Unregulated
aquaculture and invasive alien species: a case study of the African Catfish Clarias
gariepinus in Vembanad Lake (Ramsar Wetland), Kerala, India
K. Krishnakumar 1,
Anvar Ali 2, Benno Pereira 3 & Rajeev Raghavan 4
1 Community Environment Resource
Center, Ashoka Trust for Research in Ecology and Environment (ATREE), Alleppey,
Kerala, India
2,3,4 Conservation Research Group (CRG),
St. Albert’s College, Kochi, Kerala, India
4 Durrell Instituteof Conservation and Ecology, University of Kent, Canterbury, UK
Email: 1 krishnakumar@atree.org, 2 anvaraliif@gmail.com,3 bennopereira@gmail.com, 4 rajeevraq@hotmail.com
(corresponding author)
Date
of publication (online): 26 May 2011
Date
of publication (print): 26 May 2011
ISSN
0974-7907 (online) | 0974-7893 (print)
Editor: Neelesh Dahanukar
Manuscript
details:
Ms # o2378
Received 30
December 2009
Final received 05
April 2011
Finally accepted 20
April 2011
Citation: Krishnakumar, K., A. Ali, B. Pereira & R. Raghavan
(2011). Unregulated aquaculture and invasive alien species: a case study of the
African Catfish Clarias
gariepinus in Vembanad Lake (Ramsar Wetland),
Kerala, India. Journal of Threatened Taxa 3(5): 1737–1744.
Copyright: © K. Krishnakumar, Anvar Ali, BennoPereira & Rajeev Raghavan 2011. Creative Commons
Attribution 3.0 Unported License. JoTT allows unrestricted use of this
article in any medium for non-profit purposes, reproduction and distribution by
providing adequate credit to the authors and the source of publication.
Author
Details: K. Krishnakumar is a Programme Officer with the Community Environment
Resource Center (CERC) of the Ashoka Trust for Research in Ecology and
Environment (ATREE), Alleppey, Kerala, India. His interest is in understanding
biological invasions in freshwater systems of Kerala. Anvar Ali is a
Senior Fellow at the Conservation Research Group, St. Albert’s College, Kochi, Kerala, India interested in freshwater fish taxonomy. Benno
Pereira is a Senior Fellow and Director of the Conservation Research
Group, St. Albert’s College, Kochi, India. His
research interests are in biology and captive breeding of endemic freshwater
fishes. Rajeev Raghavan is a Senior Fellow and Associate Director of
the Conservation Research Group, St. Albert’s College, Kochi,
India. His interest is in conservation biology with special reference to
freshwater fishes of Western Ghats.
Author
Contributions: KK carried out the
field surveys and sampling associated with the study; AA and BP carried out the
biological analyses; RR and AA planned and designed the study, interpreted the
results and wrote the manuscript.
Acknowledgements:The authors thank the local fishers
in Vembanad Lake for their help and assistance during the sampling. The first
author thanks Priyadarsanan Dharmarajan (Fellow), Latha Bhaskar (Project
Coordinator), Seena Narayanan (Research Associate), Aneesh A (Research
Associate) at the Ashoka Trust for Research in Ecology and the Environment
(ATREE), Bangaluru, India for their support. Two anonymous reviewers greatly
improved the manuscript.
Abstract: Indiscriminate and illegal farming of the African
Catfish Clarias gariepinus, in central Kerala has now resulted in the escape and
spread of the species into Vembanad Lake, a large brackish water wetland and
inland fish diversity hotspot. We
collected 17 individuals of C.
gariepinus ranging in size from 200 to 750 mm
from different locations in the southern sector of the lake during a field
survey conducted in 2007. Samples
comprised of mature specimens of both sexes indicating their reproductive
potential in the study area. The
possible impacts of spread of C.
gariepinus into natural water bodies of
Kerala, especially the Vembanad Lake, and options for their management are
discussed.
Keywords:Aquaculture, Clarias gariepinus, exotic fish, introduction, illegal farming, invasive
alien species, Vembanad Lake
For
figures, images, tables -- click here
INTRODUCTION
Aquaculture has been a major cause for introduction of exotic fish
and shellfish worldwide (Naylor et al. 2001). Around 50 species of finfish that are alien to one nation or
the other are being cultured in Asia (de Silva et al. 2006). These include species that are farmed
in accordance with national laws and regulations as well as those that are
illegally introduced and cultured. India, the second largest aquaculture producer in the world (FAO
2008-2009), has a thriving industry focusing on various cyprinids, freshwater
prawn and marine shrimp. Around
40% of the national production is also contributed by various alien cyprinids,
notably the common carp and different species of Chinese carps (de Silva et al.
