Download River Invesion

Invasion in our Rivers
Text: Unmesh Katwate, Deepak Apte, and Rupesh Raut
W
trade and bio-control of mosquitoes are major ‘vectors’ of
non-native exotic fish species. Cumulative impacts of exotic
fish species are resource competition and predation and niche
overlap that results in an ecological havoc, like species
extinction.
West flowing rivers of the northern Western Ghats are its
least studied biomes. While exploring rivers of northern Western
Ghats in December 2011 at Gadhi river in Panvel, Maharashtra,
we angled a huge pomfret-like silvery fish, later identified as
Red-belly Pacu Piaractus brachypomus. Subsequently, we collected
eight full grown Piaractus brachypomus in the main river channel.
Pacus are commonly found in aquarium shops and have a high
demand in the international aquarium trade. Detailed
investigation revealed that in Panvel area Red-belly Pacu were
commonly preferred for aquaculture. It is likely that the presence
of Pacu in the wild is from an accidental release of aquaculture
stock. Interaction with local fishermen revealed that sighting
of Pacus increased from 2010. Incidentally, locally known as
Riverine Pomfret, Pacu are now commonly sold for food.
UNMESH KATWATE
estern Ghats, a biodiversity hotspot harbours a rich
freshwater fish diversity, which currently totals 290
species. With around 189 species, the endemic
freshwater fish fauna of this region is remarkable. The IUCN
Red List assessment of freshwater fishes of the Western Ghats
indicates that the native and endemic fish fauna are far more
threatened than the non-endemics. Around 97 freshwater fish
species of the Western Ghats were found to be Critically
Endangered, Endangered or Vulnerable. Deforestation,
drainage alteration, pollution, increased urbanisation and
industrialisation, damming, fishing and overharvesting, the
major threats, ensure that this list continues to grow. Besides
these, invasive alien fish species are one of the emerging
potential threats to the natives of the Western Ghats. Invasives
are found to be the second major cause of extinction of
endemic and native species around the world. Catastrophic
impacts of invasive fish species in the Western Ghats are well
documented, but their ecology is poorly studied. Increasing
trade of aquaculture, international ornamental aquarium fish
Diverse tributary of Arjuna river at Ratnagiri northern Western Ghats
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April-June, 2012
April-June, 2012
Red-bellied Piranha Pygocentrus nattereri is popular in the aquarium trade
UNMESHA KATWATE
Another predatory alien species –
Red-bellied Piranha Pygocentrus nattereri –
was recorded by our co-researchers later
from the same area. Aquarium trade is
possibly an important vector for its
release in rivers and associated streams
of Panvel area.
Piaractus brachypomus and Pygocentrus
nattereri are Amazonian natives found in
Colombia, Venezuela, Peru, Bolivia and
Brazil. Introduced populations are
thriving in various parts of the world,
mainly in Far Eastern countries, such as
China and Taiwan wherethey are farmed
for food. Pacu and piranhas are shoaling
fishes and always occur in big shoals in
the wild in the Amazon. Based on gut
content analysis, some researchers report
that pacus and piranhas are herbivores,
but it is well-known that at least piranhas
are voracious predators. Nibbling fins
and scales, biting and giving strong
competition for food resources is
common behaviour of pacus and
piranhas.
The Red-bellied Piranha was first
introduced in Kerala for aquarium trade
in 1999. Recently, in 2011, a scientist
recorded it in Periyar river of Kerala, and
in Dimbhe reser voir near Pune,
Maharashtra, far north in the Western
Ghats.
Multiple cases of bio-invasions have
been recorded in this hotspot, and pacus
and piranhas are the new competitors in
the race for survival of the Western
Ghats fish. A classical and well-known
example is that of the African Catfish
Clarias gariepinus. An escapee from
aquaculture practices, it now dominates
most of the river systems of the Western
Ghats. The exotic C. gariepinus is a regular
in the fish catch of Periyar lake, Kerala.
