By KT Reporter
A study involving a number of Ugandan researchers says cage fish farming widely being carried out on Lake Victoria is raising concern over potential biodiversity loss, genetic dilution and ecosystem disruption.
Titled “Nile Tilapia (Oreochromis niloticus L.) Cage Aquaculture in Africa: Potential Threats to Congeneric Fish Species and Advances to Detect Escapes”, the review was on Tuesday published on Free access online library Wiley.
It highlights the ecological and genetic threats posed by O. niloticus cage aquaculture in Africa, particularly competition with native species, hybridisation and inadequate regulatory frameworks.
Nile Tilapia or Oreochromis niloticus L. is the commonly known as ngege in Luganda and many dialects around the country.
Researchers were from different reputable bodies including the Institute of Integrative Nature Conservation Research, Department of Ecosystem Management, Climate and Biodiversity, BOKU University, Vienna, Austria, Kachwekano Zonal Agricultural Research and Development Institute (KAZARDI), National Agricultural Research Organization (NARO), Kabale, Department of Animal and Fisheries Sciences, Maseno University, Maseno, Kenya, College of Natural Sciences, Makerere University, Kampala, Uganda, Bulindi Zonal Agricultural Research and Development Institute, National Agricultural Research Organization (NARO), Hoima and National Fisheries Resources Research Institute (NaFIRRI)-Aquaculture Research and Development Centre Kajjansi (ARDC).
They note that while cage aquaculture contributes to increasing fish production, the unintentional and intentional release of farmed fish into natural water bodies raises concerns about biodiversity loss, genetic dilution and ecosystem disruption.
They suggest a need to evaluate the long-term genetic and ecological consequences of interbreeding, including the loss of local adaptations and shifts in the ecological balance of affected water bodies and the development and application of advanced genetic monitoring.
“As cage aquaculture continues to expand, proactive research, strict regulation and continuous monitoring are essential to mitigate adverse genetic and ecological consequences while ensuring that aquaculture remains a viable and sustainable sector in Africa” read part of the review.
Cage fish farming, a recent development in aquaculture, has enhanced fisheries production due to its higher stocking densities than traditional pond and open-water systems.
The researchers says although it can enhance production, the system can pose biodiversity threats when there is an unintentional or intentional release of stocked fish into the wild.
They examined the expansion of Nile tilapia (Oreochromis niloticus L.) cage aquaculture in Africa and the potential threats that this may have on congeneric Oreochromis species. “Threats such as interspecific competition, disease transmission and hybridisation, which are drivers of genetic diversity loss among native fish populations, have been reported” it said.
They note that while direct evidence of hybridisation due to cage fish farming is lacking, genetic mixing of Nile tilapia with native Oreochromis species has been reported in some African water bodies.
Further, they said only Egypt, Kenya and Uganda have functional Fisheries and Aquaculture regulations for guiding the aquaculture activities.
“Thus, there is an urgent need to institute regulatory frameworks that not only provide clear guidelines on aquaculture production but also balance between environmental conservation and economic sustainability”.
Cage aquaculture in Uganda and Tanzania was started around 2006that is when rumors spare that President Museveni had sold Lake Victoria.
In Uganda, the researchers found that the selective breeding efforts of O. niloticus are uncoordinated, with little evidence of selection for improved performance reported by various stakeholders, including hatchery operators and researchers.
They noted that studies indicated that challenges faced by O. niloticus hatcheries include issues of inbreeding, hybridisation of closely related stocks and the presence of low-quality broodstock.
The findings from a 2018)showed that the aquaculture sector in Uganda still struggles with expensive fish feeds, predators and water quality issues due to increasing urbanisation. These problems arise from the absence of adequate selective breeding plans or initiatives for improving strains in broodstock development.
The authors further noted that O. niloticus from Lake Turkana (Kenya) are genetically divergent from their Ugandan populations, with the species in Lake Victoria showing genetic substructure.
“Such genetic substructures are likely indicators of historical isolation, restricted gene flow or localised environmental pressures, all of which can contribute to the differentiation of subpopulations within a species’ native range” it said
“This is not surprising given that in the early years of O. niloticus aquaculture, many hatcheries around most of these natural waterbodies used and still use broodstock, eggs or fingerlings originating from these ecosystems. Therefore, it is evident that some wild O. niloticus stocks may have already been affected by escapees” they concluded-URN. Give us feedback on this story through our email: kamwokyatimes@gmail.com
