While the aquaculture scene in the State is flourishing, fish species introduced for the purpose may pose a serious threat to indigenous biodiversity. Fish escaping from enclosures to open systems, mainly due to damaged netting or extreme climatic events like floods, often invade the habitat of native species, causing a dip in their population.
According to experts, many exotic species were released to Kerala waterbodies during the floods of 2018 and their numbers must have soared over the years. Farmed for their impressive growth rate, these fish can alter the aquatic ecosystem by competing with the native species and displacing them. Post-flood field surveys carried out by Kerala State Biodiversity Board had revealed the presence of alien species in the State’s major river systems and associated backwaters. It included high-risk species like Arapaima (Arapaima gigas) and Alligator gar (Atractosteus spatula) along with some aquarium varieties that are not permitted to be imported to the country.
A variety of anabas is now very popular among aquaculturists and inland fishers complain that the extensive cultivation is affecting the native stock. “It’s not the local variety as the authorities claim and they are changing our fishery pattern. They are also invading our wetlands depleting the stock of species like snake head and pearl spot,” says Gopi, a fisher from Alappuzha.
Carnivorous species
According to A. Biju Kumar, Professor and Head, Department of Aquatic Biology and Fisheries, University of Kerala, it’s a carnivorous species and its presence will have an impact on the indigenous fish. “It will also become a major competition for pearl spot by taking over its habitat. When cultivating such species, extra care should be taken to keep them confined. But at present we have no monitoring mechanism to ensure this,” he adds.
Though banned, species like African catfish is cultivated in many places since it’s very easy to farm them. The infestation of sucker catfish, an ornamental species from South America, is another threat to Kerala waterbodies as they easily outcompete endemic fish. “You will find a lot of large sucker catfish in the filthy Amayizhanchan canal in Thiruvananthapuram. It can survive in any polluted waterbody with minimal oxygen content,” says a top official with the Fisheries Department.
Norms not followed
Though there is no great threat as of now, GIFT tilapia, and Nile tilapia can compete with local species for feed and breeding space. “There are some strict biosecurity measures to farm tilapia. They need proper enclosure and bird net to prevent any kind of transport into our waterbodies. Despite knowing it’s really hard to control aquatic exotics, we hardly follow these guidelines,” says the official.
‘Not a good sign’
The widening gap between capture fisheries and consumption had prompted the authorities to promote large-scale aquaculture in Kerala. In cage culture the net pens often get damaged and some fish escape to the surrounding environment while heavy rains and subsequent floods pose another challenge. “Most of the banned aquatic species reach India illegally. Finding a fish endemic to the Amazon basin in our waterbodies is not a good sign and we need more research and regulatory measures to tackle the threat,” adds the official.
