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Home , Fishkeeping, Guppy, Three spot gourami

COMMENTARY

When become pests – exotic and biological invasions in Kerala,

K. Krishnakumar, Rajeev Raghavan, G. Prasad, A. Bijukumar, Mini Sekharan, Benno Pereira and Anvar Ali

One of the major underlying causes for Aquarium is a popular ing large sizes (up to 500 mm) and increased biological invasion is the hobby among many people in Kerala, exhibiting territorial behaviour. Further, growth and development of world mar- where the demand for exotic is they are capable of tolerating pollution kets1 facilitated through globalization, maintained by the supply from commer- because of their air-breathing ability22 and the booming intercontinental trade of cial breeders and farmers operating both and are also known to create serious nega- live flora and fauna. The vast majority of within and outside the state. There are tive impacts on periphyton feeding and recent invasions has been attributed to around 168 registered aquarium shops bottom spawning fishes. Similar situa- human activities associated with this operating in the state15, and many hun- tions may be replicated in water bodies international trade, which is accelerating dreds of unregistered ones. With around of Kerala, where economically valuable the spread of organisms into new re- 500 breeding units, Kerala is also the bottom spawners such as Etroplus surat- gions2,3. Global trade in flora and fauna third largest ornamental -producing ensis occur. Grazing on benthic has led to both repeated introductions of state in India16. To a large extent, the and by suckermouth is popular exotic species in many systems breeding and rearing of exotic aquarium also known to alter and reduce food, and and has aided in secondary releases fish in Kerala are carried out in earthen physical cover available for various through their cultivation4,5. For example, and cement , cement tanks and aquatic insects23, thereby affecting the in the United States, 85% of established plastic lined pools. Many hundreds of trophic chain. The perennial ponds from non-native woody species were in- species of exotic aquarium fish are bred where P. multiradiatus were collected troduced through horticultural trade6, and in such systems and marketed in the state. from Vylathur, are connected to the 26% of non-indigenous freshwater fishes Despite this extensive trade, release and Canoli canal which is subjected to tidal that occur beyond their native range were dispersal of exotic aquarium fish, and its influx from the adjacent backwaters18. introduced through the aquarium trade7. consequences on native species and eco- Hence, the possible escape and coloniza- Over one billion ornamental fish com- systems is yet to receive attention in the tion of the sucker catfish in the back- prising more than 4000 freshwater and state. waters and associated natural waters of 1400 marine species are traded interna- Eleven species of exotic fish are the region is a cause for grave concern. tionally each year8, making it one of the known to occur in the inland waters of P. multiradiatus has also established a most important components of the global Kerala17, posing a serious threat to the substantial population in Chackai Canal, fish trade. Freshwater species make up native . Of this, at least four replacing other herbivorous fishes21. 90% of this trade as they are the most species are popular aquarium pets: Ptery- Apart from biological interactions, P. popular and widely kept aquarium pets goplichthys multiradiatus18 (algae multiradiatus is also known to cause worldwide. Although aquarium fisheries sucker/sucker cat), reticulata19 economic losses to fishermen through and trade is a multi-million dollar indu- (), Trichogaster trichopterus20 damage to gears, especially cast stry that supports thousands of rural peo- (three-spot ) and and gill nets24. ple in the developing countries, as well maculatus19 (platy). Individuals of guppy, P. reticulata, as retailers and hobbyists in developed P. multiradiatus, an armoured catfish one of the most popular aquarium fishes countries, the industry is also known to native to the South American drainages, worldwide were collected from the second be one of the most important, yet poorly is a popular aquarium worldwide and order streams of Chalakudy River flow- studied pathways for biological invasions is known commonly as ‘’. P. ing through tea plantations19. Many were in aquatic environments9. The release multiradiatus has been recorded from found to be brooders, whereas others were and dispersal of aquarium fish have re- three natural freshwater ponds at Vyla- early fry, suggesting that P. reticulata ceived little attention worldwide10,11, in thur in Thrissur District18, and the has already established a self-sustaining spite of the knowledge that one third of Chackai Canal of Thiruvananthapuram population in these waters. Further, gup- the world’s worst aquatic invasive spe- District21 in Kerala. Species under the pies have established good populations in cies are ornamentals12. Aquarium fishes genus Pterygoplichthys have been intro- natural ditches connecting the main are mainly introduced into recipient duced worldwide as a result of the orna- branches of Meenachil River in Ay- waters as a disposal method apparently mental fish trade. In the , manam Panchayat in Kottayam District25 perceived as more humane than various where they are known as janitor fish, two and also in the drainage canals of Erna- euthanasia options13. The most com- species have established feral popu- kulam city, which are connected to various monly cited reasons for release of healthy lations in Marikana River and Laguna de natural water bodies including the Vem- ornamental fish are that owners tire of Bay, and are considered a threat to the banad Lake. Since males of P. reticulata them, or that, they become too large or native freshwater fish. P. multiradiatus is mature at two months and at prolific for their aquaria14. Additional also known to have established in natural three months of age, they have every reasons include accidental escape during waters of countries as widespread as chance of proliferating and becoming a drainage of water from aquaria9 and dur- Puerto Rico, United States of America potential pest in the inland waters of ing rains and floods from culture systems. and Taiwan. They are omnivores, attain- Kerala.

