Checking spread of invasive alien fish as India faces climate extremes

Seedlings of Pterygoplichthys sp. Photo by Ajmal Hussan.

Seedlings of Pterygoplichthys sp. Photo by Ajmal Hussan.

  • Extreme climate events may aid the spread of alien species in biodiversity hotspots, such as the 2018 and 2019 flood-driven release of alien species like the alligator gar from illegal aquaculture farms in Kerala to its natural water bodies.
  • Compliance and enforcement of existing environment protection laws in India can check the spread of alien species. An exclusive policy on invasive alien species and overseeing agency may give more teeth to management of such species.
  • Countrywide assessment of impacts of IAS on the economy, biodiversity and food security are needed to understand the nuances of the issue.

Degrading quality of natural water bodies and rivers, coupled with climate change impacts, could set the stage for alien (invasive) species to take root, multiply and alter aquatic flora and fauna in biodiversity hotspots, warned scientists, documenting alien fishes in the Western Ghats.

In a paper, scientists at the University of Kerala reiterated concern over the expansion of alien, or non-native species in biodiversity hotspots triggered by extreme climate events, such as the flood-driven release of alien species from illegal aquaculture in Kerala, an Indian state on the southwest tip of India that sees the onset of the southwest monsoon as it sweeps into India in June. 

“In India, there are no specific policies to address the issue of invasive alien species (IAS), though it is part of several existing biodiversity legislation and regulations,” explained Smrithy Raj, lead author of the paper and a PhD student working on alien species at the university.

The National Biodiversity Strategy and Action Plan published in 2014 has several suggestions for the regulation of the introduction of invasive alien species and their management but none of the suggestions is put into practice; besides, there is no national mechanism or an institutional mechanism to foresee and enforce this, said Raj. The researchers call for monitoring tools such as environmental DNA to keep tabs on these hardy non-native species in Indian waters.

Gaps also remain in the countrywide assessment of impacts of IAS on the economy, biodiversity and food security. There is a need to better understand the factors that trigger alien species to become invasives and pathways of introduction to natural ecosystems, and for strict enforcement of environmental laws and awareness among local communities, experts said.

Invasive alien species are species that are introduced, accidentally or intentionally, outside of their natural geographic range and that become problematic, states the International Union of Conservation of Nature. For a species to become invasive, it must successfully out-compete native organisms for food and habitat, spread through its new environment, increase its population and harm ecosystems in its introduced range, states the Convention on Biological Diversity (CBD). 

High magnitude floods in August 2018 and 2019 resulted in the escape of at least ten alien fish species that were recorded for the first time in the water bodies and rivers snaking through the Western Ghats following the floods. Illegal farming systems, aqua-tourism destinations and amusement parks, and reservoirs facilitated the escape of alien species.

A man displays an alligator gar caught from a river in Kerala. The fish can measure up to three metres in length and could put the native fish species at risk. Photo from Smrithy Raj.
A man displays an alligator gar caught from a river in Kerala. The fish can measure up to three metres in length and could put the native fish species at risk. Photo from Smrithy Raj.

Among the species that popped up in water bodies were megafishes such as the arapaima (Arapaima gigas), also called ‘river monster’, that normally live in the Amazon lowlands waters and the torpedo-shaped alligator gar (Atractosteus spatula), one of the largest freshwater fishes in North America. They were not listed in the species allowed to be imported to the country.

The future management of IAS should consider and integrate climate change as a major factor, adds Bijukumar, another co-author of the study, sharing that “we need to come up with strong policies on importing dangerous (large-growing carnivorous) fishes such as arapaima and alligator gar into the country.” 

Bijukumar, professor and head of the university’s Department of Aquatic Biology and Fisheries adds that many existing farming and rearing systems have very little biosecurity related infrastructure to prevent the escape of captive fish into adjoining natural ecosystems during floods and ECEs. The issuance of specific guidelines by state fisheries departments and other environment and biodiversity agencies is needed “to make sure that such fish are not being held in ponds or other farming and rearing systems adjacent to rivers and natural water bodies.”

