African Sharptooth Catfish: A Hardy Invader in China's Waterways

The recent discovery of African sharptooth catfish in Nanning’s sewage system, located in Guangxi Province, China, has sparked public interest and scientific concern. This unexpected finding sheds light on the extraordinary adaptability of this invasive species and its potential implications for urban infrastructure and ecosystem health.

The African sharptooth catfish possesses several remarkable survival characteristics that make it uniquely adapted to harsh environments. These fish can survive in water with pH levels ranging from 5 to 9, demonstrating exceptional tolerance to both acidic and alkaline conditions. Their most distinctive feature is a specialized dendritic breathing organ that allows them to breathe air directly, enabling survival in oxygen-poor environments and even brief periods out of water.

Perhaps most concerning is the species' ability to bioaccumulate harmful substances. Research has shown these fish can concentrate heavy metals such as lead, mercury, copper, iron, manganese, zinc, and cadmium in their muscle tissue, intestines, and gills. This bioaccumulation poses potential health risks if the fish enter the food supply, particularly when sourced from polluted environments.

The species' presence in China marks a significant shift from its original introduction in 1981 from Egypt and Central Africa. While it was initially bred for aquaculture, its commercial cultivation in China has declined due to poor meat quality and food safety concerns. However, the fish has established itself in natural waterways, particularly in southern China’s water systems.

In Guangdong Province, for example, the African sharptooth catfish has become one of the most common invasive species, contributing to the decline of native fish populations. Historical records show that of Guangdong’s original 351 native fish species, only 223 remain after 2010, with 23 invasive species, including the African sharptooth catfish, now present in local waters.

The environmental impact extends beyond simple competition with native species. These catfish can thrive in heavily polluted waters where few other species survive. Studies have shown they can endure water containing up to 8.2% sewage concentration, though their growth rate and survival decrease as pollution levels rise.

This adaptability presents a complex challenge for environmental management. While the species' ability to survive in polluted environments might seem beneficial for wastewater treatment, their presence in urban infrastructure and natural waterways poses risks to both ecosystem balance and public health. The situation in Nanning serves as a warning about the unintended consequences of introducing non-native species and the challenges of managing their spread in urban environments.

The presence of these fish in sewage systems also raises questions about their potential entry into natural waterways and the food supply chain. Given their ability to bioaccumulate toxins, there are legitimate concerns about public health risks if these fish are harvested from polluted environments for human consumption.