1 Introduction and History of Cage Culture
Chua Thia Eng
1
and Elsie Tech
2
1
Partnerships in Environmental Management for the Seas of East Asia (PEMSEA),
DENR Compound, Visayas Avenue, Quezon City, Philippines;
2
Asian Fisheries Society
25-A Mayaman Street, UP Village, Quezon City, Philippines
History of Cage Culture
Open sea activities, such as cage and pen
culture, are viewed by many stakeholders in
the industry as the aquaculture system of
the millennium. Fish production from cages
and pens (both in freshwater and marine
environments) contributes significantly to
total foodfish produced. Cage culture has
made possible the large-scale production of
commercial finfish and will probably be
the most efficient and economical way of
raising fish.
Aquaculturists realize the need to limit
further conversion of wetlands and man
-
groves into traditional aquaculture farms.
We face a situation where even freshwater
ecosystems have reached critical levels
with respect to their carrying capacities.
The depletion of ocean and coastal fishery

early as 1960. The cage culture of common
carp (Cyprinus carpio) in lakes also started
at this time (Kuronuma, 1968). Since the
1970s, Thailand has developed cage culture
techniques for two important marine finfish:
the seabream (Pagrus major) and grouper
(Epinephelus spp.) (Coche, 1976). Chua and
Teng (1978) pioneered the development of
cage culture methods/designs for groupers
in Malaysia, although large-scale cage farm
-
ing in marine waters really gained ground in
the 1980s and in inland waters in the 1990s
(Shariff and Nagaraj, 2000). Korea started
growing a European variety of common carp
and maintained yellowtail in holding cage
enclosures in the late 1970s. By the end
of 1980, cage culture of the olive flounder
(Paralichthys olivacens) and black rockfish
©CAB International 2002. Diseases and Disorders of Finfish in Cage Culture
(eds P.T.K. Woo, D.W. Bruno and L.H.S. Lim) 1
(Sebastes schlegeli) was established, and
developed into a successful aquaculture
industry in the 1990s (Kim, 2000). Cage
culture of groupers (Epinephelus spp.) in the
Philippines has been practised since the
1980s. Mariculture of milkfish in the 1990s
led to the further growth and development of
the industry (Marte et al., 2000).
In Europe, cage culture of rainbow trout

Freshwater aquaculture was limited to
availability of water while mariculture had
to rely on only 3000 km of coastlines (the
majority of which did not have sheltered
bays or lagoons). In the years that followed,
efforts were geared towards improvement in
the culture of tilapia and cage design (Coche,
1976).
Currently many fish species have been
cultivated in various designs and sizes of
cages in Asia, Europe and other parts of
the world (Table 1.1). Tilapia and carp pre-
dominate in freshwater cage culture in Asia,
while salmonids are commonly farmed in
Europe and the Americas.
2 T.E. Chua and E. Tech
Species cultured Country Reference
Anguillidae
Anguilla japonica
(eel)
Bagridae
Mystus nemerus
(mystid catfish)
Chanidae
Chanos chanos
(milkfish)
Channidae
Channa macrocephalus
Channa micropeltes
(snakehead)

Lin (1990)
Thana (1995)
Pantulu (1976); Thuoc (1995)
Pantulu (1976); Thuoc (1995)
Ang
et al
. (1988)
Chellappa
et al
. (1995)
Ang
et al
. (1988)
Norberg and Stenstroem (1993)
Norberg and Stenstroem (1993)
Mazid (1995)
Shariff and Nagaraj (2000)
Table 1.1a.
Major species of freshwater finfishes cultured in cages.
Introduction and History of Cage Culture 3
Species cultured Country Reference
Red tilapia
Sarotherodon aureus
Sarotherodon esculentus
Sarotherodon galilaeus
Sarotherodon mossambicus
Sarotherodon mossambicus
×
S. honorum
(hybrid)

