Unveiling the invasion: Alien fishes spotted in Manipur's rivers

Dr Rameshori Yumnam *

The recent flooding in Manipur has left residents bewildered as they grapple with the aftermath of this unusual event. Unlike typical flooding patterns observed in the region, this deluge has taken on a particularly strange nature, prompting questions and concerns among locals and authorities alike.

Manipur, nestled in the North Eastern part of India, is no stranger to the monsoon rains that frequently inundate the region. However, the recent flooding has surpassed previous occurrences in both intensity arid unpredictability. Rivers swollen beyond their usual bounds spilled over into city, towns and villages, wreaking havoc on infrastructure and livelihoods.

The implications of this strange flooding event are far-reaching. Beyond the immediate damage to infrastructure and agriculture, there are concerns about the long-term impact on the region's ecosystems and biodiversity. Rivers and water bodies are crucial habitats for a diverse array of flora and fauna, and the disruption caused by flooding could have lasting consequences for these delicate ecosystems.

What makes this flooding even more peculiar is a curious phenomenon that has been unfolding-the emergence of alien fishes during this devastating floods that wreaked catastrophe across the State, in the serene waters of Manipur's rivers. These aquatic interlopers, not native to the region, have been making their presence felt, raising questions and concerns among scientists and local communities alike.

The rivers of Manipur, known for their ecological richness and biodiversity, harbouring more than 300 fish species, have recently become home to several non-native fish species. The appearance of fish species like the Suckermouth catfish also known as Amazon Sailfin catfish (Hypostomus plecostomus) and Alligator gar fish (Atractosteus spatula) was peculiar, despite the presence of other alien species in Manipur previously.

Let's also remember the appearance of the Suckermouth catfish two years ago on April 22, 2020, at Waishel Bishnupur, as documented in the Hindustan Times. This emergence of alien fishes has sparked debates and discussions regarding its implications on the local ecosystem and the livelihoods dependent on these water bodies.

The alligator gar, an ancient fish, originating from North America, is classified as an alien fish species, indicating its presence outside its natural habitat. Belonging to the Lepisosteidae family, gars have existed for over 150 million years since the late Jurassic Period alongside dinosaurs.

The alligator gar, the largest member of the gar family, can exceed 240 centimeters in length and weigh over 130 kilograms with a lifespan of over 100 years. With rapid growth, they can reach lengths of over 50 centimeters within their first year under favourable conditions.

While harmless to humans, they possess a voracious appetite and will consume any prey they can swallow whole, lacking the ability to bite off pieces of flesh. If alligator gars were to establish a substantial population capable of successful reproduction and the survival of young-of-year fish (under a year old), they could potentially disrupt the ecosystem of the lake where they are not native. (Comments by Solomon R. David, an aquatic ecologist and Assistant Professor of Biological Sciences at the Nicholls State University in Louisiana, USA, as documented in Mongabay, June 5, 2023).

Suckermouth catfish is a tropical freshwater fish categorized under the armored catfish family (Lorica-riidae). It earns its name from the rows of armor-like scutes covering the upper parts of its head and body,’ while the lower surface of the head and abdomen features naked, soft skin. They exhibit remarkable resilience, with their armored bodies enabling them to thrive even in heavily polluted waters. These fish are sold when they are young and small in aquarium trade, but in the wild, they can grow to be a maximum size of 50 centimetres.

In fact, freshwater aquaculture and ornamental fishery sector heavily relies on alien or non-native fish species, which can pose a problem when they escape in the wild. Numerous fish varieties, such as tilapia (Oreochromis mossambicus), African sharptooth catfish (Clarius gariepinus), common carp (Cyprinus carpio) etc., are cultivated on a worldwide scale.

Interestingly, tilapia production surpasses that in their native African habitat within their invasive territories. Non-native freshwater fish have the potential to escape into water systems, particularly in facilities lacking barriers to prevent their dispersal. The introduction and proliferation of alien fish when they become invasive will disrupt the stability of the natural ecosystem in open water bodies.

Such replacement and expansion of invasive fish species will not only result in a loss of aquatic biodiversity, but will also cause the extinction of indigenous fish species in the ecosystem. As per International Union of Conservation of Nature (IUCN), Invasive Alien Species (IAS) are species that are introduced, accidentally or intentionally, outside of their natural geographic range and becomes problematic gradually.

And for a species to become invasive, it must successfully out-compete native organisms for food and habitat, spread through its new environment, increases its population and harm ecosystems in its introduced range, states the Convention on Biological Diversity (CBD).

Researchers are scrambling to understand the factors contributing to this phenomenon. One prevailing theory suggests that human activities, such as introduction through aquaculture, ornamental fish trade or accidental release of pet fishes, may be responsible for the spread of these alien species.

Another possibility is the changing climate patterns, which might be creating favourable conditions for these fishes to thrive in new habitats. The implications of the presence of alien fishes are profound. They could potentially outcompete native species for resources, disrupt the delicate balance of the ecosystem, and even pose a threat to the traditional fishing practices of local communities. Moreover, there are concerns about the spread of diseases and parasites associated with these alien species, further complicating the situation.

There are still deficiencies in the Nationwide evaluation of how Invasive Alien Species (IAS) affects the economy, biodiversity, and food security. It's crucial to enhance our comprehension of the factors leading to alien species becoming invasive, their introductory pathways into natural ecosystems, and to enforce environmental laws strictly while raising awareness among local communities.

Therefore, efforts need to be taken underway to address this emerging challenge. Scientists should take up extensive studies to assess the impact of alien fishes on the local environment and biodiversity. Conservationists should advocate for stricter regulations on the trade and release of non-native species to prevent further proliferation.

Additionally, community awareness programs should be conducted to educate local residents about the risks posed by these alien invaders and the importance of preserving native biodiversity.

The emergence of alien fishes in Manipur's rivers serves as a stark reminder of the interconnectedness of ecosystems and the fragility of our natural world. It underscores the need for proactive measures to protect and preserve the rich biodiversity of these water bodies for future generations.

Only through concerted efforts and collective action can we hope to mitigate the threats posed by invasive species and ensure the sustainability of our precious aquatic ecosystems.