474 CURRENT SCIENCE, VOL. 97, NO. 4, 25 AUGUST 2009 COMMENTARY

Another recent study20 resulted in the our understanding on the alien fish inva- Although the National Committee for collection of 21 individuals (15 males sion in Kerala is through a handful of Exotic Species suggested setting up of and 6 females) of the popular aquarium studies restricted to certain rivers17,19,20. quarantine facilities for the import of fish, T. trichopterus – , Unless follow-up investigations are con- aquarium fishes near the international from canals that empty into Vembanad ducted over subsequent years, the status airports38 at Mumbai, Chennai and Kol- Lake – the first report of this species of many exotic invasions will remain un- kata as early as 2004, there has been no from natural waters of Kerala. The habi- known. Multiple discoveries of various concerted effort to implement such a tat from where T. trichopterus was col- life stages over at least two consecutive policy till date. Exotic species introduced lected was also seen to be infested with years could reveal the establishment po- purposefully or accidentally into natural Eichornia crassipes, a common invasive tential of the species in various river sys- water bodies can adversely affect local waterweed. Local fishers also revealed tems. Large populations of P. reticulata fauna through genetic pollution, disease that gourami have been sporadically ob- and X. maculatus which have been obser- introduction and ecological impacts, such served in their catches since the last few ved continually over the last few years in as , competition and environ- years. The length–weight relationship of Chalakudy River confirm fears of their mental modification. More precaution is T. trichopterus revealed a positive iso- widespread invasion in this riverine hot- essential while undertaking large-scale metric growth indicating that the species spot. breeding programmes of exotic ornamen- has a good condition in this habitat20. Al- Marketing and trade in exotic aqua- tal fish. Effective quarantine measures though there is no information on the rium species is significantly related to are required as a precaution to prevent ecological impacts of the three-spot their occurrence and establishment in the the introduction of pathogens and para- gourami in its introduced ranges, the wild. The volume of trade in many spe- sites along with exotic species, and to species is an opportunistic hav- cies is known to be a significant factor in reduce the resultant economic losses to ing territorial and aggressive behaviour26 the probability of their establishment29. the country. that could potentially prove harmful to Fish species sold in high volumes in the Aquarium fish trade is undeniably a native ornamental species such as Pseu- aquarium trade are more likely to be vector activity that has a role in the dosphronemus cupanus and Apolocheilus sighted in the wild11,30. ‘Propagule pre- introduction, dispersal and invasion of lineatus. ssure’ – still the best explanation of inva- exotic species. The role of domestic The insectivorous feeding habit of sion success31,32 has been used as a basis markets and local trade in the dynamics platy, Xiphophorus maculatus makes them to understand the dynamics of invasion of invasion success needs to be studied potential competitors for indigenous of many species in different coun- in detail as the escape, establishment and barbs like Puntius fasciatus, Puntius tries11,33,34. The four species of exotic spread of exotic aquarium fishes will ticto, Puntius vittatus and Killi fishes fish sighted from the wild (P. multiradia- depend on the developments in domestic like A. lineatus, A. panchax and A. dayi. tus, T. trichopterus, P. reticulata and X. markets33. In addition, field investiga- As in the case of P. reticulata, X. macu- maculatus) are indeed some of the most tions on eco-biology of the exotic fish latus also attain sexual maturity popular and intensively marketed orna- species that have established in the wild after 3–4 months and reproduce easily, mental varieties in Kerala, giving credi- should be carried out, in an attempt to becoming potential pests in the near bility to the propagule pressure effect. manage the existing invasive popula- future19. A. lineatus, which is a popular Another major risk factor is the rearing tions. This will allow fisheries research- native ornamental Killi fish species of exotic aquarium fishes in open sys- ers and conservation biologists to control found in Chalakudy River27, was found tems such as granite quarries and home- any additional dispersal of exotic fish to to co-exist with X. maculatus in the mid stead ponds. Quarry farming of orna- new , and limit the impact and upstream reaches (Rajeev Raghvan, mental fish is an emerging activity in that these exotics may have on the native pers. obs.). Platy is already known to Kerala, especially in the central dis- fauna with regard to predation, competi- have become sympatric with the native tricts35. During monsoon, water accumu- tion for food and other resources, and melon barb, Puntius fasciatus in the first lates in the quarries and the owners lease also introduction of new pathogens. order streams of Chalakudy River28. their sites for ornamental fish culture. A Although not all aquarium fish species vast majority of such quarries are not released/escape to the wild will survive, protected with fencing/netting, and as a 1. Mooney, H., Assessment and Manage- nor will all of those that survive be able result, individual fish escape into the ment of Alien Species that Threaten Eco- to reproduce or ultimately become pests. adjoining natural during systems, Habitats and Species, CBD If sufficient numbers of individuals runover associated with monsoon. Simi- Technical Series 1, Secretariat of the find their way out, they may be able to lar problems also exist with homestead Convention on Biological Diversity, reproduce9 and subsequently establish ponds culturing exotic aquarium fish. 2001. feral populations. The large populations Such culture ponds operate with little or 2. Perrings, C., Williamson, M. and Dal- of P. reticulata and T. trichopterus ob- no infrastructure to prevent escape of mazzone, S. (eds), The Economics of served from Chalakudy River and Vem- captive fish during monsoon, when there Biological Invasions, Edward Elgar, Cheltenham, United Kingdom, 2000. banad Lake are evidences for species that is considerable flooding. 3. Mack, R. N. and Lonsdale, W. M., Bio- have now established in the new environ- To make matters even more compli- Sci., 2001, 51, 95–102. ments. Little information is currently cated, India has no legislation on the 4. Levine, J. M. and D’Antonio, C. M., available on the distribution and import or introduction of aquatic orga- Conserv. Biol., 2003, 17, 322–326. 36 possible impacts of other exotic aquar- nisms , nor is there a proper quarantine 5. Mack, R. N., Biol. Inv., 2000, 2, 111– ium fish species in the region. Much of procedure in place for imported fishes37. 122.

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