Tanzania
Nigeria
Philippines
Taiwan
Guatemala
USA
Sri Lanka
Ivory Coast
Nigeria
Kenya
Philippines
Brazil
Dominican
Republic
Togo
USA
Sierra Leone
Togo
Dominican
Republic
Nigeria
Colombia
Zimbabwe
Tanzania
Togo
Kenya
Nigeria
Vietnam
South Africa
Egypt

et al
. (1972)
Suffern
et al
. (1978)
Anon. (1980); Muthukumarana and Wcerakoon
(1987)
Coche (1975, 1976, 1977, 1978); Campbell (1976);
Shehadeh (1976); de Kimpe (1978); Amoikon
(1987)
Konikoff (1975); Campbell (1987)
Haller (1974)
PCARRD (1981); Aragon
et al
. (1985); Guerrero
(1985, 1996)
FAO (1977)
Olivo (1987)
Issifou and Amegavie (1987)
McGinty (1991)
Iscandari (1987)
Issifou and Amegavie (1987)
Olivo (1987)
Ali (1987)
Patino (1976); McLarney (1978); Popma (1978)
Norberg and Stenstroem (1993)
Ibrahim
et al
. (1974)
Issifou and Amegavie (1987)

(slender
carp/sultan fish)
Nile carp
River carp
Eleotridae
Goby
Oxyeleotris marmoratus
(sand
goby)
Ictaluridae
Ictalurus punctatus
(Channel
catfish)
Moronidae
Morone chryops
×
M. saxatilis
(sunshine bass)
Osphronemidae
Osphronemus gourami
(giant gouramy)
Malaysia
Philippines
Sri Lanka
India
Indonesia
Iran
Cambodia
Cambodia
Malaysia

Malaysia
Ang
et al
. (1988)
Fermin (1990); Marte
et al
. (2000)
Muthukumarana and Weerakoon (1987)
Basavaraja (1994)
Costa-Pierce and Effendi (1988)
Matinfar and Nikouyan (1995)
Thana (1995)
Thana (1995)
Ang
et al
. (1988)
Pradhan and Pantha (1995)
Muthukumarana and Weerakoon (1987)
Lovatelli (1997)
Siemelink
et al
. (1982); Ishak (1987)
Huisman (1979)
Bandyopadhyay
et al
. (1991)
Lopez (1995)
Filipiak (1991); Mamcarz (1992)
Evtushenko (1994)
Pradhan and Pantha (1995)

Schmittou (1969); Perry and Avault (1972); Collins
and Delmendo (1979); Parker (1988); Masser and
Duarte (1992); Burtle and Newton (1993); Webster
et al
. (1994)
Kelly and Kohler, 1996; Pagan (1970); Suwanasart
(1971); Pagan-Font (1975)
Ang
et al
. (1988)
Ang
et al
. (1988)
Table 1.1a.
Continued
.
Introduction and History of Cage Culture 5
Species cultured Country Reference
Pangasiidae
Pangasius bocourti
(yellow catfish)
Pangasius conchophilis
Pangasius hypophthalmus
(catfish)
Pangasius lardnaudi
Pangasius micronemus
Pangasius nasutus
(catfish)
Pangasius pangasius
(river

Siluridae
Silurus glanis
(sheat fish)
Esox lucius
(pike)
Puntius gonionotus
(minnows)
Puntius schwanenfeldii
(tinfoil barb)
(minnows)
Puntius
spp.
Vietnam
Vietnam
Cambodia
Vietnam
Cambodia
Cambodia
Vietnam
Vietnam
Thailand
Malaysia
Malaysia
France
Germany
Poland
Finland
Germany
Russia
France

Thuoc (1995)
Menasveta (2000)
Shariff and Nagaraj (2000)
Ang
et al
. (1988)
Tamazouzt
et al
. (1993)
Marciak (1979)
Mamcarz (1984)
Mamcarz (1984)
Schultz
et al
. (1993)
Jager and Nellen (1981)
Champigneulle and Rojas-Beltran (1990)
Mamcarz and Kozlowski (1992)
Menton (1991)
Srivastava
et al
. (1991); Cornel and Whoriskey
(1993)
Torrissen
et al
. (1995)
Matinfar and Nikouyan (1995)
Alanaerae (1992)
Mamcarz and Szczerbowski (1984)
Torrissen

male (Florida red tilapia)
Moronidae
Morone chryops
×
M. saxatilis
(sunshine
bass)
Pisodonophis
Pisodonophis boro
(brackishwater eel)
Salmonidae
Coregonus lavaretus
(Baltic whitefish)
Oncorhynchus mason rhodurus
(Amago
salmon)
Salmo salar
(Atlantic salmon)
Philippines
USA
USA
Vietnam
Germany
Yugoslavia
USA
Guerrero (1996); Ramos (1996); Bagarinao
(1998); Marte
et al
. (2000)
Rust

