Epizootic Disease Dynamics and Their Implications for Biosecurity Policy in Nigerian Catfish Aquaculture: A Complex Systems Analysis

This research analysed the dynamics of epizootic disease events in Nigerian catfish aquaculture systems using a complex systems analytical framework, developing original biosecurity policy recommendations grounded in network epidemiology and systems thinking. Disease epizootics represent the single largest source of uninsured production loss in Nigerian catfish aquaculture, yet the epidemiological pathways, transmission networks, and systemic vulnerabilities driving outbreak severity have not been formally characterised. The study combined a national survey of epizootic events in catfish farms across 18 states over a three-year period, collection of disease agent samples for bacteriological and virological characterisation, and construction of a farm-level disease transmission network model using geographic and commercial linkage data. Agent-based epidemic simulation was calibrated to observed outbreak data and used to test the efficacy of alternative biosecurity interventions under realistic Nigerian farming conditions. Bacteriological analysis identified Aeromonas hydrophila and Edwardsiella anguillarum as the dominant primary pathogens in epizootic events, with viral co-infections detected in 23 percent of severe outbreaks. Network analysis revealed that fingerling trade was the primary inter-farm transmission pathway, with hatchery source networks exhibiting scale-free topology in which a small number of high-connectivity hatcheries disproportionately seeded regional outbreaks. Simulation results demonstrated that targeted biosecurity interventions at high-connectivity hatchery nodes reduced simulated epidemic size by 74 percent compared to uniform farm-level interventions alone. A fingerling movement certification scheme was identified as the single most cost-effective systemic intervention. The research delivers a complex systems biosecurity analysis with direct policy application and recommends the national implementation of a catfish fingerling certification and movement monitoring scheme as a cornerstone of Nigerian aquaculture biosecurity infrastructure. Keywords: epizootic disease, catfish aquaculture, biosecurity policy, network epidemiology, complex systems