Alien fish species in the Bharathapuzha

Thiruvananthapuram: An exotic species of fish, native to Africa and
West Asia, has been discovered in the Bharathapuzha, raising concern
about its impact on the native aquatic ecosystem.A. Biju Kumar of the
Department of Aquatic Biology and Fisheries, University of Kerala,
discovered Nile tilapia (Oreochromis niloticus) while documenting the
biodiversity of the river. It was collected from Chamravatom, Shoranur
and Ottapalam regions. The identity of the species was confirmed by K.
Rema Devi, ichthyologist at the Zoological Survey of India, Chennai,
where the specimens are now deposited.Nile tilapia can be
distinguished from its close cousin, Mozambique tilapia (Oreochromis
mossambica), a very prevalent fish in Kerala, by the dark vertical
stripes throughout the depth of the caudal fin.Tilapias have been
transplanted to many parts of the world for aquaculture. "They are
large, fast-growing and tolerate a wide variety of water conditions
(even marine conditions). Once introduced into a habitat, they
generally establish themselves very quickly. Though predominantly
phytoplankton feeders, in many water bodies, they act as omnivores and
even carnivores. They may spread to a new river system via estuaries
and coastal waters in which they are able to breed," says Mr.
Kumar.Out of the 112 species of fishes collected by the researchers
from the river, the exotic fishes were represented also by the common
carp and Mozambique tilapia. These fishes were found in the Chulliar,
Meenkara and Malampuzha reservoirs and the tributaries of the
river."However, the presence of Nile tilapia in the river comes as a
surprise as this species has not been introduced in the State formally
for aquaculture. Tilapias have already established breeding
populations and hence their negative impacts on indigenous species
should be viewed seriously," Mr. Kumar said. "They could compete with
local species and prey on the eggs and larvae of other fish."
International organisations such as Worldwatch Institute consider
bio-invasion as the second greatest threat to biological diversity,
the first being habitat degradation. When an exotic species
establishes a beachhead, it can proliferate over time and spread to
new areas. It can also adapt — it tends to get better and better at
exploiting an area's resources and at suppressing native species.
Published scientific data on the ecological and economic impacts of
invasion of alien fish species are not available in India. "While the
introduction of exotic organisms is strictly monitored in most other
countries, considering the threat to the local biodiversity and
endemic organisms, quarantine measures in India are inadequate. There
are no legal restrictions or standardised procedures for introduction
and monitoring of species," Mr. Kumar said.The list of alien fish
species invading the natural water bodies of Kerala includes
Mozambique tilapia, rainbow trout, giant gourami, blue gourami, common
carp, catla, rohu, mrigal, guppy, African catfish, sucker catfish,
platies and sword tail.The Food and Agriculture Organisation has named
tilapia as a biological pollutant after several countries reported
adverse ecological impact after the introduction of the species.

The Hindu, 8th December 2008