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.
Although cage aquaculture does add to nutrient loading and localized water quality problems in Lake Victoria, a comprehensive evaluation reveals that it is not the main cause of eutrophication.
The primary contributors to this issue include sewage discharge, agricultural runoff, industrial pollution, and the proliferation of invasive plants such as water hyacinth. The ammonia levels originating from cages (ranging from 0.14 to 0.2 mg/L) are below the threshold for acute toxicity in tilapia, but they could still harm fish in conditions of low dissolved oxygen.
While there have been instances of fish mortality within cages, there is no definitive evidence linking any wild fish disease-outbreaks to aquaculture. The historical changes in the ecosystem, driven by species introductions and overfishing, have had a disproportionately larger impact than cage aquaculture, which is operating mostly within an already compromised environment.
Therefore, while cages do contribute to existing stressors, they are not the sole or most significant threat. It is crucial for policies to address ALL sources of nutrient input, enforce proper zoning regulations, and promote sustainable practices in order to avoid oversimplification, hyperbole and alarmism.
STOP PROMOTING THESE ECO-FASCITS. Apocalyptic Environmentalists.” While most people who describe themselves as environmentalists don’t consciously identify with apocalyptic environmentalism, key policies they support have their intellectual origins in this fringe.
Apocalyptic environmentalism, sees humanity and the environment as fundamentally at odds. Adherents are never far from advocating population reduction alongside demands for more government action.
For those with a doomsday outlook, signs of human life are a blight on nature. And if the government isn’t successful in preventing more human development around waterways like Lake Victoria, environmentalists argue, the consequences will be “dire,”
Based on my researh, I agree completely with Andrew Izaara.
Are the cage farmers sensitised on these dangers or they do as they wish, thinking profit and “to hell” with sustainability? Since NEMA knows these things, why not crack down on those damaging the lakes when it is still early?
At this point in time, one cannot rely on NEMA to address such issues. They (NEMA) seem to have their interests aligned with those of certain individuals for self aggrandizment
Like Andrew Izaara commented, Cage farming is not the main source of lake water contaminants, several contributors like industrial sewages and agricultural chemical runoff’s have contributed a lot.
Cage fish farming should be looked at as a great rescuer for our fish species in lakes from depletion by minimizing overfishing.
The government through its ministry of Agriculture, Animal husbandry and Fisheries should emphasize of sustainable practices among the fish farmers and this will help to keep our lakes more resourceful
It is important that we approach the debate on cage aquaculture with both science and perspective. While recent reviews have highlighted the risks of cage farming, we must also acknowledge the broader context of Lake Victoria’s ecological crisis.
Cage farmers are often singled out, yet studies consistently show that the largest nutrient inputs into the lake come from municipal sewage, agricultural runoff, industrial effluents, and invasive species like water hyacinth—not aquaculture. To focus blame disproportionately on cages risks ignoring the deeper systemic issues that continue to compromise the lake’s health.
Moreover, cage aquaculture plays a critical role in food security, poverty reduction, and youth employment, contributing alot to SDGs. With the natural fisheries of Lake Victoria long depleted by overfishing and the Nile perch introduction, aquaculture offers one of the few sustainable avenues for maintaining fish protein supplies to local communities. A single cage can yield a ton of fish in under a year—something traditional capture fisheries can no longer guarantee, while the population is demanding.
Therefore i wish to comment that ,the way forward is not to demonize cage farming but to regulate and innovate it. With proper lake zoning, stocking density limits, feed management, and investment in waste mitigation technologies, cage aquaculture can coexist with environmental sustainability. Indeed, many countries have demonstrated that aquaculture, when guided by policy and research, can be a net positive rather than a liability.
Therefore, the discussion should not be framed as “cages versus the lake,” but rather as “how do we balance livelihoods, nutrition, and environmental stewardship in an already stressed ecosystem?” Farmers deserve guidance, not condemnation, and Lake Victoria deserves holistic solutions that address all pollution sources, not selective ones.