2006). However, unregulated
introduction and illegal farming of several new exotic species has been
documented in the recent past (Raghavan & Prasad 2006; Singh & Lakra
2006). Several of these species
are listed as potential pests, capable of negatively impacting the native
aquatic biodiversity.
One such species is the African Catfish Clarias gariepinus, which is now widely
farmed in many regions of Africa, Europe and Asia. Clarias gariepinus was brought to India from neighbouring
Bangladesh (Thakur 1998) and cultured initially in the two northeastern states
of West Bengal and Assam and the southern state of Andhra Pradesh, together
with the Indian Major Carp (Baruah et al. 1999). Serious losses to the carp in such mixed culture ponds led
farmers to switch over to monoculture of this predatory catfish (Baruah et al.
1999). The first consignment of
catfish fry from Bangladesh via Andhra Pradesh reached the southern Indian
state of Kerala in 1993 or early 1994 (Middendorp 1998), and since then it has
been cultured in many parts of the state. One important area for African Catfish farming in Kerala has been in the
vicinity of the Vembanad Lake in central Kerala – a region having a long
history of fisheries-related activities, including inland capture fisheries and
aquaculture.
Local fishers have reported stray catches of C. gariepinus from the many waterways
that lie adjacent to the Vembanad Lake since the last decade (Gopi 2000). However, in recent years, increasing
catches of C. gariepinus have been made from the main water body of the lake (K. Krishnakumar
pers. obs.). Therefore our prime
objective was to determine whether C. gariepinus has established a feral
population in the Vembanad Lake, and if so what the repercussions could be for
native ichthyofauna.
METHODS
Study area: The Vembanad - Kol wetland system (09000’-10040’N
& 76000’-77030’E) and its 10 associated drainage
basins are situated in the humid tropical region on the south west coast of the
Indian peninsula. They are
characterized by a continuous chain of lagoons or backwaters, 96km long, one of
the largest estuarine systems in Kerala (WWF 2006). The wetland system covers an area of 1512km2 and
has been designated as a Ramsar Site. The lake is renowned for its live clam resources and subfossil deposits,
as a habitat for the threatened Spot-billed Pelican Pelicanus
philippensis, large bird population especially water fowls, besides a high
species diversity of finfish and shellfish (WWF 2002). One-hundred-and-fifty species of fish belonging to 100 genera and 56 families are known to
occur in Vembanad Lake (Kurup & Samuel 1985).
Sampling and analyses: Detailed sampling was carried out during January
to July 2007 at three sites located in the southern sector of Vembanad Lake
(Fig. 1): Kaithapuzha Kayal, AC Canal and Punnamada Lake (Image 1). The sites were chosen based on the
reports of local fishers on the netting of C. gariepinus in these regions.
Experimental fishing was carried out at dawn (0500-0900 hr) and also during the
night (1830-0000 hr). A variety of gear including gill net, cast net, hook and
line, and scoop net was used to avoid any sampling bias. In order to determine
the relative robustness or degree of well-being of this exotic fish caught from
Vembanad Lake, the coefficient of condition was calculated using the formula K=
100000L/W3 (Williams 2000).
RESULTS
We collected 17 individuals of C. gariepinus (Image 2) in the length
group of 200 to 750mm (total length) from the different sampling sites (Table
1). Fourteen individuals (82%)
collected from the lake had a coefficient of condition (K) greater than one (K
> 1) indicating that the species is performing well in this new habitat and
that it could turn invasive in near future, because it will increase in numbers
and start dominating the fish populations. Catches comprised of both sexes although the ratio was
skewed in favour of females. Three
individuals were identified as mature (2 males and 1 female) based on the
development of testis and ovary which was observed
after dissecting the specimens. All catches of C. gariepinus during our study were made from a hook and line baited with flesh
and intestine of sardine. Ten
individuals were caught during the early hours of the morning (0500-0700 hr)
and seven during the night (2100-2300 hr). Although a wide variety of fishing gears were used, we could
collect C. garipeinus using only a hook and line.