Most of the alien species that enter India are principally for ornamental trade. West Bengal is the largest ornamental fish producer in India, followed by Tamil Nadu; the trend is catching up in Kerala, fanned by a swelling rank of aquarists, many of who are not aware of the potential pitfalls of dumping exotics in water bodies after they exceed the length of their tanks.

Identify invasive species

A list of IAS compiled by the Centre for Biodiversity Policy and Law (CEBPOL), National Biodiversity Authority (NBA) and updated in 2018 identifies 169 species as invasives with the break up identifying aquatic ecosystems harbouring the highest number of intruders at 55 species. The Zoological Survey of India under India’s environment ministry has listed 157 animal species including 99 marine species as invasive and 19 species of freshwater fishes.

S. Sandilyan, fellow at CEBPOL, who led the IAS list compilation, suggested a mapping exercise of aquaculture farms in flood-prone areas so that aquaculturists can be advised to prohibit the culture or stocking of alien varieties in the flood/monsoon season as a stop-gap measure. For example, in the low-lying area of Kolathur in Chennai, a hub of ornamental fish trade, monsoon floods, like the one in December 2015, wash away the breeding stock and adult alien fishes into water bodies.

Researchers note that many local community members, residing near beels (flood-plain wetlands) in Assam, grow the carnivorous African catfish (Clarias gariepinus) in their backyard drain or nalas, feeding them with household sewage and that it has a “great chance” to escape to the nearby beels during the flood or heavy rain. The Indian government banned the breeding of the species in 2000 but the practice still thrives in many parts of the country.

In Manipur, the recent reports of the emergence of Amazon sailfin catfish in water bodies have concerned experts. Ichthyologist Rameshori Yumnam based at the Manipur Unversity also attested to the accidental release of exotic fishes from aquaculture farms to rivers during floods. “Due to improper management of aquaculture farms these fishes leak out of farms into rivers during floods. For northeast India, we do not have a comprehensive list of IAS; due to lack of awareness often people are also not able to tell if a fish is indigenous or exotic,” Yumnam said.

African catfish and suckermouth catfishes (Pterygoplichthys species) are among those included in the list that was compiled by CEBPOL.

Traditional physical barrier in use at East Kolkata Wetland to minimise the intrusion of Pterygoplichthys in the pisciculture bheries (ponds) from sewage feeder channel. Photo by Ajmal Hussan.
A traditional physical barrier in use at East Kolkata Wetland to minimise the intrusion of Pterygoplichthys in the pisciculture bheries (ponds) from sewage feeder channel. Photo by Ajmal Hussan.

Ajmal Hussan, scientist at the ICAR-Central Institute of Freshwater Aquaculture at Kalyani in West Bengal, informed all four common species of this genus (Pterygoplichthys pardalis, P. multiradiatus, P. anisisti and P. disjunctivus) have been reported from inland water bodies of the country. 

“The suckermouth catfishes are highly resilient, have armoured bodies and thrive very well in polluted waters. While we have not yet studied the consequence of extreme climatic and environmental events like abnormally high temperatures, flooding etc. on its spread and establishment in natural water bodies in Bengal, what we have seen is that the nutrient load in water bodies (pollution) appears to speed up their proliferation,” Hussan told Mongabay-India. 

For the fisherfolk community, based in the East Kolkata Wetlands, considered as the world’s largest wastewater fed aquaculture system where city sewage feeds traditional practices of aquaculture and agriculture, the suckermouth catfish is of particular concern. So far, said Hussan, only P. disjunctivus and P. pardalis, and many intermediary forms (likely hybrids of these two species) have been reported in the wetlands, observed Hussan.

“We first came to know about the suckermouth catfish in the wetlands around 20 years ago. Since then they have expanded exponentially. They have a spiny exterior that injures the native fishes that we cultivate in our ponds and they modify the pond ecosystem so that other organisms cannot survive properly,” 53-year-old fisher Shyamal Mondal told Mongabay-India.

Sneaking their way through sewage feeder canals, the fish embraced the shelter and breeding refugia provided by water hyacinth, another invasive aquatic species that was introduced to India by the British in the 1890s.

