Environment and aquaculture in developing countries

control with selective fishinggear; studies
on aquatic weeds and their control, includ-
ing the use of herbivorous carps and
mechanical methods; monitoring of pollu-
tion, particularly from sugar and paper
factories, as well as other industrial wastes,
fertilizers and pesticides; absolute control
of species and quantities of fish stocked;
and a genetic improvement program with
tilapia at a research center in Pav6n, Santa
Clara Province (Mari-Diaz, in press).
In the semiarid zone of the Brazilian
northeast, the Departamento Nacional de
Obras Contralas Secas (DNOCS) has been
responsible for the last 40 years for the
fisheries exploitation of 104 reservoirs,
with a total water surface of 140,000 ha
and a mean annual production of 17,000
t. DNOCS also carries out periodic stack-
ing of native and exotic species produced
in their hatcheries. These culture-based
fisheries activities are based on studies of
fish population dynamics and on effort
regulations to limit entry.
There is still controversy on cleaning
of the reservoir bottom before it is flooded.
The policy that prevails is to leave it
untouched in order to offer more fish
refuges and feeding areas, but submerged
vegetation can hamper fishing. For Brazil,
Godoy (1 985) reports 35 structures to assist
fish migration after dam construction of
which 21 are located in the DNOCS area.
With respect to the introduction of species
from other parts of the country or exotic
to the Region, DNOCS's experience is, in
general terms, positive because it has
increased the yield ofcommercially impor-
tant species (Studart Gurgel, in press).
In Chile, the rapidly growing salmonid
culture industry has already attracted
criticism with respect to its impact on the
aquatic environment, particularly fresh-
water lakes, concerningmainly the effects
of wastes and escapes of fishes. Some of
this criticism also questions the esthetic
impact of the activity. Alternative uses of
the environment such as recreation and

tourism do not seem to mix well with fish

farming (Munro 1990).

Much has still to be learned about the

long-term effects of aquaculture. Existing

regulations have been established empiri-

cally based on the quantities of harvested

fish per unit of area. Criteria for the

maximum permitted amounts of solids

and chemical compounds leaving and

enteringaquaculture installations are still

being discussed (see below: Aquaculture

legislation and conservation offreshwater

ecosystems). When rivers carry farm

wastes into lakes, this must be included

in the overall calculations of their carry-

ing capacity for aquaculture. It is very

difficult to collect all the necessary infor-

mation for this, particularly in developing

countries.

Intensive Freshwater

Aquaculture

Intensive aquaculture in the majority

of developing countries is largely aimed

at export markets, although tourism-re-

lated consumption may generate some

seasonal demand. Intensive freshwater

aquaculture in many developing countries

is only just starting to expand; for exam-

ple, trout and smoltproduction in salmonid

culture (Oncorhynchus mykiss, 0. kisutch,

0. tschawytscha, 0. masou, Salmo salar)
   in Chile (Munro 1990) and tilapia culture
   (0reoch.romis aureus x 0. hornorurn) in
   CostaRica (Martinez-Palacios et al. 1989),
   grass carp (Ctenopharyngodon idella) and
   eel (Anguilla juponica) in China (FA0
   1983), snakehead (Channa striatus),
   walking catfish (Clarias spp.) and giant
   freshwater prawn (Macrobrachiurn
   rosenbergii) in Thailand (Boonyaratpalin
   and Akiyama 1989).
   The nature and extent of the environ-
   mental impact of intensive freshwater
   aquaculture, drawn mainly from experi-
   ence by industrialized countries (Alabaster