DISCUSSION
Kurup et al. (2004) reported the occurrence of C. gariepinus in farms of Kuttanad
located along the Vembanad Lake in central Kerala. These farms could be the major source of C. gariepinus escapees into the
Lake. The African Catfish has a
tendency to leave the water at night using its strong pectoral fins and spines
in search of land-based food (Burgess 1989) and also move into the breeding
areas through very shallow pathway—movements whichmay be responsible for the fish being widely distributed in the Lake. The most obvious factor that could be
attributed to the escape of pond reared individuals
into the Lake is the physiographic nature of the region. Kuttanad is one of the highest flood
prone areas in Kerala and most of the region is under flood
waters of Vembanad Lake and its confluent rivers during the
monsoon. Most farms in Kuttanad
are traditional ones with little or no infrastructure (Image 3). Ponds are generally shallow and located
in low lying areas adjoining the lake. Monsoon rains
and associated flooding cause bunds and associated traditional sluice
structures in the ponds to break frequently thereby facilitating the escape of
the pond fish into the main water body of the lake. Such escapes are a common yearly occurrence in flood plains
of the Chao Phraya River basin in central Thailand (Na-Nakorn 1999; Seenanan et
al. 2004) where a thriving aquaculture activity of catfish takes place. Another important, but often overlooked
reason for introduction of C. gariepinus in Vembanad Lake and its confluent waterways is the flourishing
live fish trade. Several hundred
large and small fish markets and landing centers are located along the banks of
the Vembanad Lake where C. gariepinus and other native catfish are sold live. As with aquaculture farms in the region, landing centres and
markets are mostly traditional with little or no infrastructure to support live
fish trade. An added worry is the
lack of knowledge on handling practices for live fish by the traders. Such markets and landing centres are
hence a potential source from where C. gariepinus could escape into the lake.
Although aquaculture of C. gariepinus is banned in India vide the
9 October 1997 meeting of the National Committee for the introduction
(screening/observing) of species (aquatic forms) (Gopi & Radhakrishnan
2002), aquaculturists have taken little consideration for such bans and
continue rearing this catfish. It is widely believed that the popularity for
African catfish aquaculture is due to the simplicity in their rearing (Singh
& Lakra 2006). The low
operational costs and high profits derived from African catfish farming have
led to intensification of production. The most common strategy used to augment production is to increase the
rearing density. Some farmers maintain very high stocking densities, higher
than the carrying capacity of the ponds thereby aiding in escapes (Pascal et
al. 2009).
The little or no management measures taken by farmers especially
in preventing such escape of pond reared individuals has now resulted in the
species being distributed in many natural water bodies of the country. C. gariepinus is now being increasingly caught from many rivers including Ganga,
Yamuna, Sutlej and Godavari (Mishra et al. 2000; Sugunan 2002). An unconfirmed report (Basheer 2003)
mentions that the fish is now commonly caught by fisherman in
Periyar River, Kerala, which incidentally is one of the confluent rivers
of the Vembanad-Kole wetland. Gopi
& Radhakrishnan (2002) reported on the negative impacts of the introduction
and culture of C. gariepinus on the native fish fauna of Manalur in Kerala. They observed that African Catfish
escaped from rearing ponds in the area and got established in the larger
community/village ponds subsequently wiping out the indigenous species like
snakeheads (Channa sp.). Apprehensions
have been raised by local communities on the possible impacts to native fishes
of the Kole-wetlands that lie adjacent to ponds stocked with C. gariepinus in the case of such escapes
(Gopi & Radhakrishnan 2002). African Catfish has also been observed from Periyar Lake in Kerala
(Periyar Foundation 2006; Sudhi 2009), a hotspot harbouring many strictly
endemic and Endangered native species (Lepidopygopsis typus, Nemacheilus menoni,
Crossocheilus periyarensis, Hypselobarbus periyarensis, Garra periyarensis, Nemacheilus periyarensis). Vembanad Lake and its associated
wetlands could provide the perfect habitat setting for C. gariepinus to invade and colonize as
they are similar to the natural habitats of this species in Africa—calm
lakes, rivers and swamps in areas that flood on a seasonal basis. C. gariepinus is a slow-moving,
omnivorous predatory fish, which feeds on a variety of food items from
microscopic zooplankton, to fish half its length, or 10% of its own body weight
(de Graff & Jansen 1996). They
are also known to occasionally prey on reptiles, amphibians and birds (de Moor
& Bruton 1988). Vembanad Lake
is an exceptionally rich wetland harbouring many species of aquatic organisms
as well as amphibious reptiles and birds which could be
potential prey for the catfish.
Another important aspect of predation by C. gariepinus is their ability to switch
feeding from one type of prey to another (de Graff & Jansen 1996). This could indicate a grave threat to
all organisms that fall under the prey spectrum of C. gariepinus in case of a proliferation
of population of this exotic catfish in Vembanad Lake. The presence of C. gariepinus in Vembanad Lake is
especially a threat to highly prized native cichlids like Etroplus suratensis and Etroplus maculatus which resembles African
cichlids that are common prey of C. gariepinus in its native ranges in
Africa (Winemiller & Kelso-Winemiller 1996). Vembanad Lake is also home to many species of freshwater and
estuarine catfishes including Wallago attu, Mystus vittatus, Ompok
bimaculatus and Heteropneustes fossilis that share similar trophic niche with C. gariepinus. As with the African Catfish, most native catfish are also
carni-omnivores thereby indicating the possibility of increased competition for
food resources. In addition,
several omnivorous catfishes of Vembanad are listed as threatened due to their
low abundance and declining populations (Molur & Walker 1998). Such vulnerable species are
particularly at risk due to the possible invasion of the ecosystem by a
predator in the class of C. gariepinus. Introduction and
subsequent colonization of C. gariepinus in new environments have led to decline and extermination of local
species. Depletion of 56 species of native fish in Bangladesh has been linked
to the introduction of C. gariepinus (Barua et al. 2000). Similarly, hybrid Clarias (C. gariepinus x C. macrocephalus) is known to have
contributed to the decline of native C. batrachus in the Mekong Delta
(Welcomme & Vidthayanon 2003).