Centropomus nigrescens
(snook)
Lates calcarifer
(seabass)
Japan
Taiwan
Ecuador
Hong Kong
Japan
China
Korea
Iran
Russia
USA
Ecuador
France
Ecuador
China
Hong Kong
Indonesia
Malaysia
Philippines
Singapore
Thailand
Vietnam
Australia
Watanabe (1988a,b)
Su
et al
. (2000)

et al
. (1995)
Toledo
et al
. (1991); Fermin
et al
. (1993);
Alcantara
et al
. (1995); Lopez (1995)
Anon. (1986); Cheong and Lee (1987)
Sakaras (1984); Kungvankij (1987a); Tookwinas
(1990b); Chaitanawisuti and Piyatiratitivorakul
(1994a)
Lovatelli (1997)
Barlow
et al
. (1995); Rimmer (1998)
Table 1.1c. Major species of marine finfishes cultured in cages.
Introduction and History of Cage Culture 7
Species cultured Country Reference
Characidae
Piaractus mesopotamicus
(pacu)
Cichlidae
Oreochromis spilirus
(tilapia)
Oreochromis urolepsis hornorum
×
O.

Oplegnathus fasciatus
(rock bream)
Paralichthyidae
Paralichthys olivaceus
(bastard
halibut/flounder)
(olive flounder)
Percichthyidae
Lateolabrax japonicus
(Japanese
seabass)
Percidae
Stizostedion lucioperca
(wild zander)
Pleuronectidae
Hippoglossus hippoglossus
(Atlantic
halibut)
Brazil
Kuwait
USA
Vietnam
Nepal
Norway
Canada
China
Malaysia
Philippines
Singapore
Thailand

. (1991)
Lovatelli (1997)
Pradhan and Pantha (1995)
Kaspruk and Tvejte (1994); Hjelt (2000)
Jones and Iwama (1990)
Yongjia
et al
. (1996)
Ali (1987); Hannafi
et al
. (1995)
Emata (1996)
Cheong (1988)
Doi and Singhagraiwan (1993); Chaitanawisuti
and Piyatiratitivorakul (1994b)
Su
et al
. (2000)
Hannafi
et al
. (1995)
Lee (1982); Anon. (1986)
Yongjia
et al
. (1996)
Wong (1995)
Rahim (1982)
Tanomkiat (1982)
Su
et al

. (1994)
Continued
8 T.E. Chua and E. Tech
Species cultured Country Reference
Limanda herzentein
(brown sole)
Limanda punctatissima
(longsnout
flounder)
Rachycentridae
Rachycentron canadum
Salmonidae
Caspian salmon
Onchorynchus kisutch
(Coho salmon)
Oncorhynchus mason rhodurus
(Amago
salmon)
Oncorhynchus mykiss
(rainbow trout)
Oncorhynchus tshavytocha
(Chinook
salmon)
Prosopium
Salmo salar
(Atlantic salmon)
Salmo trutta
(broom trout)
Salvelinus alpinus
(Arctic charr)

Japan
Taiwan
Iran
Chile
Yugoslavia
Canada
Canada
Germany
Canada
Scotland
Norway
USA
France
Norway
Ecuador
Thailand
France
China
Korea
France
Vietnam
Philippines
Hong Kong
Japan
Vietnam
China
China
Taiwan
Hong Kong
Philippines

Kraakenes
et al
. (1991)
Rottiers (1994)
Arzel
et al
. (1993)
Torrissen
et al
. (1995)
Benetti
et al
. (1995)
Menasveta (2000)
Trebaol (1991)
Liu
et al
. (1991)
Kim (1995)
Vigneulle and Laurencin (1995)
Tuan and Hambrey (2000)
Sayong (1981)
Chao and Lim (1991); Wong (1995)
Ukawa
et al
. (1966); Chao and Lim (1991)
Tuan and Hambrey (2000)
Chao and Lim (1991); Wong (1995)
Chao and Lim (1991)
Maruyama and Ishida (1976)

