Exotic Aquatic Organisms - International Development Research ...

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with respect to other introductions. For example the introduction of Lates niloticus into Lake
Victoria was hailed as a disaster by some (Barel et al. 1985; Payne 1987) but its introduction into
Lake Kioga is considered as a success; as much as that of Limnothrissa miodon into Lakes Kivu
and Kariba (Eccles 1985). A similar debate exists with respect to the introduction of
Sarotherodon aureus into Lake Kinneret (Gophen et al. 1983).
The above examples point out that the lack of specific criteria and/or adoption of different
standards in the assessment of the role of an exotic, and focus on the need to establish criteria for
evaluating the impact of an exotic. The evolution of such a scheme for the evaltation of the
impact of exotics will not have a direct bearing on the introductions made hithcrto but will
permit the adoption of a more rational and an objective approach for envisaged introductions.
The system or scale that is to be devised should not only take into consideration the biological
and ecological impact of the introductions but an equal weightage should also be given to the
sociological impact.
Sociological impact is not an easily quantifiable parameter. In the present context it would
mean whether the introductions have resulted in a significant contribution to the protein supply
to the poorer people in an area and/or whether a significant number of job opportunities have
been created or lost as a result of the introduction and the like.
Reported detrimental effects as a result of piscine introductions into Asia, apart from the
numerous parasites associated with the introductions, are rare and far apart; it has never reached
the controversial stage as for example that associated with the Lates niloticus introduction into
Lake Victoria in Africa (Bare! et al. 1985; Payne 1987). However, in Asia aso the near
extinction of the endemic small goby, sinarapan, Mistichthys luzonensis (Smith) from Lake Buhi
is partly attributed to the introduction of 0. mossambicus (Baluyut 1983). Similarly the
introduction of two gobiids into Lake Lanao is supposed to have influenced its native cyprinid
flock consisting of about 20 species of Barbus (Frey 1969). Asia has a paucity of lakes. Hence,
there is an equivalent paucity of species flocks comparable to those of the African Great Lakes.
In this context all efforts must be made to preserve this minuscule number of spec es flocks in
Asia.
The global parasitic introductions associated with the piscine introductions have been
reviewed by Hoffman and Schubert (1984). Asia contributed its share to the rest of the
continents and likewise received its share from elsewhere. It remains a miracl that these
accidental introductions have not reached epidemic levels, except in very rare and isolated
instances. Even human pathogens are involved; for example, Schistosoma mansoni was
transferred to Hong Kong in 1973-1974 in infected snails from South America (Biophalaria
straminea) contaminated with imported water plants for aquaria (Meier-Brook 1975).
All fish trematodes and cestodes require intermediate hosts; digenean trematodes a
molluscan host, and cestodes one or more intermediate hosts. As a result of these requirements
the chances of relocation of parasitic species and their spreading are limited. In spite of these
requirements some parasites have been transferred. A case in point is the inter-continental and
intra-Asian relocation of the cestode Bothriocephalus opsarichthydis (=B. go wkengensis)
associated with the introduction of grass carp, initially from the Amur river stocks and later from
elsewhere.