantic

Ocean)

The Caribbean

(Atlantic

Ocean)

South

American

(Atlantic

Ocean)

South

American

(Pacific

Ocean)

Indian

Ocean

Western

Central

Pacific

Ocean

Eastern

Central

Pacific

Ocean

Engraulis spp. Anchovy þþþþ

Sardina pilchardus Pilchard þþ þ

Sardinops spp. Sardine þþ þþþ

Sardinella spp. Sardinella þþþþþþ

Ethamalosa fimbriata Bonga þþþþ

Scomber spp. Mackerel þþþþþ

Caranx spp. Horse mackerel þþþ þ þ þ þþþ

Reproduced from Johnson AM (1993) Pelagic species of tropical climates. In: Encyclopaedia of Food Science,Technology and Nutrition, vol. 3, pp. 1850–1856.

London: Academic Press, with permission.

tbl0002 Table 2 Some pelagic species in inland lakes and reservoirs

Waterbody Main pelagic species Yield characteristics

Thailand (Ubolratana reservoir) Clupeids 36% of total landing

Mexico Atherinids 40–50 kg ha

1

Surinam (Bokopondo reservoir) Characid Dominant open-water fish

Ghana (Lake Volta) Clupeid 23% of landing

Lake Tanganyika Clupeid 22.5 kg ha

1

Zimbabwe Clupeid 22 kg ha

1

Lake Victoria Clupeid 23 kg ha

1

Nigeria Clupeid 3140 t average biomass

Reproduced from Johnson AM (1993) Pelagic species of tropical climates. In: Encyclopaedia of Food Science,Technology and Nutrition, vol. 3, pp. 1850–1856.

London: Academic Press, with permission.

FISH/Pelagic Species of Tropical Climates 2443

composition is the West African shad (Ethamalosa

dorsalis). This fish shows a range in fat content of

2–7% (wet weight) over the year, with a maximum in

July. It has also been observed that the oil content

of some of these species varies with size. A range of

products can be obtained from the pelagic species of

tropical region. The limitation in utilization is their

small size; nevertheless, these are converted to low-

cost products such as meal and oil.

Examples of Pelagic Species of Tropical

Climates

Sardines

0006 Sardine is a generic term applied to a number of

different kinds of small saltwater fish which are pre-

pared, cooked, and packed in a special way. Sardines

are actually canned herring and the Maine sardine

is the Atlantic herring, Clupea herengus (Figure 1).

The edges of the scales on the belly of these fish are

rough. These species lay their eggs on the seabed;

Atlantic herrings usually lay their eggs at depths of

40–200 m and in some cases intertidally on gravel and

small stones and the Pacific herring spawns on sea-

weed between tidemarks. Both species spawn on

narrow strips. They mature at about 3–4 years of

age and their annual fecundity amounts to 40 000–

100 000 eggs. Throughout life the total fecundity

would be about 10 times greater and only two

survivors are needed to replace the stock. Hence the

annual mortality each year of the eggs, larvae, and

juveniles is high; indeed, it is approximately the in-

verse of the annual fecundity. The natural mortality

of the adults is that sustained under predation in the

absence of fishing and, as might be expected, it is

rather difficult to establish; that of the herring might

be about 10–20% of numbers per year.

0007 These fish travel in huge schools and live in the

open ocean, ranging from Greenland to North

Carolina. The smallest of these herring, 12–17 cm in

length, are dressed and canned as sardines, while

larger ones are cut into small steaks and packed as

‘fish steaks’ or filleted and smoked to make kippered

snacks.

0008Sardinella longiceps is the most important and

widely distributed of all the species in the tropical

environments. Sardines provide a tasty, low-calorie

package. They provide valuable protein, minerals,

vitamins, and cholesterol-reducing omega-3 fatty

acids. Herring has been canned since the early 1780s

when Napoleon recognized that there was a need to

preserve food. Even today with the convenience of the

refrigerator and the freezer, sales of canned food have

been rising yearly. Sardines are also processed with-

out preservatives as they are sterilized by heat in a

sealed aluminum can.

The Maine Sardine

0009The Maine sardine is recognized as the world stand-

ard for excellence in sardines. Around the globe there

are more than 20 varied species packed as sardines,

but it is the tropical sardine that is unsurpassed for

quality. This versatile little fish has long been an

important resource to the state of Maine, longer in

fact than Maine has been a state. Weirs, crude brush-

wood traps, were used to capture the small fish as

they swam in shallow coastal waters. In the nine-

teenth century, Maine commercial fishermen adopted

very similar fishing techniques and set stationary

weirs in coves and along coastal areas that are often

visited by young herring – the fish come in at night

with the flood tide and are left trapped in the weir

when the tide goes out.

0010Today, modern technology has refined the sardine

fishing industry to include the use of large boats

called seiners that take advantage of sophisticated

detection equipment such as depth recorders, echo-

sounding devices, and even light airplanes to watch

for the flash of silver that marks nearby schools of

small herring. The seiners use large nets to encircle

schools efficiently, then a drawstring is pulled to close

the bottom and trap the fish within. The use of

modern-day seines gives fishermen the flexibility to

follow the fish offshore rather than wait for them to

enter stationary shoreside weirs. To insure that only

the freshest product reaches the public, netted fish are

quickly dispatched to modern canneries for careful

processing.