Epinephelus sexfaciatus
Epinephelus
spp.
Epinephelus suillus
Epinephelus summana
Epinephelus tauvina
(green grouper,
estuarine grouper)
Siganidae
Siganus canaliculatus
(rabbit fish)
Siganus guttatus
(siganid)
Sillaginidae
Sillago sihama
(sand whiting)
Sparidae
Acanthopagrus schlegeli
(black
seabream)
Chrysophrys major
(red pargo)
Mylio latus
(yellow finned seabream)
Puntazzo puntazzo
(sheepshead bream)
Rhabdosargus sarba
(goldlined
seabream)
Sparrus aurata

India
Indonesia
Malaysia
Philippines
Singapore
Singapore
Kuwait
Indonesia
Philippines
Vietnam
India
Korea
China
Hong Kong
Hong Kong
Israel
Hong Kong
Israel
Israel
China
Japan
Korea
Chao and Lim (1991)
PCARRD (1986); Quinitio and Toledo (1991)
Hamsa and Kasim (1992)
PCARRD (1986); Quinitio and Toledo (1991)
Yongjia
et al
. (1996)
Kohno

Lanjumin (1982)
Chua and Teng (1978); Rahim (1982); Ali (1987)
Kohno
et al
. (1988); Lopez (1995)
Cheong and Lee (1987)
Chao and Lim (1991)
Hussain
et al
. (1975); Chao and Lim (1991)
Tacon
et al
. (1990)
Lopez (1995); Soriano
et al
. (1995)
Lovatelli (1997)
James
et al
. (1985)
Kim (1995)
Yongjia
et al
. (1996)
Wong (1995)
Wong (1995)
Kissil (1996)
Wong (1995)
Kissil (1996)
Porter

activities started to move toward offshore
areas. The lack or non-availability of
sheltered sites in many regions because of
varied coastline configurations, the build-up
of organic matter in closed bays due to poor
water exchange, and use conflicts between
industries and tourism for sea water were the
main reasons for such a shift (Lisac, 1991).
Some of the offshore cage systems
that later developed include: Dunlop
Tempest I (Fearn, 1991); ‘SADCO’ cages
(Muravjev et al., 1993); Ocean Spar
(Loverich and Croker, 1993); Farmocean
system (Gunnarson, 1993); Seacon system
(Lien, 2000); and Bridgeton Hi-Seas
(Gunnarson, 1993; Lien, 2000).
Muir (1998) considered the following
criteria important for success in offshore
cage culture: (i) location (> 2 km from
shore); (ii) environment (average waves
> 5 m, regularly 2–3 m oceanic swells,
variable wind periods); (iii) access (about
80% of the time when cages are accessible to
working staff); and (iv) operation (remote;
with automated feeding devices and long-
distance monitoring).
Advantages and Limitations of
Cage Culture
In general, cage culture practices have
numerous advantages over other culture

of large sheltered coastal waters in many
countries, marine cage farming can play
a significant role in increasing fish
production.
Cage culture systems vary in terms of
farm size and intensity of operation. Floating
cages, for instance, in Korea can reach yields
exceeding 500 t ha
−1
(ADB/NACA, 1998).
Cage Design
Cage design is determined by conditions in
the culture site, as well as the ecological
requirements and behaviour of the target
species for culture. Each design is site-
specific and knowledge of the topography,
wind force, wind direction, prevalence of
storms, monsoons, wave load, current
velocity and water depths are important
parameters for consideration. In designing
cages, it is also important to consider the
rate of biofouling and the species composi
-
tion of the marine fauna in and around the
potential site (Chua, 1982). A checklist of
10 T.E. Chua and E. Tech
fish species popularly cultured in Asia with
cage and culture specifications is provided
in Table 1.3.
Types of cages

