Over 30 exotic species found in Kerala’s water bodies: study


After the devastating floods in Kerala in 2018, several photographs and videos of ‘strange’ fish caught by local fishermen made headlines and were widely shared on social media platforms. This caught the attention of PhD researcher Smrithy Raj studying invasive alien fish at the University of Kerala. Raj is part of the team that has studied freshwater ecosystems across Kerala from 2016 to document the presence of exotic aquatic species.

Their findings, recently published in Health and management of aquatic ecosystems, states that Kerala waters are home to 28 species of exotic fish and four exotic aquatic weeds or macrophytes.

“Exotic species are introduced to India primarily for the purpose of species diversification in aquaculture, the aquarium trade, biological mosquito control and big game fishing. These fish, when they escape into natural water bodies, tend to threaten native biodiversity and disrupt other ecosystem services, ”says Smrithy Raj.

The surveys were carried out in 44 rivers and 53 reservoirs in the state. The most common invasive species identified were Oreochromis mossambicus and Cyprinus carpio.

Also known as Mozambique tilapia, O. mossambicus is native to Africa and can be around 39cm tall and weigh just over a kilogram. It has been found in 44 rivers, 25 reservoirs and two freshwater lakes in Kerala.

Cyprinus carpio, or the common carp, has been cultivated for about 2,500 years and is a popular angling and ornamental fish. According to the International Union for the Conservation of Nature, “C. carpio is the third most frequently introduced species in the world and on all continents where it has been introduced, it has reduced water quality and degraded aquatic habitats.

Entry way

The team noted that of the 32 alien species, 15 were introduced through the aquarium hobby and trade, six species were introduced for the promotion of aquaculture, three for mosquito control and three species for the aquarium keeping or aquaculture promotion.

“The rainbow trout, Oncorhynchus mykiss, was introduced during the colonial period to promote sport fishing, the only species introduced for this purpose,” the newspaper adds.

The maximum number of exotic fish species was recorded in the Chalakudy River, which was home to 11 exotic fish species of which eight species were recorded after the flooding, which includes rare mega-fish like Arapaima gigas.

Another article published by the team in April noted that: “Large-scale flooding in August 2018 and 2019 resulted in the escape of at least ten species of exotic fish that were first recorded from natural waters of the Western Ghats “.

One of the authors of the article Rajeev Raghavan from the University of Fisheries and Ocean Studies of Kerala explains that several illegal farming systems could have facilitated the escape of exotic species. “With the increase in extreme weather events, we could see the spread of more alien or non-native species in the state. There must be control over illegal aquaculture in Kerala which is now operating for aquarium purposes.

He adds that there is an urgent need to study the entry route for these alien species and perhaps use biosecure fences near hatcheries that raise non-native species. When asked if there was a method to remove these invasive fish from water bodies, he said: “Recently, the Periyar Tiger Reserve launched a campaign to eradicate the African catfish in the lake. Periyar. Authorities noted that more than 450 kg of African catfish were caught in three days. Maybe we can try this initiative on a larger scale, but it would be impossible to fully fish them out. “

Invasive plants

The team documented four macrophytes or aquatic weeds in the water bodies of Kerala – Salvinia molesta, Pistia stratiotes, Eichhornia crassipes and Cabomba furcata. The first three plants were introduced as garden plants or for research promotion. The team writes that their entry into natural systems would be accidental.

Cabomba furcata may have entered natural water bodies either from domestic aquariums or from ponds used for breeding aquarium plants.

“A few organizations are now trying to make value-added products using these invasive weeds. They can be used as manure, wet material for mushroom cultivation and for the production of a multitude of value-added products. If we can find a commercial target for these weeds, we may be able to slowly eradicate them from our waters, ”says Appukuttannair Biju Kumar, from the Department of Aquatic and Fisheries Biology at the University of Kerala and corresponding author of the work.

How to manage aquatic invasive species?

The team notes that scientific approaches are needed for prevention, early detection, rapid response, management and control of alien species, and identification of restoration measures. Advanced techniques, including environmental DNA (eDNA) can help scale up efforts to better understand the diversity and distribution of species. Raising public awareness through education and research, social media and citizen science-based approaches are also essential. The researchers note that it is important to also strengthen the invasive species database through coordinated action between different sectors.

“We are really missing the actual impacts of these species on native biodiversity, so we have plans to work on evidence-based impact studies on invasive fish species in the southern Western Ghats. We also plan to submit reports based on this study to the state government taking necessary action in this matter, ”adds Smrithy Raj.

The team is also conducting studies on models that predict the impact of climate change on the future spread of species and working on policy guidance to control their spread.



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