0011The Maine sardine industry had its real beginning

as a result of the Franco-Prussian War of 1870. At

that time, for the US supply of the very popular oil-

fried canned French sardine, it became increasingly

important that the brand should meet high standards

before being released for sale. Every case lost is me-

ticulously inspected and carefully evaluated for strict

adherence to 21 quality factors and it is operated

under the rigorous Hazard Analysis Critical Control

Point program monitored by the Food and Drug

Administration. The nutrient content of tropical

fig0001 Figure 1 The Maine sardine (Clupea herengus herengus).

2444 FISH/Pelagic Species of Tropical Climates

sardines is as follows: moisture 65%; fat 14%; crude

protein 18%; ash 1.7%; inorganic phosphorus

175 mg; and amino nitrogen 105 mg. These charac-

teristics are important to the canning industry.

The Sprats

0012 The sprats, Clupea sprattus (L.), are small clupeoids

about 10–13 cm in length. They live for about 5–7

years, but the most abundant age group is the third

year. Like other clupeoids, they feed on copepods and

other plankton animals. They spawn in spring and

summer, but in the northern Adriatic they spawn

between December and March. They mature from

the end of their second year to the end of their third

year and lay between 10 000 and 40 000 eggs each

year. The natural mortality is probably high. There

are major spawning grounds in the southern North

Sea and in southern Norwegian fjords. The eggs,

larvae, and juveniles are fully pelagic. Sprats are

found in the Baltic, in the North Sea, in the northern

Adriatic and off Romania in the Black Sea. Fisheries

were established in the Scottish firths, between

Bergen and Stavanger in Norway, off Brittanny in

France and around the English coast, particularly in

the Wash and in the Thames estuary. In the main,

these are winter fisheries worked with drift nets and

stow nets, i.e., bag nets hung from fixed poles in the

tidal streams.

The Mackerel

0013 The common mackerel of tropical climates, Scomber

scombrus, is the most important pelagic fish. It occurs

in large shoals and is caught, as the herring is, in drift-

nets when it is in its plankton-feeding phase of spring

and early summer. Mackerels are larger than herring,

reaching as much as 40 cm in length or more. They

spawn in the midwater in productive seas where the

larvae and juveniles grow up, and they spend the rest

of their lives there. They feed on copepods and other

plankton animals. They swim quickly and some of the

larger ones are predatory. The natural mortality of

mackerels is perhaps high, up to 30% of numbers per

year. They do not shoal as herring do but there may be

small and transient aggregations.

0014 The catch of mackerel has been increasing within

the past few years. The catches have reached as much

as one million tonnes from two stocks, one in the

North Sea and the other to the west of the British

Isles. They are found in the Mediterranean but

catches have only amounted to about 30 000 tonnes

each year. Considerable catches of Atlantic mackerel

have been made off the eastern seaboard of the USA.

The stock of Atka mackerel in the North-west Pacific

yielded annually about 100 000 tonnes. The Pacific

mackerel yielded large catches for a period, after

which they declined. The horse mackerel (Trachurus

trachurus L.) has usually been caught in trawls. It is

somewhat larger than the common mackerel.

0015Mackerel meat has higher enzymatic activity than

other fish, and the decomposition of substances re-

lated to adenosine triphosphate (ATP) is quick. The

successful storage of raw mackerel for processing is,

therefore, subject to the temperature used. Frozen stor-

age at 18 to 30



C could give a storage life of about

2–3 months. Storage with crushed ice (0



C) would

keep the fish fresh for about 48 h. Due to the higher

variations in its fat content and its high enzymatic

activity, mackerel present problems during processing

and utilization. The nutrient content of fresh mackerel

shows moisture content of 76%, crude protein 18%,

fat 4%, carbohydrate 0.7%, and mineral 1.3%.

The Menhaden

0016The menhaden (Brevoortia spp.) comprise a group of

species found in the tropical and subtropical west

Atlantic. The most important species is the Gulf

menhaden. B. patronus found in the Gulf of Mexico.

Landings of menhaden showed a slow but steady

increase up to 1993 (1.3 million tonnes) and have

subsequently leveled off at a slightly lower level.

The Capelin

0017The capelin (Mallotus villosus), an arctic fish found

north of the polar front, is caught off the Canadian

seaboard, around Iceland and Greenland and in the

northern parts of the Norwegian and Barents seas.

Landings first became prominent in the mid-1960s

and increased to a peak of 4 million tonnes in 1977.

They have since decreased progressively to only just

over a million tonnes in 1987, partly as a result of the

collapse of the Barents sea stock.

Preservation of Pelagic Fish Quality on

Board and Ashore

0018Overall, the world fisheries biological potential is

about 120 million tonnes and fishery resources

around the world are close to maximum catch limits.