cages are used in lakes, protected bays and
lagoons, sheltered coves and inland seas.
The surface-floating unit consists of floats,
framework and netcage. Most floating cages
Introduction and History of Cage Culture 11
Advantages Limitations
Maximizes use of available water resources
Reduces pressure on land resources
Combines several types of culture within one water
body; treatments and harvests independent
Ease of movement and relocation of cages
Intensification of fish production (high densities and
optimum feeding result in improved growth rates,
reducing rearing period)
Optimum utilization of artificial food improves food
conversion efficiencies
Easy control of competitors and predators
Ease of daily observation of stocks for better
management and early detection and treatment of
parasites and diseases
Reduces fish handling and mortalities
Easy fish harvest
Storage and transport of live fish facilitated
Initial investment is relatively small
Locations restricted to sheltered areas
Requires back-up food store, hatchery and
processing facilities
Needs adequate water exchange to remove
metabolites and maintain high dissolved oxygen
levels; rapid fouling of cage walls requires frequent

calcarifer
)
Rectangular marine pen, 20 × 50 × 60 m
(1000 m
2
× 6 m); wood, bamboo, polythene
net
Cylindrical floating netcage, 2 m diameter
× 2 m depth (6 m
3
); wood, bamboo,
polythene and 200 l plastic drums for floats
Box-shaped floating netcage, 5 × 5 × 3m;
wood and plastic drums
Rectangular broodstock floating netcage
4 × 4 × 3 m, installed with a hapa net of the
same dimension with mesh size of
0.4–0.6 mm as egg collector; made of
bamboo, wood and 200 l plastic drums
Circular or rectangular broodstock floating
netcages, 4 × 4 × 3mor10× 10 × 2 m nylon
mesh of size 4–8 cm
2 × 2 × 1.5mor10× 5 × 1.5 m floating
netcage
3 × 3 × 2 m floating netcage
2.5 × 2.5 × 1.5 m bamboo and polythene
netting
5 × 5 × 2 m, galvanized iron pipe and
bamboo, concrete weight
Stocking density is 30,000 fingerlings weighing 10 g; feeding

period; production of 350–600 g to 2–3 kg per fish
Stocking density is 15–25 fish m
−3
of size 2–3 inches; feeding
with trash fish once daily; 6–8 months of culture; production of
500–600 g per fish
Stocked with juveniles; feeding with trash fish at 5% of body
weight twice daily, with FCR of 3.6:1; 4 months culture period;
growth rate of 4 g per day
Stocking density of 12–300 fish m
−3
; feeding fresh trash fish
twice daily, with FCR of 4–10:1; 12 months culture period;
production of 1 kg per fish, 80–95% survival
Philippines (Ramos,
1996; Bagarinao, 1998)
Thailand (Chaitanawisuti
and Piyatiratitivorakul,
1994a)
Singapore (Anon.,
1986)
Philippines (Toledo
et al
.,
1991)
Australia (Rimmer,
1998)
Australia (Barlow
et al
.,

(grow-out)
Stocking density is 20–30 fish m
−3
measuring 9–10 cm, feeding
with commercial feeds; 7–8 or 12–14 months of culture;
production of 600–800 g per fish or 1.2–1.4 g per fish
Stocking density is 44 fish m
−3
of size 80–100 g; feeding with
trash fish at 3–5% of body weight twice daily; 6–7 months of
culture; production of 600 g per fish, 90% survival
Stocking density is 120 fish m
−3
of size 13–15 cm (grow-out),
5–13 cm (transition), or 2–3 cm (nursery); feeding with dry
pellets and minced trash fish (grow-out) or
Chlorella,
Brachionus
and
Artemia
(nursery); FCR of 2.5–2.8:1 for dry
pellets and 6.3:1 for trash fish; culture period of 1 month
(nursery), 3 months (transition) or 8 months (grow-out);
production of 500–800 g per fish
Stocking density is 10–100 m
−3
of size 7.5–10 cm; feeding with
artificial feeds and live or frozen trash fish and crustaceans,
feeds given at 10% body weight during the first 2 months, 5%
thereafter until harvest; 8 months culture period; production of

1990a)
Thailand (Chaitanawisuti
and Piyatiratitivorakul,
1994b)
Thailand (Doi and
Singhagraiwan, 1993)
Continued
14 T.E. Chua and E. Tech
Species
Cage/pen
dimension
Culture specifics
Country/
references
Golden snapper
(
Lutjanus jobni
)
Red seabream
(
Pagrus major
)
Yellowtail (
Seriola
quinqueradiata
)
Rabbitfish (
Siganus
canalculatus
)

