Alien catfish invasion raises alarm over Pakistan’s freshwater ecosystems

An invasive fish species has begun spreading through waterways in Sindh and Lower Punjab, prompting warnings from conservationists about serious risks to biodiversity and the fisheries economy.

WWF-Pakistan said an unusual fish was brought to Karachi Fish Harbour on January 4 after being caught in a dhand near Sukkur. The species was later identified as the Amazon sailfin catfish, an exotic fish not native to Pakistan’s waters.

According to the organisation, the fish has a thick, armoured body covered with bony plates and is believed to have been accidentally introduced into natural water bodies. It has now established itself in parts of Sindh and Lower Punjab, making eradication or effective control virtually impossible.

Native to Latin America, the Amazon sailfin catfish is widely sold around the world as an aquarium fish and is known for its ability to rapidly colonise new environments. WWF-Pakistan warned that the species is among at least 26 invasive fish that have entered Pakistan either deliberately or unintentionally and are now harming aquatic biodiversity.

The organisation said invasive fish disrupt ecosystems by competing with native species for food and space, preying on them, spreading diseases and altering habitats. Such changes can lead to biodiversity loss, damage to fisheries, increased water turbidity and, in severe cases, the collapse of entire ecosystems.

Pakistan has a long history of introducing exotic fish species, often to boost aquaculture or control weeds, without fully assessing environmental consequences. Brown trout and rainbow trout were first introduced in Khyber Pakhtunkhwa in 1928, followed by species such as Mozambique tilapia, common carp, goldfish and grass carp in the 1960s. Many of these species later became invasive and harmed local fish populations.

Further introductions in the 1980s, including silver carp, bighead carp and Nile tilapia, also spread into natural ecosystems. While these species were intended to increase fish production, their impact on native fauna and flora was largely overlooked.

WWF-Pakistan noted that tilapia introductions in the 1960s had particularly devastating effects on indigenous fish in warm-water regions. Fish production in Manchar and Keenjhar lakes fell sharply due to the rapid breeding and growth of tilapia, causing serious economic hardship for local fishing communities.

Over the past three decades, several catfish species, including North African catfish, walking catfish and channel catfish, have also been introduced and are now spreading widely, further threatening native fish stocks.

The organisation added that species such as the Amazon sailfin catfish, guppies and mollies have entered natural waters through improper handling and disposal linked to the aquarium trade. These fish, it said, are now wreaking havoc in rivers, lakes and streams, particularly near urban areas, underscoring the urgent need for stronger controls and public awareness to protect Pakistan’s fragile aquatic ecosystems.