After the devastating 2018 Kerala floods, several photographs and videos of ‘weird’ fish caught by local fishers made headlines and were widely shared on social media platforms. This caught the attention of Smrithy Raj, a doctoral researcher, studying invasive alien fishes at the University of Kerala. Raj is part of the team that studied freshwater ecosystems across Kerala from 2016 to document the presence of alien aquatic species.
Their findings, recently published in Aquatic Ecosystem Health & Management, states that Kerala’s waters are home to 28 alien fish species and four alien aquatic weeds or macrophytes.
“Alien species are introduced in India mainly for the purpose of diversification of species in aquaculture, aquarium trade, biocontrol of mosquitoes and game fishing. These fishes, when they escape into the natural water bodies, tend to threaten the native biodiversity and disrupt other ecosystem services,” explains Smrithy Raj.
Just out in Aquatic Ecosystem: Health and Management!
the distribution of 28 species of #freshwater #alienfish in the southern part of the #WesternGhats https://t.co/ZHXajJdPJp@IUCN_ISSG @FW_Conservation @Shoal_Org @AFL_org @wildlifeinwater @fwlifeorg pic.twitter.com/iVxjkXA52E
— Rajeev Raghavan (@LabRajeev) September 21, 2021
The surveys were conducted in 44 rivers and 53 reservoirs of the state. The most common invasive species recorded were Oreochromis mossambicus and Cyprinus carpio.
Also known as Mozambique tilapia, O.mossambicus is a native of Africa and can grow to about 39cm and weigh a little over a kilogram. It was found in 44 rivers, 25 reservoirs, and two freshwater lakes of Kerala.
Cyprinus carpio, or the common carp, has been cultured for about 2500 years and is a popular angling and ornamental fish. According to the International Union for Conservation of Nature, “C. carpio is the third most frequently introduced species worldwide and on every continent where it has been introduced it has reduced water quality and degraded aquatic habitats.”
Route of entry
The team noted that of the 32 alien species, 15 were introduced through aquarium hobby and trade, six species were introduced for promoting aquaculture, three for mosquito control, and three species for either aquarium keeping or promotion of aquaculture.
“The rainbow trout, Oncorhynchus mykiss, was introduced during the colonial period to promote sport fishing, the only species introduced for this purpose,” adds the paper.
The maximum number of exotic fish species was recorded from Chalakudy river, which harboured 11 exotic fish species of which eight species were recorded after the flood, which includes the rare mega fish like Arapaima gigas.
Another paper published by the team in April noted that: “high magnitude flooding events in August 2018 and 2019 resulted in the escape of at least ten alien fish species that were recorded for the first time, from the natural waters of the Western Ghats.”
One of the authors of the paper Rajeev Raghavan from the Kerala University of Fisheries and Ocean Studies explains that several illegal farming systems could have facilitated the escape of alien species. “With increasing extreme climate events, we may see the spread of more alien or non-native species in the state. There needs to be a check on illegal aquaculture in Kerala which is now functioning for aquarium purposes.”
BREAKING NEWS: One-third of freshwater fish face extinction
Undervalued and under threat, we must act now to save them reveals major report on world’s #ForgottenFishes
— IUCN Water Programme (@IUCN_Water) February 23, 2021
He adds that there is an urgent need to study the route of entry of these alien species and maybe use bio-secure fences near hatcheries that raise non-native species. When asked if there is a method to remove these invasive fish from the water bodies, he said: “Recently, the Periyar Tiger Reserve launched a drive to eradicate African catfish in Periyar Lake. Officials noted that over 450 kg of African catfish was fished out in three days. Maybe we can try this initiative on a larger scale but it would be impossible to completely fish them out.”
The team documented four macrophytes or aquatic weeds in Kerala’s water bodies – Salvinia molesta, Pistia stratiotes, Eichhornia crassipes and Cabomba furcata. The first three plants were introduced as garden plants or for promotion of research. The team writes that their entry into natural systems is believed to be accidental.
Cabomba furcata might have entered natural water bodies either from home aquaria or from ponds which were used for rearing aquarium plants.
“A few organisations are now trying to make value-added products using these invasive weeds. They can be used as manure, wet material for mushroom farming, and for the production of a host of value-added products. If we can find a commercial purpose for these weeds maybe we can eradicate them slowly from our waters,” says Appukuttannair Biju Kumar, from the Department of Aquatic Biology & Fisheries at the University of Kerala and corresponding author of the work.
How to manage aquatic invasive species?
The team notes that science-based 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 intensify efforts to better understand species diversity and distribution. 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 database of invasive species through coordinated action between various sectors.
“We really lack the actual impacts of these species on the native biodiversity so we have planned to work on evidence-based impact studies on the invasive fish species in the southern Western Ghats. We also plan to submit reports based on the present study to the state government in taking necessary steps in this matter,” adds Smrithy Raj.
The team is also carrying out studies on models that predict the impact of climate change on the future spread of species and working on policy guidelines to control their spread.