Stocking density is 44 fish m
−3
of size 80–100 g; feeding with
trash fish at 3–5% of body weight once or twice daily; 6–7
months of culture; production of 600 g per fish
Stocking density is 100 fish m
−3
(1-year-old fish); feeding with
trash fish (anchovy and sardines) and moist pellets; 1–7 years
culture period; production of 800 g to 1.4 kg per fish
Stocking density is 115–340 fish m
−3
of size 200–500 g or 5 fish
m
−3
for size 1 kg; feeding with trash fish (anchovy, sardines,
sand lance) and moist pellets; feed given 1–4× daily at 1–3% of
body weight or at 4–8% of body weight for fish less than 100 g;
FCR of about 5–9:1; 1–2 years culture period; production of
2.5–6 kg per fish
Stocking density is 25 fish of size 0.89 g per cage; feeding with
moist pellets once every 2 days at 3% of body weight; 20
months culture period or until fish reach maturity and spawning
(about 3.7 kg size)
Stocking density is 15 fish of size 48–68 g per cage; feeding
with formulated diet, given 2× daily to satiation; 100 days culture
period; production of 119 g per fish, 100% survival
Stocking density is 1 kg m
−3
(8–10 fish per kg); no feeding; 6

Malaysia (Ang
et al
.,
1988)
FCR, food conversion ratio.
Table 1.3.
Continued
.
have a rigid wooden or metal framework
surrounded by a catwalk to facilitate
operation and maintenance. The net bag is
supported by a buoyant collar or a frame,
and can be designed in various shapes and
sizes.
Floats. Common flotation materials in
-
clude metal, plastic drums, PVC pipes, Sty
-
rofoam, cement blocks, rubber tyres with
polystyrene, bamboo and logs. Metal drums
coated with tar or fibreglass are popular
because they are cheap, but they corrode
easily in seawater and have a life span
ranging from 0.5 to 3 years (IDRC, 1979).
Fibreglass drums or buoys are preferred by
commercial fish farmers as they can last for
many years in seawater although the initial
cost is comparatively higher. Styrofoam
blocks, covered with polythene sheets
provide good buoyancy and may last for as

vinyl-coated mesh) mounted on rigid metal
or wooden frameworks, are also commonly
used in sea farming (Swingle, 1971; Powell,
1976; Milne, 1979). The relative merits of
flexible and rigid cages are discussed by
Hugenin and Ansuini (1978). The choice
of flexible or rigid types is dependent on
economics. Flexible cages are more widely
used in developing countries because of
lower cost.
Mesh size. This is determined by the size of
the fish to be stocked. Small mesh size nets
become clogged, especially in tropical areas,
and easily damaged by floating objects and
increased drag force and hence affect the
morning load of the cages. As the fish grow,
a larger mesh size should be used (Chua,
1979).
Introduction and History of Cage Culture 15
Fig. 1.1. Set net showing typical netcage structure (King Chou Fish Net Manufacturing Co., Ltd).
Rotating and non-rotating floating cages
Rotating cages have been designed
primarily to reduce the impact of fouling
organisms and insects. The cage rotates
from a central axis attached to a solid
floating framework (Christensen, 1995).
Non-rotating types are widely used and may
be designed with narrow or wide collars.
Rigid narrow collars made of non-wooden
materials (glass fibre and steel) and buoys

1972). Other forms of cages such as orthogo-
nal (Anon., 1976; Milne, 1979) and octagonal
(Møller, 1979) have been used for salmonid
culture in Scotland, Norway and France.
The size of cages ranges from less than
1 m
3
to 50,000 m
3
. Freshwater cages for
tilapia in the Philippines and Indonesia are
16 T.E. Chua and E. Tech
Fig. 1.2. Submersible cage for yellowtail (from Fujiya, 1979).
usually very large (exceeding 100 m
3
) and
are installed in calm shallow lakes (Chua,
1982). Currently, dimensions for marine
cages are usually smaller, even in relatively
calm waters, because large nets are difficult
to maintain due to biofouling problems in
the marine environment. Although large
size cages reduce construction costs, the
optimum size must be within the physical
capacity of the fish farmer(s) to manage and
maintain. For tropical conditions where
biofouling can be rapid and heavy, net cage
sizes are between 20 and 50 m
3
. Various