The introduced population of
Amazonian Pacu in the tropical waters
of Chalakkudy river is also established
and reproducing well. Recent studies on
the endangered Glyptothorax poonaensis, in
Indrayani river, indicates that the African
Catfish may pose a serious threat to its
AJINKYA SAWANT
CONSERVATION NOTES
The sharp-toothed predatory, Amazonian Pacu creates resource compeition for the native species
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UNMESHA KATWATE
CONSERVATION NOTES
An invasive, the African Catfish Clarias gariepinus is spread all over Western Ghats and competes strongly with the native species
Poecilia reticulata are known to threaten the
native Aplocheilus lineatus population
because they share the same niche.
Oreochromis mossambicus – listed in the ‘100
of the World’s Worst Invasive Alien
Species’ – has already spread in most
rivers of the Western Ghats; several cases
of its invasion have been recorded from
different parts of this area. At times, fish
like Catla catla, Cirrhinus mrigala and Labeo
rohita, native to the Ganges river system,
are introduced in greater numbers for
mass aquaculture practices. It is assumed
that these species will not breed in the
ecological conditions of rivers in the
Western Ghats. However, our recent
collection of juveniles of C. catla and
breeding males and females from
Kundalika river, Maharashtra, indicates
that they are breeding easily in our rivers.
Our recent studies in the river systems
of Raigad district, northern Western
UNMESHA KATWATE
existing population. Alien aquarium fish
species introduced purposely or
accidentally into natural waterbodies may
adversely affect native fish species by way
of genetic impacts, disease introduction,
and catastrophic ecological impacts,
such as predation, competition and
environmental modification.
Aquarium fishes like Sword-tail
Xiphophorus helleri, Platy Xiphophorus
maculatus and Guppy Gambusia affinis,
Sun Catfish Horabagrus brachysoma, an endemic of the Western Ghats is threatened by the increasing load of invasives and
exploitation of wild stock for international trade
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April-June, 2012
UNMESH KATWATE
CONSERVATION NOTES
Ghats, suggest that exotics are one of
the major threats for the endemic fish
fauna of this region. We have recorded
nine exotic ‘pest’ fish, i.e. c. 13% of the
total fish fauna.
In more than 20 provinces of United
States countries pacu and piranha are
legally banned for aquarium trade and
aquaculture because of their deleterious
impact on native fish fauna and
ecosystems. Nationwide invasive fish
species eradication programmes are
needed in India to sustain our precious
freshwater ecosystems. Education,
awareness, and spread of scientific
knowledge among locals, aquaculturists
and aquarium traders will hopefully
control exotic species dispersion in
the wild. Strong rules and regulations
should be set for selection of fish
species for aquaculture practice. Use of
endemic species should be promoted
for aquaculture instead of exotic
varieties, reducing the ecological loss of
natural ecosystems. Awareness about
catastrophic ecological impacts of exotic
fishes among aquarium stakeholders,
shopkeepers and buyers will prevent
Unmesh Katwate is
Scientist – A at the Bombay
Natural
History Society.
April-June, 2012
UNMESH KATWATE
(L): Melon Barb Dravida fasciata is a beautiful native barb of the west and east flowing rivers of southern India
(R): Filament Barb Dawkinsia filamentosa is an endemic barb of peninsular India
The vulnerable Ratnagiri Minnow Parapsilorhychus discophorous
is endemic to the northern Western Ghats
further loss. Captive breeding
programmes of native aquarium fish
species may reduce exploitation of the
wild stock and minimize use of exotic
varieties. Scientific monitoring of spread
of invasive alien fish species to implement
and achieve conservation goals is the need
of the hour. Effectively implemented
Deepak Apte is
Deputy Director,
Conservation, at the
Bombay Natural
History Society.
policies are needed to control spread of
exotic alien species in global biodiversity
hotspots. Recent records of predatory
pacus and piranhas have set the alarm bells
ringing for ecological havoc in the Western
Ghats biodiversity hotspot. Should we
ignore them for now or act before it is
too late? „
Rupesh Raut is
Head of the Zoology
Department,
Elphinstone College,
Mumbai.
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