Emerging fungal and oomycete diseases in cage-cultured nile tilapia (oreochromis niloticus) in Lake Victoria: current knowledge and future priorities

Aquaculture plays an increasingly important role in global food security, particularly in East Africa, where cage culture of Nile tilapia (Oreochromis niloticus) in Lake Victoria has expanded rapidly over the past decade. However, the sustainability of this production system may be threatened by emerging fungal and oomycete diseases that remain poorly understood in the region. This review synthesizes current knowledge on fungal and oomycete infections potentially affecting cage-cultured Nile tilapia in Lake Victoria, with particular emphasis on five key pathogens: Aphanomyces, Saprolegnia, Branchiomyces, Fusarium, and Exophiala species. Following PRISMA guidelines, a systematic literature search of PubMed, Web of Science, Scopus, Google Scholar, and EMBASE databases covering the period 2000–2025 identified 1,200 records. After duplicate removal and eligibility screening, 85 full-text studies were included in the final review. Of these, only 15 studies (17.6%) specifically addressed Lake Victoria or its immediate basin, highlighting a substantial regional knowledge gap. Available evidence indicates that fungal and oomycete pathogens may contribute to fish morbidity and mortality, particularly under conditions of poor water quality, environmental degradation, high stocking densities, and other stressors common in intensive aquaculture systems. Reported clinical manifestations include skin ulceration, cotton-like lesions, gill necrosis, granulomatous inflammation, and respiratory impairment. Although Fusarium and Exophiala species are recognized as opportunistic pathogens of potential public health relevance, there is currently no direct evidence of fish-to-human transmission within the Lake Victoria region; occupational exposure through contaminated water, biofilms, and handling of infected fish remains the more plausible route of concern. This review further identifies major gaps in diagnostic capacity, fragmented transboundary disease surveillance across Tanzania, Kenya, and Uganda, and limited farmer awareness regarding disease recognition and affordable control measures. Overall, the findings emphasize the urgent need for baseline epidemiological studies, standardized diagnostic protocols, antifungal resistance monitoring, and integration of fungal disease surveillance into One Health frameworks to support sustainable aquaculture development in East Africa.