18 T.E. Chua and E. Tech
Fig. 1.5. Square cage (Fong Yu).
Fig. 1.6. Square cage (Water Diamond Equipment Co., Ltd).
Fig. 1.7. Cage structures by EKSPORTFINANS
ASA.
cage culture. High stocking density may
create group effects resulting in high mor
-
tality, as in estuary grouper (Epinephelus
salmoides) (Chua and Teng, 1978). Optimal
stocking density ensures optimum yield
for food conversion, and low disease
prevalence with good survival rate.
Feeding
Feeding is a vital operational function
and is affected by the interplay of many
biological, climatic, environmental (water
quality) and economic factors. Growth rate
is affected by feeding intensity and feeding
time (Chua, 1982). Each fish species
varies in maximum food intake, feeding
frequency, digestibility and conversion
efficiency. These in turn affect the net yield,
survival rates, size of fish and overall
production of the cage. Trash fish is the
main feed for yellowtail, grouper, bream,
snapper and other carnivorous species
cultured in marine cages (Anon., 1986;
Quinitio and Toledo, 1991; Doi and
Singhagraiwan, 1993; Leong, 1998). The

Maintenance work is also of vital impor
-
tance. The entire structure (raft and netcages)
must be routinely inspected. Necessary
repairs and adjustments to anchor ropes and
netcages should be carried out immediately.
Plastic drum floats have to be regularly
painted with non-toxic antifouling paints.
Scraping accumulated fouling organisms
may be carried out by rotating the drums
regularly. Monthly replacement of net
20 T.E. Chua and E. Tech
Fig. 1.10. Ocean catamaran fish farm.
Fig. 1.11. Aqualine prefabricated mooring system.
structures should also be considered, as this
ensures a good water exchange in the net,
thereby washing away faeces and uneaten
food.
Biofouling
Biofouling is an important and common
problem in cage culture. The rate of
biofouling in tropical waters is faster than
in subtropical and temperate regions. The
net walls, as well as the firm structures such
as the floats, can be covered with biofouling
organisms. Common fouling organisms
include barnacles (Balanus spp.), green
mussels (Perna spp.), oysters (Crassostrea
spp.), algae and tunicates. Biofouling clogs
the mesh of the net, reducing the rate of

(Scatophagus argus) can be used to control
biofoulers (Beveridge, 1987), but their
application on a large scale needs to be
assessed.
Routine checking of moorings will
normally require a diver. In addition, regular
lifting of the nets to check for predators and
damage caused by poachers has to be carried
out. Air- or sun-drying of nets at regular
intervals will allow removal of debris and
other materials that clog the mesh and block
water exchange. Checking and cleaning of
walkways should be routine procedures to
avoid accumulation of slime, which makes
walkways slippery. Boats used for monitor
-
ing should also be regularly serviced and
equipped with back-up motor engines and
emergency flares.
Regulation of fish growth and production
An important farm management strategy
is the skilful manipulation of operational
functions such as stocking density and
feeding. The main purpose is to regulate
fish growth to attain the desired size for the
targeted market and season. For the estuary
grouper (Epinephelus tauvina), at water
temperatures between 29 and 30°C and
feeding to satiation daily, a fingerling of
15–16 g will attain marketable size of 500 g

to outbreaks of infectious diseases and an
increase in prevalence of parasites. Infec-
tious diseases in fish culture are not only
accentuated by waste pollution, but exacer-
bated by crowding, handling, temperature
and biofouling. The most common fish dis-
ease in cages is vibriosis caused by Vibrio
spp. Furthermore, abrasions cause fin and
skin damage to cultured stocks (Moring,
1982). Occurrence of infection/disease may
be minimized by selecting good sites,
proper mooring and observance of optimal
stocking densities and careful handling of
stocks (Boydstun and Hopelain, 1977).
Adequate spacing between cages and farms
is also an essential management tool to
reduce the spread of disease (Wong, 1995).
Monitoring of water quality
Constant monitoring of water quality is
an essential routine. The farmer should
be sensitive to and aware of threats such as
pollutants caused by industrial discharge or
indicators of the occurrence of algae blooms
such as red tides. The routine monitoring of
water quality is a useful practice.
Predation
Information on the actual extent of
problems related to predation is scanty
(Beveridge, 1987). Mills’ (1979) survey in
Scotland recorded a nearly 90% predation

