sedimentation rate (2.0-25.0 g.rrr2.day-l;
mean, 13.3 gm-2.day-l) lower than that
reported for temperate zone cage culture:
e.g., 150 g.mL2.day-I (Merican and Phillips
1985); 17-26 g.mm2.day-l, (Enell and L6f
1983). The reservoir also received about
150,000 m3.day-I of organic wastes from
the Bandung conurbation and the natural
sedimentation rate was 1.7 * 1.2 gar
.day-l. This aquaculture development now
supplies about 20% of the freshwater fish
supply for a conurbation of 3 million
people.
In examining the environmental
impact of, and in setting limits to, the
density and siting of cages based on the
carrying capacity oflakes, it is essential to
balance benefits against any additional
pollutingeffect ofthe cages and to consider
exactly what environmental and social
targets are achievable. Costa-Pierce (1990)
made the general point that the
environmental impact of cage culture in
the Saguling Reservoir was insignificant
compared to the impacts of raw sewage
and of water level fluctuations, which
confound attempts to estimate absorptive
capacity.
Afurther example concerns the use of
chemicals in developing-country
aquaculture. The misuse of antibiotics
and pesticides should be prevented
everywhere. Steroid hormones, however,
against which there is a blanket ban in
food production in some developed
countries, can be used to good effect in
developing-country aquaculture to produce
monosex male tilapias (Guerrero 1982).
There is as yet no comparable practical
method for avoiding the problems of
uncontrolled tilapia breeding. Alternative
methods, suchas hybridization, havemany
disadvantages, e.g., use of additional
(sometimes exotic) species and strict
management requirements. The benefits
from hormonal production of monosex
male tilapia fry (by short-duration
treatment of fry) are clear and the
technique is beginning to be adopted in
some developing countries (Macintosh et
al. 1985). All available evidence suggests
that hormones are eliminated in a few
days and no residues could possibly be left
in fish sold to consumers (Johnstone et al.
1983). Rothbard et al. (1990) even found
that an androgen fed to tilapia for 11
weeks as a growth promoter was also
eliminated in less than a week upon
cessation of treatment. There are some
risks to hatchery workers if they mishandle
androgenic hormones and there are
possibilities of contamination of the fish
farm and adjacent environment (Rothbard
et al. 1990), but clearly it would be unwise
to prohibit entirely techniques, that are
valuable and that can be applied safely,
involving the use of hormones in tilapia
culture in developing countries.
Sewage-fed fish culture affords another
example. The risks may be insignificant,
provided that postharvest handling is
hygienic and produce is well-cooked
(Edwards 1985). In China, India, Indonesia
and Vietnam, large quantities of fish and
vegetables are raised on human excreta.
Excreta reuse through aquaculture may
be one ofthe least environmentally harmful
disposal methods. It should also be more
feasible in developing countries where
sewage wastes and wastewater are less
mixed with detergents, heavy metals and
other chemicals than in industrialized
countries, though this is a worldwide
constraint.
All the above examples show that
technical advice and policy formulation
for aquaculture development must be
attuned to specfic needs andopportunities,
rather than being constrained by foreign
cultural biases. Experience gained in and
technical expertise from developed
countries can assist aquaculture
development with environmental
protection in the developing regions
provided that this requirement is met.