Marabous storks and other scavenging birds hunting for fish around cage fish farms of Lake Victoria. Credit: Wambi MichaelA dark storm clouds the future of aquaculture following growing scientific evidence that cage fish farming is negatively impacting native fish stocks in Lake Victoria.Cage culture is an open system that allows exchange of diseases and pathogens between cultured and native fish.The latest of such warnings was this month out of a review authored by the Executive Director of National Environment Authority, Barirega Akankwasah and six other experts at the country’s environment watchdog body. Warnings by Dr. Akankwwasah and others was published in the International Journal of Fisheries and Aquatic Studies titled “Environmental impacts of cage fish farming: A review”The experts say their review showed that cage fish farming presents a number of environmental challenges including, eutrophication, disease transmission, alterations in aquatic biota, and degraded water quality.“These issues threaten the ecological balance of aquatic ecosystems, which is important for the communities that depend on it. Therefore, too fully harness the potential of cage fish farming as a sustainable aquaculture strategy, it is important that future developments integrate advanced waste management and environmental monitoring systems. In doing so, the aquaculture sector can contribute not only to economic growth but also to the long-term sustainability and resilience of aquatic ecosystem” reads part of the review. Growing of fish in cages is currently practiced in Uganda and was first introduced in northern Lake Victoria in 2010.For example, in 8-12 m3 cage, one can raise one ton of fish in 8 months. The researchers note that whereas cage fish farming offers economic benefits, it also raises significant environmental concerns.“However, this review showed that cage fish farming presents a number of environmental challenges including, eutrophication, disease transmission, alterations in aquatic biota, and degraded water quality.”They warn that these issues threaten the ecological balance of aquatic ecosystems, which is important for the communities that depend on it.“Therefore, to fully harness the potential of cage fish farming as a sustainable aquaculture strategy, it is important that future developments integrate advanced waste management and environmental monitoring systems. In doing so, the aquaculture sector can contribute not only to economic growth but also to the long-term sustainability and resilience of aquatic ecosystems.”It has been noted in other studies that like other animal production sectors, aquaculture produces waste, and managing the waste from fish farming is both challenging and costly, as it disintegrates and becomes diluted in the culture water.Waste generated from uneaten fish feed and faecal matter from cage farms lead to increased nutrient loading in surrounding waters.In January 2021, residents around Bugonga and Kigungu landing sites together with those at Wagagi Flower Farm and Lido beach all in Wakiso woke up to find hundred dead fish washed to the shores.It suspected the deaths could have been due to poisoning. ed It is emerging that cage fish farms produce and release wastes rich in nitrogen and phosphorus into the water column and bottom sediments. High nutrient inputs lead to eutrophic conditions characterized by phytoplankton blooms, high ammonia building in the water.Studies have found that ammonia is toxic to all vertebrates causing convulsions, coma and death.Others have disputed this. It is generally believed that high ammonia levels cause fish deaths by making it hard for them to breathe and that it damages their gills and internal organs.This is the second scientific review warning about cage fish farming on Lake Victoria in less than two months.Another study titled “Nile Tilapia (Oreochromis niloticus L.) Cage Aquaculture in Africa: Potential Threats to Congeneric Fish Species and Advances to Detect Escapes highlighted the ecological and genetic threats posed by O. niloticus cage aquaculture in Africa, particularly competition with native species, hybridisation and inadequate regulatory frameworks.Cage fish culture in Lake Victoria: A boon or a disaster in waiting?Another study by researchers from Kenya Marine and Fisheries Research Institute titled “Cage fish culture in Lake Victoria: A boon or a disaster in waiting?” confirmed a buildup of ammonia around the cages ranged between 0.14 and 0.2 mg/L. It said the increase in ammonia near the cages was attributed to the protein in uneaten food and fish waste that had been broken down into ammonia and nitrite.“Ammonia can be extremely toxic to fish, with toxic levels of unionised ammonia ranging from 0.6 to 2.0 mg/L in the case of tilapia. Unionised ammonia begins to depress appetite of this fish species at concentrations as low as 0.08 mg/L,” said the researchers.They also found that that fish exposed to low levels of ammonia over time were more susceptible to bacterial infections and have poor growth.“Recorded fish kills equivalent to about US$ 4,300 occurred in the cages in Lake Victoria in 2016; this was attributed to low dissolved oxygen concentrations, although a combined effect, involving ammonia and oxygen, is possible.”From the Kenyans research, cage culture in Lake Victoria is a promising blue growth venture, however, for cage farming to be a success, an effective policy framework for lake-zonation is needed to ensure that all stakeholders use the lake without impinging on the development opportunities of others. It further states that with lack of proper policy guidelines and management practices in place, cage farming is likely to be an environmental disaster.The post Cage Fish Culture In Lake Victoria: A Disaster In Waiting? appeared first on Business Focus.