Exotic Aquatic Organisms - International Development Research ...

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Larvicidal Fish
The poeciliid Lebistes reticulatus was introduced for mosquito control. It is reported that
one more species of larvicidal fish, Notobranchus sp. has also been introduced (Sreenivasan et
al. 1988). However, these fish have not been widely employed for the purpose they were
introduced. On the other hand, Gambusia affinis is known to adversely affect the fishery of other
fishes by preying on their spawn. In Ooty Lake, this fish severely affected the mirror carp fishery
and only after its eradication, the mirror carp fishery could be reestablished.
Ornamental Fish
A large number of ornamental fish, consisting of both egg layers and live bearer;, have been
introduced into the country over the years. Baskar et al. (1988) have reported the presence of 261
species of exotic egg layers in India. However, they contribute about 25% to the country's export
trade, which is dominated by the domestic egg layers. Subramanian et al. (1988) listd a total of
27 exotic live bearers in India. A number of different strains are reported to exist within these.
Exotic aquarium fishes are considered important from the view point of developing export and
domestic trades.
Molluscs
Mytilopsis sallei
This exotic bivalve, which is native to Central American region, appears to have been
brought into Indian waters through ship fouling in the late 1960s. It has become a major fouling
pest, gaining almost monospecific dominance in fouling communities, with a biornass build up
of to 100-120 kg/m-2/yr. This bivalve is also seen in large numbers in Kakinada harbour, but
only to a small extent in Bombay Harbour. It appears highly probable that this fouling organism
will pose a serious problem in the country (Rao et al. 1988).
Aquatic Plants
Over the last century, several aquatic plants have been introduced into the couniry, but a full
list of these is not readily available. However, only a few of them are of importance from a
fisheries point of view in that they have proved harmful. Foremost among them is the water
hyacinth (Eichhornia crassipes), which was reportedly brought from Australia for its flowers.
This fast growing weed has become the single biggest menace in fishery waters and navigation
channels. Even though effective mechanical and chemical methods for eradication of this weed
are known and also practised off and on, failure to take suitable follow-up measures has
invariably led to reinfestation. Its growth is particularly pronounced in waters receivLng domestic
sewage. Recent experiments have shown the possibility of biological control of this weed using
the insect Neochitina eichhorniae (Jayanth 1987). Some recent studies have indicated the
possibility of useful utilization of this obnoxious weed, such as in bio-gas production (Joglekar
and Sonar 1986), and fish feed (Anil et al. 1986).