countries.
Government role
Cage farms should be licensed and farm
sizes limited. For example, a cage farm in
Korea is limited to 0.5 and 1 ha for each
culture bed, with 300 m waterway between
cages with the cage area exceeding 20% of
the licensed area (Kim, 1995). In May 1997,
the central government in Korea ruled that
all inland water cage farms be dismantled
upon expiration of the 10 year licence
agreement (Kim, 2000). Size restrictions
have also been implemented in most parts
of Scandinavia (Beveridge, 1987). In Fin
-
land, small units with annual production of
less than 3 t need to notify the authorities,
while those producing over 40 t require
Introduction and History of Cage Culture 23
government permits (Beveridge, 1987).
Before 1983, Norwegian salmon farms
observed size restrictions (at a volume of
8000 m
3
), and by 1985, 150 new licenses
were issued. Certain countries have
allocated specific areas for cage culture
development. In Hong Kong and Singapore,
for instance, legislations apply to marine
cage farms, while in the Philippines, laws

tigation together with other considerations
indicated in Table 1.4. This information is
needed to plan the scale of the venture,
design and size of cages, assessment of carry
-
ing capacity for stocking rate, feeding strat
-
egy and other operational and management
purposes (Chua, 1982).
Lakes, bays, lagoons, straits and inland
seas are ideal sites for cage culture provided
these sites are protected from strong winds
and rough weather and have sufficient water
movements. Vertical stratification in deep
water areas may pose problems with respect
to wide fluctuations in oxygen and pH
levels. Before the start of the venture it is
also important to have baseline data on the
seasonal variation of salinity, temperature,
water current, turbidity, dissolved oxygen
and primary productivity. Whenever possi-
ble, suitable areas should also be free from
potential predators.
Selection of species for culture
Knowledge of the biology of each fish
species is crucial in optimizing production
from cages. The selection of fish should be
based on a number of biological criteria
(omnivore or carnivore, hardiness, fast-
growing, efficient food conversion ability,

Cage culture systems contribute wastes
(solid and soluble) to the aquatic environ
-
ment from uneaten food, dust, fish faeces,
scales, mucus and other debris. These may
accumulate beneath the cages or down
-
stream, and result in a reduction in
dissolved oxygen, and a build-up of wastes
in the water (Beveridge et al., 1982; Penczak
et al., 1982; Beveridge, 1984; Phillips et al.,
1985; Phillips and Beveridge, 1986; Heping,
1995; Yusuf et al., 1995). The accumulation
of uneaten food and waste leads to the
formation of hydrogen sulphide, and high
levels may cause fish mortality. Improper
use of antibiotics and their release into the
aquatic environment may result in the dev-
elopment of antibiotic-resistant bacteria.
Cage culture can introduce and/or
disrupt disease and parasite transmission,
cause changes to the aquatic flora and
fauna, and may even alter the behaviour
and distribution of local fish communities
(Loyacano and Smith, 1976; McGuigan and
Sommerville, 1985; Phillips et al., 1985).
The escape of non-indigenous species from
culture cages may alter the species com
-
position of indigenous fish, especially in

fry gathering, net making and mending, cage
construction and feed preparation.
Problems and Major Constraints
Usual problems reported include mooring
systems, which may cause additional high
loads on the cage structure, pollution from
excess feed, and limited waste dispersion
due to insufficient or slow water movement
around cages. Furthermore, poaching and
vandalism, severe damage caused by
typhoons and long winter monsoon peri
-
ods, and disease outbreaks are constraints
for aquaculture.
Other constraints include the supply of
ova, expensive feed, lack of adequate feed,
congestion on existing farm sites and lack of
new sites for expansion (limited resource
base).
Conclusion
Fish culture using cages has proven to
be technically and commercially viable in
most countries. Future development in the
industry should be geared towards the use
of cheaper and more ‘environment friendly’
floating facilities, higher quality netting
Introduction and History of Cage Culture 25