Experts warn cage fish farming is a “disaster in waiting” for Lake Victoria

A new scientific review has raised serious alarms about the environmental consequences of cage fish farming in Lake Victoria, warning that the practice is negatively impacting native fish stocks and could lead to a long-term ecological disaster.

The review, titled “Environmental impacts of cage fish farming: A review,” was authored by Barirega Akankwasah, the executive director of the National Environment Management Authority (NEMA), and six other experts.

Published in the International Journal of Fisheries and Aquatic Studies, the paper highlights a number of environmental challenges posed by the open-system aquaculture, including:

Eutrophication: The discharge of waste from uneaten fish feed and faecal matter, rich in nitrogen and phosphorus, leads to a nutrient overload in the water. This causes excessive algae growth, which can deplete dissolved oxygen and create toxic conditions for fish.

Disease transmission: The open system allows for the easy exchange of diseases and pathogens between farmed fish and native fish populations.

Alterations in aquatic biota: The waste products can change the composition of aquatic life, including the decline of native species.

Degraded water quality: The buildup of ammonia and other byproducts is a significant threat.

A separate study by Kenyan researchers found ammonia levels around cages ranging from 0.14 to 0.2 mg/L, noting that even low concentrations can be toxic to fish.

These findings echo concerns raised in a study published less than two months ago, which specifically highlighted the ecological and genetic threats posed by Nile Tilapia cage aquaculture.

That study warned that escaped farmed fish could interbreed with native species, leading to a loss of genetic diversity and a disruption of the ecosystem. The researchers emphasize that while cage farming offers economic benefits, with a single 8-12 m³ cage able to produce a ton of fish in eight months, these gains could come at a significant cost to the long-term sustainability of Lake Victoria.

They point to the mass fish deaths that occurred in January 2021 at various landing sites in Wakiso as a potential consequence of such environmental degradation. To prevent a disaster, the NEMA-led review recommends that future developments in the aquaculture sector must integrate advanced waste management and environmental monitoring systems.

A separate study by researchers from the Kenya Marine and Fisheries Research Institute also stated that a proper policy framework for lake-zonation is needed to ensure that all stakeholders can use the lake without harming the environment. Without proper guidelines, the report concludes, cage farming is likely to be an environmental disaster.