Aquaculture, the practice of farming fish and other aquatic organisms, has become the world's fastest-growing food production system. The sharpest growth in aquaculture is occurring in Africa, where average annual growth rates have exceeded 10% in recent years, indicating a remarkable expansion. Over the past decade, Lake Victoria has undergone significant transformation from a small-scale enterprise to a vast and diverse commercial industry, with cage aquaculture playing a pivotal role.
This freshwater lake, ranking second globally by surface area, serves as the epicenter for rapid expansion of cage aquaculture. These structures are crafted from nets in frames, predominantly stocked with Nile tilapia, which has adapted well to this farming method.
The number of fish in a cage farm varies widely, ranging from tens to hundreds of thousands. Cage aquaculture now accounts for about 25 percent of Kenya's total fish production, while supporting the livelihoods and nutrition needs of over 40 million people in the lake's basin. We are environmental scientists who investigate biological threats to public health. Through our research, we have identified two interconnected challenges that this industry faces: large-scale fish deaths, also known as fish kills; and resistance to drugs used to treat diseased fish.
These mass die-offs involve the rapid death of hundreds of thousands or even millions of fish within a few days. Many farmers who encounter dead fish in their cages simply discard them into the lake, where they can easily wash up against another cage and transmit disease.
Despite the widespread use of antimicrobials – drugs like antibiotics – to manage and treat infectious diseases, antimicrobial resistance is a growing concern. Misuse of these drugs has led to the emergence of resistant bacteria, rendering treatments ineffective. Our study, conducted in Kenya, aimed to systematically examine both the causes of mass fish deaths and the spread of antimicrobial resistance in Lake Victoria's cage aquaculture industry. We found that fish deaths in this tilapia industry are likely driven by water quality problems, including low oxygen levels, pollution, and harmful algal blooms.
These issues can lead to the release of toxins and rapid drops in dissolved oxygen levels, creating an environment conducive to infectious bacteria. To address these challenges, we suggest:
* Establishing stronger disease reporting systems to enable prompt responses from industry authorities; * Implementing more effective management strategies to mitigate water quality problems; * Promoting responsible use of antimicrobials and developing alternative treatments for resistant diseases.