I agree with you 100%. the constant attack on cage farming in Kenya is baffling, and we know in many cases politically sponsored. fish that come to Kenya from Uganda and China are all from cage farming.
Honestly speaking, aquaculture practice like any other livelihood activities has got to be managed properly. We cannot deny the fact that rearing caged-fish comes with negative ecological impacts and I agree with those challenges highlighted in the NEMA-led review.
See how scavenging birds are already perched to close proximity to the fish cage — could this create overdependency on caged-fish by fishing birds? Could this not constitute behavioral change?
I just think that, aquaculture initiatives — whether in oceans, lakes, and rivers — should not be developed in these traditional natural ecosystems. They should be developed in own systems by developing fish ponds whether land-based or in tanks. It’s the only guaranteed option to avoid uncertainties of aquaculture to the natural ecosystems.
behavioral change is a natural phenomenon in all living things. even building a new tarmac road in a place where there has been none will trigger a behavioral change in the ecosystem. Society changes with time based on the needs and possibilities of supplies to meet those needs.
currently, fish farming is the way to go in the lake region… let’s apply all the best practices as much as possible…there will always be negatives, but let’s ensure the benefits are more…from my observations, the benefits are already more…
While academic papers are presented and discussed in air conditioned conference halls, Lake Victoria is surreptitiously being privatised, by big multinational corporations whose principle motive is profit:
* Native species of tilapia and nile perch will decline, and only genetically modified varieties will survive inside the cages
* Traditional fishing industry operatives will be adversely affected: their craft and means of livelihoods shall be outlawed in favour of multinationals
The traditional fishing industry is doing more harm to the lake than fish cage farming, my brother.
Overfishing, incorrect fishing gear, and disregarding breeding seasons are among the issues affecting the lake’s ecosystem.
fish cage farming is the only way to go in promoting the economic empowerment of the people from the lake region. The so-called environmental experts are more often than not political weaponry deployed by their masters to derail the development of the region in the name of experts. now take this, it is estimated that over 20,000 fishermen go out at night for the omena fishing on the lake in the Kenyan side.
when nature calls, what do they do? They do it directly to the lake… that’s raw sewage every night to the lake…coupled with the wrong fishing gears that they use, I can confidently say that traditional fishing methods are more harmful to the lake ecosystem than the cage farming….anyway fish cage farming is not new….it’s a common practice in the developed world…so let’s copy the best practices from the successful cases but the cage farming MUST continue …no turning back
FISH FARMING HAS BEEN INTENSIVELY PRACTISED IN CHINA (CASE STUDY), SINCE 1970’S WITH TREMENDOUS SUCCESS. THERE, IT HAS GROWN IN A BIG INDUSTRY SUPPORTING LIVELIHOODS IN A BIG WAY. LET KENYA GOVERNMENT JUST DEAL WITH THE MAJOR CAUSES OF LAKE CONTAMINATION A RISING FROM LOCAL INDUSTRIES, COMMUNITIES AND THE KISUMU CITY, FIRST , BEFORE INTERFERING WITH LIVELIHOODS.
The debate on Cage Farming in Lake Victoria requires a broad spectrum perspective.
Several studies have shown that a greater proportion of the lake Pollution has been caused by industrial affluent, Agricultural surface runoff and sewerage system that have been directed to the Lake.
The decline and extinction of fisheries species in Lake Victoria were witnessed long ago before the invention of Cage Culture in Lake Victoria.
Such studies may be sponsored to fit a particular objective…Cage farming has proved to be a change maker in our society.
The debate on the lake pollution should be looked at wholly and right policies be formulated to curb and secure the lake from depletion of its ecological functions.
A wholistic approach to the ecosystem would be a priority. That was a good study though appear targeted. A separate study would be ideal on other potential pollutants: industrial, municipal, agricultural and domestic waste. The study should not only focus on fish but the rich aquatic biodiversity in the lake