become a chain of reservoirs and others
are envisaged for its upper and middle
sections. There are, however relatively
few dams in the large Amazon and Orinoco
basins at present. This is why appropriate
measures from properly planned stepwise
construction should be,formulated now to
avoid the problems prevailing in the other
basins mentioned (Quir6s 1989).
The measures adopted to mitigate the
loss of ichthyofauna due to the construc-
tion of dams and other obstructions in-
clude fish passes in the dams and periodic
stocking of waterbodies with fingerlings
produced in hatcheries. In Brazil, there
is a law providing for the installation of
fish passes (Quirk 1989). In practice,
however, very few have been installed in
Brazilian dams or in the rest of Latin
America, and their e,ffectiveness and eco-
nomic feasibility are controversial. Intro-
duction of exotic species to lakes and
reservoirs also has important impacts. In
Cuba, production of fishes in reservoirs
derives entirely from exotic species: 90%
from tilapias (Oreochronzis aureus, 0.
mossambicus) and the rest from cyprinids
(Cyprinus curpio, Ctenopharyngodon
idella, Aristichthys nobilis,
Hypophthalmichthys molitrix). InMexico,
six main groups of fishes are produced in
reservoirs, four native (Chirostoma spp.,
Chirostoma estor, Ictalurus punctatus,
Micropterus salrnoides), and two exotics
(tilapias and cyprinids) represent 80% of
the total catch (Olmos, in press). In the
northeast of Brazil, two-thirds of the
production through culture-based fisher-
ies in reservoirs is from introduced spe-
cies, both nonindigenous from other ba-
sins (Cichla ocellaris, Cichla temensis,
Plagioscion squamossisimus, Plugioscion
surinamensis,Arapaimagigas, Colossoma
macropomum, Astronotus ocelatus,
Macrobrachiurn amazonicus), and exotics
(tilapias and cyprinids) (Studart Gurgel,
in press).
Fish introductions to the region and
fish transfers among basins have been
reviewed by Welcomme (1988). There is
no rational policy on introductions and
follow-up control, but further progress in
the development of extensive aquaculture
activities in these waterbodies will obvi-
ously improve awareness of the need for
this. Less than 10% of the estimated
potential area for culture-based fisheries
of Latin American lakes and reservoirs is
being exploited at present. Some success-
ful examples are Cuba, 16,000 t (1986);
Brazil, 19,000 t (1987) from over 100
reservoirs in the northeast; and Mexico
109,000 t (19871, which constitutes almost
half the total freshwater aquaculture
production in the region (Juarez, in press).
In these successful cases, different
organizational strategies were adopted.
For Cuba, there is a government-owned
company (Ernpresa Nacional de
Acuicultura), that integrates all the ac-
tivities from research to development. This
has avoided any problems of legal compe-
tence among organizations, and has al-
lowed efforts to be concentrated on tech-
nical and social issues. Three components
ofthe development process which are often
neglectedin other countries receive in this
case the attention they deserve: previous
studies of resident fauna and limnology,
fisheries resources management, and
general follow-up procedures. Studies are
carried out to establish when, which species
and how many fish to stock and how best
to regulate fishing effort, organize groups
of fishers and guarantee sales of the
produce to another government-owned
company which commercializes it.
This integrated form of management,
which includes the operation of a network
of hatcheries to produce the seed (mostly
for tilapia), has led to a wide variety of
basic studies. For example, studies off sh
parasites suggestingoptimal times for fish
stocking (Vinjoy 1988); studies of abun-
dance of fish predators, some of them
introduced species, and work on their