ALAPPUZHA: The increasing presence of invasive fish species in the Vembanad lake ecosystem is raising serious concerns among the fishing community and environmental experts.
A recent study conducted by the Kerala University of Fisheries and Ocean Studies (KUFOS) and the Ashoka Trust for Research in Ecology and the Environment (ATREE) has revealed a significant decline in native fish species in the lake over the past two decades, while the population of exotic fish species continues to rise.
According to M K Sajeevan, head of the department of fisheries resource management at KUFOS, several invasive species — including redbelly (commonly known as piranha), sucker fish, gourami, carp, tilapia, and African catfish (African muzhi) — have been found in various parts of the lake as well as in nearby fish markets and landing centres over the years.
“The presence of sucker fish, a species native to South America, is a major ecological concern. It has adapted rapidly to local habitats and is now widely distributed in the freshwater-dominated southern regions of Vembanad lake,” Sajeevan said.
He warned that these invasive species feed on native fish and their eggs, threatening their survival. Moreover, many of these species can thrive in freshwater, brackish water, and even polluted environments, giving them a significant survival advantage.
“If their spread continues unchecked, their population could multiply rapidly over the next one or two decades, leading to the disappearance of many native fish species from the lake,” he added.
Maneeja Murali, senior programme officer at ATREE’s Community Environmental Resource Centre, said the breeding and spread of invasive species pose a serious threat to the lake’s ecological balance.
ATREE has been conducting annual fish counts in Vembanad lake since 2008 with the support of fishermen’s organisations, NGOs, and research institutions. “During the 1970s and 1980s, Vembanad lake was home to around 200 to 300 species of finfish and shellfish.
However, this year’s survey documented only 63 species of finfish and 10 species of shellfish. While shellfish availability was better compared to previous years, the decline in fish diversity is alarming,” Maneeja said.
Experts attribute the spread of exotic fish species largely to the expansion of aquaculture and cage farming in rivers and lakes. Many farmers have established fish farms near water bodies, and during periods of heavy rainfall and flooding, fish escape into nearby rivers and eventually reach the lake.
The floods of 2018 accelerated this process, as numerous fish ponds overflowed and cage farms were damaged, releasing large numbers of exotic species into the natural ecosystem. The study also found a sharp decline in several native species, including the Kuttanad pearl spot (karimeen), prawns (konchu), snakehead murrel (varal), kari, and many other indigenous fish varieties that once thrived in Vembanad lake.
Lake Inhabitants
Exotic species
Clarias (African muzhi)
Tilapia (Silopi)
Carp
Suckermouth catfish (sucker)
Redbelly (piranha)
Gourami
Native species
Sea bass (kalanji)
Snapper (chemballi)
Gerres (pranjil)
Halfbeak (kolan)
Channa (varal)
Giant freshwater prawn (attukonchu)
Scatophagus (nachu karimeen)
Pearl spot (karimeen)