Our collections included at least three mature specimens (one
female and two male) suggesting that the resident population has reproductive
potential. Literature indicates
that C. gariepinus can be sexually active from the first year of its life (Yalcin et
al. 2001). Since the physiography
and eco-biology of the Vembanad Lake including a seasonal monsoon is highly
conducive to the natural breeding of C. gariepinus, it would not be long
before the species breeds establishing a self sustaining population and
subsequently colonizing the ecosystem. Apart from bio-ecological impacts, the invasion of African catfish in
natural waters can also have long lasting genetic implications C. gariepinus was introduced into
Thailand for hybridizing with the indigenous C. macrocephalus. The hybrid is now
cultured extensively and is preferred by local farmers, because of its
considerably higher growth rate than that of the indigenous species and
desirable flesh quality (Na-Nakorn 1999). However, Senanan et al. (2004) and
Na-Kakorn et al. (2004) observed the introgression of African Catfish genes
into the native walking catfish C. macrocephalus in four wild and two broodstock populations in central
Thailand. Native gene pools of C. macrocephalus was suggested to have been
diluted and threatened, and if in the absence of appropriate management
strategies the indigenous walking catfish could be potentially threatened as a
result of massive backcrossing with hybrid catfish (Na-Nakorn et al.
2004). Similar problems have
occurred in Bangladesh through the use of hybrid C. batrachus x C. gariepinus for aquaculture (Rahman et
al. 1995). C. gariepinus in India has been suggested to be a mix of different stocks
belonging to different genetic lineages (Lal et al. 2003).
We positively believe that C. gariepinus has established a feral
population in Vembanad Lake and its associated
wetlands. One
reason for the nonappearance of this species in local fisherman’s catches is
due to the fact that C.
gariepinus is known to seldom entangle in a gill net – which
incidentally is the single most important gear used by local fishers in the
region. Local fishers and
aquaculturists having years of experience with inland catfishes have opined
that African catfish have a tendency to break the gill nets which are laid
overnight and so are conspicuously absent in gill net catches. The extent of spread of C. gariepinus in various natural water
bodies of Kerala especially those that are located near areas where farming of
this species takes place require comprehensive investigations. Vembanad Lake is
an area that needs a more detailed focus as many small and large farms and live
fish markets where C. gariepinus are handled occur in the vicinity of the lake as well as its
confluent rivers. Determining the biological, demographical and genetic impacts
of the presence and possible colonization of this predatory species on native
fish fauna is an immediate research priority. It would also be worthwhile to conduct studies to determine
the best techniques for capture and control of this predator.
The opportunistic strategy and ability to establish large and
persistent populations makes C. gariepinus a threat to native fishes and livelihoods of inland fishers. Thus there is an immediate need for all
stakeholders involved to discuss and deliberate the potential impacts of this
problem and chalk out efficient strategies to combat them. Effectual control of alien species can
only be undertaken through understanding the pathways of introduction and
dispersal. In the case of Vembanad Lake, it is known that aquaculture ponds as
well as live fish trade in the region are the two major sources of
escapes. These pathways can
therefore be regulated to an extent if the authority’s commitment to protecting
native biodiversity is enhanced and the inability or unwillingness to enforce
laws that exist is looked into. Fugitive fish - those that escape from aquaculture facilities (Naylor et
al. 2005) are a major cause for worry in salmon aquaculture. However, solutions including use of
sterile animals and triploids (Benfey 2001; Sadler et al. 2001) are being tried
to mitigate impacts due to the emerging issue of aquaculture escapees.
Effective management requires the availability of relevant
background information. It is true that the ability to understand the problem
of exotic species invasion in Kerala’s inland waters has been extremely
limited. Very little information
is available on the occurrence and possible impacts of exotic species in the
region (Raghavan et al. 2008). A
healthy synergy is generally absent between scientists and policy makers in
Kerala. A common caveat that has
been put forth by policy makers from developing management plans and enforcing
regulations is the lack of information on the occurrence and possible impacts
of exotic fishes in Kerala. We
expect that our present effort could be a start to more studies in the future
that could bring insights into the emerging issue and compel the authorities to
act in a rational manner.
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