Many of the recent global changes in landings appear

to be more the result of climatic fluctuations of stock

size than of fishery development of management pro-

cesses. There has been a steady increase in landings

during the 1990s; 1997 (110 million tonnes) was

slightly more than the record catch in 1996 (108

million tonnes). Much of the increase is accounted

for by three pelagic shoaling species (Peruvian an-

chovy, South American sardine, and Japanese sar-

dine) and the semi-demersal Alaska pollock. Pelagic

fishing usually gives a single-species catch. When

FISH/Pelagic Species of Tropical Climates 2445

caught in coastal fishing by smaller boats, mixed

catches may demand species sorting as well as size

grading. Traditionally, offshore fishing with big

vessels has been for fishmeal and oil production,

while the coastal fisheries have supplied the fresh-

fish market and the processing industry, especially

canning.

0019 The increasing demand for high-quality raw mater-

ial for all types of production has put pressure on

fishermen to utilize all available knowledge and

organize the processes on board in an attempt to

optimize quality, value, and efficiency to satisfy the

market. Special grades of fishmeal demand the

highest degree of freshness, thereby requiring rapid

and efficient chilling for this type of production. The

interest in using small pelagics as raw material for

animal feed, either as silage or as whole fish frozen in

blocks, is also a challenge for the on-board handling

and storage of fish. Byproducts are of increasing

interest, e.g., roe production and collection of other

raw material for biotechnological utilization. The

choice of using ice or chilled/refrigerated sea water

depends on fish species, the quantity of fish to

be handled, and the type and value of product to be

produced on board or ashore. The use of ice when

boxing pelagic fish for human consumption was long

regarded as uneconomical, but the development of

methods for automatic addition of ice has made this

more attractive. Likewise, improved methods of in-

ternal transport and storage using new methods for

identifying and labeling each box, which can be

monitored and recorded by microprocessor tech-

niques, are important developments.

0020 Filleting of fish on board is a specialized process

and increases the product value, but sets certain limits

on fishing capacity and often on processing flexibility.

The advantage of on-board processing is that fresh-

ness can be assured. Also, the question of full utiliza-

tion of the catch is important; today dumping is too

easy and fish are wasted in an effort to store only the

most valuable products.

0021 Highly specialized vessels for surimi production

based on pelagic fish have been developed but, so

far, this venture has not been successful due to many

technical problems and limited availability of suitable

fish resources.

Chilling

0022 Many of the pelagic resources are found close to

the shores, giving small vessels the opportunity to

participate in the fisheries. The need for chilling is

important, particularly when temperatures are high

(> 15



C), while low temperatures may allow bulk

transport if the distance is short. Sorting of fish is

necessary ashore due to both damage and autolysis,

which increases at high temperatures. Often only a

small part can be utilized for consumption. Small

vessels can improve handling and increase quality of

the catch by using boxes or small insulated containers

with ice or CSW. It is important to avoid anaerobic

conditions in containers without circulation. There-

fore the system of pumping air via perforated pipes

into the bottom of the containers can be used. Many

such installations have been tried out and proven to

be beneficial. To reach a practical solution to benefit

the fishermen, quality must be paid for; otherwise

new investments will not be made. The Food and

Agriculture Organization has been heavily involved

in giving advice and is undertaking projects to in-

crease the utilization of small pelagics for human

consumption. In some cases when small pelagics are

intended for curing or salting and sun drying, the

process may start on board. Containers with brine,

or chilled brine, can be used, starting the brining on

board so that high-quality raw material can be

brought back for sun drying. The best results are

achieved when small fish are chilled and brined rap-

idly. Bigger fish (> 25 cm) should be gutted if the brine

is not chilled.

Canning

0023In many countries canning is the most important

utilization of small pelagics. The many different prod-

ucts of sprat, sardine, herring, mackerel, pilchard,

and tuna are well accepted. This is important in the

market due to good storage stability and high nutri-

tional value. Fish for canning must be of the highest

quality, and because most small pelagic fish are very

delicate, damage due to handling often results in a

high degree of postharvest losses. Also, the many old

purse seiners operating without chilling make sub-

stantial losses, especially in areas with high tempera-

tures such as India, California, Chile, or Peru and

South Africa. Autolysis in combination with rough

handling results in belly bursting, which is very de-

pendent on storage time and temperature. Reducing

storage time and temperature can greatly improve the

quality of the raw material. Chilling is of the utmost

importance and only a few hours’ delay at 15–20



will reduce storage ability by several days. This means

that the quality of landings of small pelagic fish for

canning is dependent on season and fish species, on

the chilling rate on board, and on the loading or

unloading method. The bigger fish can often with-

stand rough handling. Disintegration of fish results in

lower productivity in the processing plant. In a Mex-

ican canning plant the quantity of sardines nabbed by

machine decreased from 160 to 60 kg per person per

hour when the proportion of belly burst increased

from zero towards 100%. For the small fatty species,

2446 FISH/Pelagic Species of Tropical Climates

oxidation must also be avoided. For fresh consump-

tion and canning it is not a problem if chilling is done

properly and if fish is utilized within 2–4 days, as is

usually the case.

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

as Food; Pelagic Species of Temperate Climates; Hazard

Analysis Critical Control Point