are usually given in combination with
fresh or frozen fish (some 10% of the total).
In less developed countries, feeding of
carnivores is still very much dependent on
by-catch or low-value marine fish, which
is increasingly in short supply. Fishing
communities engaged in marine fish cage
culture, therefore, often resort to capturing
small-sized juveniles of economically
valuable marine fish species in order to
feed their stocks. Formulated feeds are
also dependent on mnrine protein as they
contain 40 to 70% fish meal. Thus,
carnivorous fish culture is in direct
competition with animal husbandry for
the limited marine protein sources.
Globally about 10% of the total fish meal
production is used in aquaculture feeds
(Pike 1989).
Due to the high stocking densities and
heavy feeding, both cage culture and pond
culture of carnivores are potential sources
of pollution. Hazardous concentrations of
cageslcage farms are seldom controlled by
rules and regulations in the developing
countries of Asia; even if such legislation
exist, its enforcement is problematical.
However, as feeding is based almost
exclusively on fresh fish, the major problem
is organic pollution, which can often be
absorbed by the environment, provided
the site selection is properly done.
Polluted effluents from high density
eel or catfish ponds in inland areas are
more problematical as they usually enter
a common water supply network, from
where they may be reused in neighboring
ponds. Unfortunately, in developing
countries of the region, separate drainage
and irrigation networks rarely exist.
Another potential hazard is the
unchecked (and in most cases
unwarranted) use of various drugs,
primarily antibiotics, in intensive pond
culture of carnivores. Unscrupulous
dealers persuade fish farmers to use these
drugs as preventive measures (forinstance
in Clarias catfish ponds against the
epizootic ulcerative syndrome) with very
dubious benefits but with high risks of
developing more virulent, antibiotic-
resistant strains of pathogens (see Austin,
this vol.).Crustacean Culture
As noted earlier, until1 983 production
of this commodity group did not play a
significant role in Asian aquaculture,
although its share increased from 0.6 to
1.6% ofthe total volume between1975 and- Then a spectacular growth started
(Fig. 3). Between 1983 and 1988, the
average annual growth of crustacean
production was 4196, and by 1990
crustaceans reached 4.5% of the total
volume of cultured aquatic organisms in
the region.
Details of crustacean production in
Asia and the Pacific in 1987 are presented
in Table 11. Out of the 0.7 million t global
output, the region produced 81%. Almost
all came from the developing countries of
Asia. Major producers were China,
Indonesia, the Philippines, Taiwan,
Thailand and Vietnam. Marine shrimp
was the dominant species group in the
region, mostly Penaeus and Metapenaeus
spp. Freshwater prawns contributed 5%
to the regional total and crabs, lobsters
and other marine crustaceans provided
the rest. Production offreshwater crayfish,
which is an important species group in the
rest of the world, is insignificant in the
region, despite marked interest in the
culture of Cherax species in Australia.
As crustacean aquaculture in Asia is
dominated by brackishwater and marine
species, it is primarily a coastal activity.
When comparing the development of
crustacean culture in various countries,
the volume of production per kilometer of
coastline is a suitable indicator (Table 12).
In 1987, Taiwan (the leader in shrimp
culture development) produced 56.7 t of
crustaceans per kilometer of its coastline.