Mondal says five years ago, the yield of fish per year from ponds in a bigha of fish pond area (0.13 hectares in Bengal) in the wetlands used to be 1200 kg but now it has retreated to 800 kg, attributing the decline largely to the invasives that use up space and compete with native fishes for resources in the aquacultures.

Mondal and his fellow farmers have been trying to innovate to control their populations but nothing seems to work. “We have tried dredging ponds, capturing the catfish and started afresh; but because they are in every pond, they seem to come back to the dredged ponds once we re-start cultivation. Because the wetlands are vast (12,500 hectares), you would have to dredge all the ponds simultaneously to manage their expanding populations,” he adds.

They are usually averse to consuming the fish; setting up bamboo fences and netting to stop their spread hasn’t borne fruits – the hardy fishes disrupt the barriers with their spiny bodies. They usually cull the catfishes when they come through in their bycatch. Even using them as ingredients for fish meal for animal feed hasn’t worked out yet.

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More breed exotic than native

It is also important to understand when to declare a species as invasive. “All aliens (species) are not invasive species, but all invasives are aliens. Most aliens are in a lag phase in India (adjusting to their environment); we have to examine what kind of environmental factors trigger them to be invasive; for example, climate change is a factor,” Sandilyan observed. Additionally, a population may be invasive in one Indian state but not in other states, which is why “we have to periodically revise and update the list of IAS.” 

There are learnings from other regions that put the significance of management of IAS into perspective. In England, the Salmon and Freshwater Fisheries Act of 1975 clearly states that the transport of native and non-native fishes within the political boundaries without proper procedure is illegal. Apart from established IAS, Norway also conducts ecological risk assessments of several species known as “door knockers“, which are alien species with the potential to establish in Norway.

Given the multifaceted nature of the problem, Sandilyan feels a shift in tone is inevitable, i.e. a new law or regulation on IAS management is crucial; but that would entail attention to a few focal points and having an implementing/monitoring agency are necessary. “One is strictly regulating ornamental species trade, both online and conventional. We have to educate pet owners to be more responsible. If you want to introduce a species in India we have to develop indigenous risk management tools/kits. We have to stop the introduction of alien aquaculture species and also plants,” he added. 

India’s share in the global ornamental fish trade (export) is less than one percent. The majority of fish breeders in India breed exotic fishes and very few breed indigenous fishes. Over 300 exotic species are believed to be integral to India’s ornamental fish trade.

Aquatic conservation biologist Rajeev Raghavan, the other co-author of the Western Ghats paper debunks the “myth” that aquaculture production can be augmented only with farming alien species.

“The use of many ‘harmless’ species in aquaculture can be justified as long as they remain in the culture system. In rivers, Ganges and Yamuna, exotic fishes like Cyprinus carpio and Nile tilapia support the local fishery as well. But in a holistic perspective, the indigenous species supported the livelihood of hundreds of fishers in the basin, and when these species declined, it currently supports a lesser number of fishers in the basins,” said Raghavan, based at the Kerala University of Fisheries and Ocean Studies (KUFOS).

Before their introduction, the economic benefits of exotic species have to be assessed comprehensively taking into account the ecosystem services provided by the indigenous species and their support to local fishery coupled with their role in the local food web (as predator and prey), he notes.

Indian aquaculturists are lured to breed exotic fishes because the Package of Practices (PoPs) for these fishes are well developed in the species’ home countries such as Vietnam; unlike those for breeding native freshwater fish in India.”We have strong PoPs for legalised exotic shrimps being grown in coastal and brackish water environment, and we need the same attention for native freshwater fishes,” said Jitendra Kumar Sundaray, head at Division of Fish Genetics and Biotechnology at ICAR-Central Institute of Freshwater Aquaculture, Bhubaneswar, Odisha.

“Secondly, we need a licensing system for aquarium traders, just as we have for diagnostic labs to regulate their activities and ensure vigilance,” added Sundaray who is working with collaborators on developing eDNA tools to monitor invasives in water.

Banner image: Seedlings of Pterygoplichthys sp. Photo by Ajmal Hussan.

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