Invasive ‘alien’ fish spreads in Pakistani waters, threatens biodiversity

KARACHI: The WWF-Pakistan has cautioned that an invasive fish species has been detected in water bodies across Sindh and Lower Punjab, warning that its spread poses a serious threat to aquatic biodiversity and the fisheries economy, Geo TV reported.

In a statement released on January 4, the environmental organisation said an “unusual fish” was brought to Karachi Fish Harbour from a dhand near Sukkur. The species was initially described as “alien” because it could not be identified by those who encountered it.

The fish was later confirmed to be an Amazon sailfin catfish. According to WWF-Pakistan, the species has a thick, armoured body covered with bony plates and is not native to Pakistan. It was accidentally introduced into natural water bodies and has now established itself in Sindh and Lower Punjab, Geo TV reported.

“The Amazon sailfin catfish is native to Latin America and is popular around the world as an aquarium fish. This species is known to be a highly successful invader, and since this species is now widely spread in Pakistan, its eradication and control are impossible,” the statement said.

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WWF-Pakistan noted that the Amazon sailfin catfish is among 26 invasive fish species that have been introduced into Pakistan either accidentally or deliberately. These species, the organisation said, have become invasive, are harming aquatic biodiversity and threatening the fragile balance of local ecosystems.

“Invasive fish species are known to severely disrupt aquatic ecosystems by outcompeting natives for food and space, preying on them, introducing diseases, and altering habitats, leading to biodiversity loss, economic damage to fisheries, and even ecosystem collapse, with impacts ranging from increased water turbidity to native fish extinctions and significant losses in commercial fishing revenue,” WWF-Pakistan said.

The organisation added that the spread of invasive species is considered a major threat to sensitive aquatic ecosystems in Pakistan, including rivers, streams and lakes, Geo TV reported.

Providing historical context, WWF-Pakistan said brown trout and rainbow trout were the first exotic fish species introduced in Pakistan, brought to Khyber Pakhtunkhwa in 1928. In the 1960s, several other exotic species — including Mozambique tilapia, common carp, goldfish and grass carp — were introduced to boost fish production and control aquatic weeds, but all later became invasive and adversely affected native fish populations.

During the 1980s, additional species such as silver carp, bighead carp, Nile tilapia and blue tilapia were introduced, while grass carp was reintroduced to enhance aquaculture. All these species also established themselves in natural ecosystems, impacting local flora and fauna, as environmental consequences were not adequately considered at the time, Geo TV reported.

“There is no disagreement that these introductions, including those of trouts, have affected aquatic biodiversity and the natural ecosystem,” the statement said.

Referring to tilapia, the organisation said its introduction in the 1960s had devastating consequences for indigenous fish species, leading to partial or complete eradication of commercial fish from key water bodies in warm-water regions.

“Fish production from Manchar and Keejhar Lakes was drastically reduced due to prolific breeding and growth of tilapias, having a serious socio-economic impact on the fishermen of the area.”

WWF-Pakistan further said that over the past three decades, several catfish species — including North African catfish, walking catfish, magur catfish, blunt-toothed African catfish and channel catfish — have been introduced and are now spreading rapidly, causing serious harm to local fish fauna.

In addition to intentional introductions for aquaculture, the organisation said species such as the Amazon sailfin catfish, guppies and mollies have entered natural ecosystems due to poor regulation and handling in the aquarium trade, as per Geo TV.

“These fish are creating havoc in natural water bodies, especially around cities and towns, throughout Pakistan. WWF-Pakistan is cognizant of the ill effects of the introduction of exotic and known invasive species in the country.” (ANI)