- and rivers of the island of Mauritius (George 1976). Also in Lake Kin-
kony in Madagascar, T. rendalli, accidentally introduced, in three years
devastated nearly 3,000 ha of Ceratophyllum and Nymphaea beds with in
consequence the almost total disappearance of a valuable indigenous fish,
Paretropus petiti (Lamarque et al. 1975).
OTHER REGIONS (see Table 3)
In environments characterized by suitable temperature conditions and
offering a vacant ecological niche, tilapias are able to establish themselves
and form stable populations, contributing to the augmentation of the local
fishery resources (e.g., S. niloticus in Indonesia, Bangladesh and Mexico;
T. rendalli in Sri Lanka and S. mossambicus in Hong Kong).
In most cases, however, the establishment of tilapias in natural waters
has engendered, as in Africa, unfavorable consequences: 1) initial growth
of the population followed by spontaneous regression with some of these
failures (e.g., S. mossambicus in Thailand and Bangladesh and S. niloticus
and T. rendalli in Thailand) resulting from competition from local species
or the influence of unfavorable environmental conditions, which, even if
they do not occur every year suffice to hamper the long-term survival of
the populations; 2) disappointing practical results due to continuous repro-
duction (overpopulation and dwarfing) in equatorial and tropical environ-
ments (e.g., S. mossambicus in Indonesia and T. rendalli in certain Brazilian
lakes) and to slow growth and winter mortalities in regions situated at the
limit of the natural distribution of tilapias (e.g., S. mossambicus in the rice
fields of Taiwan and T. zillii for the biological control of aquatic vegetation
in California and 3) excessive destruction of aquatic vegetation by macro-
phyte-feeding tilapias (T. rendalli in Brazil), damage to the indigenous fauna
(S. mossambicus in Florida and in Colombia), competition for food and
predation affecting other valuable species (S. mossambicus in the brackish
Chanos chanos (milkfish) ponds in the Philippines).
Introductions sometimes prove to be failures in an economic scale as the
species introduced was not accepted by the local population because of its
unfavored taste (S. mossambicus in Thailand, Welcomme 1979b), small size,
or because it was not the most judicious choice to fulfill its assigned role. Con-
sidered as a 'miracle fish' at the time of its first introduction to Southeast
Asia, S. mossambicus has given poor results which explains why this species
is now being progressively abandoned for use in culture: S. niloticus, S.
aureus (Bowman 1977) and various faster growing hybrids with a higher pro-
portion of males are preferred. S. mossambicus is in Asia what S. macrochir
is in Africa.
Finally, the introduction of tilapias (and of exotic species in general) may
assist the dispersal of diseases and undesirable parasites; thus the construc-
tion of tilapia ponds in Puerto Rico has favored the habitat of the molluscan
vectors of bilharzia and this malady may reach Florida (Courtenay and
Robins 1973).
