A recent report published in the journal BioScience highlights that overfishing of freshwater fish is threatening biodiversity in rivers and lakes worldwide. This issue significantly impacts food supply and employment in developing countries. 
“This is a real threat” – Kirk Winemiller, a fisheries researcher at Texas Agricultural Experiment Station, stated – “Currently, freshwater fish species face more risks than saltwater fish“.
The report mentions several rivers and lakes, including the Mekong River, which is home to the Mekong giant catfish – the largest freshwater fish in the world (weighing up to 300 kg and measuring 2.7 m in length) – and many other large fish species that are at risk of extinction.
Other endangered fish species include the Murray cod in the Murray River basin (Australia) and the sturgeon in the Great Lakes (North America).
Global fish harvesting in rivers and lakes has quadrupled since 1950, with an annual catch of approximately 8.7 million tons of freshwater fish, two-thirds of which is caught in Asia.
In the Mekong River basin alone, the average annual fish consumption is 56 kg per person. Among the heavily fished species are some of the largest and rarest fish in the world, such as the Mekong giant catfish, long-tail catfish, and thorny catfish.
Zeb Hogan, a fish researcher at the University of Wisconsin-Madison (USA) and a leading researcher for the National Geographic Society, noted that in recent years, the chances of catching the Mekong giant catfish have significantly decreased, from 60 fish in 1995 to just 4 fish in 2005. He expressed concern that this species may soon become a legend.
The report also indicates that humans have employed various methods to catch fish of different sizes, starting with the largest and gradually moving to smaller species, leading to the depletion of fish stocks.
“Large fish are essential for reproduction – David Allan, a Professor of Conservation Biology at the University of Michigan and one of the report’s authors, stated – Reproductive ability increases with fish size, thus larger females are particularly important for the species’ survival“.
As larger fish become increasingly rare, smaller fish species “rise to prominence“. The Queme River in Benin, West Africa, has witnessed large predatory fish like Nile perch being replaced by smaller species such as cichlids and catfish.
According to researchers, depleting fish stocks could have severe implications for human health, especially in developing countries.
For instance, the rising incidence of schistosomiasis in Africa is linked to the decline of fish species that feed on the snails that carry the disease. Moreover, for tens of millions of impoverished residents in Asia and Africa, freshwater fish are a vital source of livelihood.
Therefore, conserving this resource is crucial for the survival of the poor.
