Science-based f ish health management is a key component of sustainable aquaculture. Farmed tilapia provides an affordable source of animal protein and contributes significantly to many local economies. Lake Volta is a major area for tilapia farming in Ghana. While t here have been reports of disease events and high tilapia mortality in Lake Volta, the data are often scattered and unpublished . To address this , the Norwegian Veterinary Institute, University of Ghana and Fisheries Commission have conducted a baseline study to map the current disease situation in tilapia farms in Lake Volta.
Biological samples were collected from 31 selected farms along Lake Volta in Eastern and Volta regions of Ghana. Samples were screened for bacterial agents via bacterial colony morphology, staining and MALDI-TOF analyses. I nfectious spleen kidney necrosis virus (ISKNV) and tilapia lake virus (TiLV) were analysed via multiplex PCR and qPCR, respectively. Histopathological analyses are currently on going.
Streptococcus agalactiae was the predominant bacteria detected , and was mainly found in adult fish . To characterise the serotypes at affected farms, f urther sequencing is being conducted . This is expected to give an improved understanding of the serotypes circulating in the field relative to the serotypes targeted by the most co mmonly used conjugate autogenous vaccines. Other s ignificant bacterial pathogens included Edwardseilla tarda , Aeromonas spp., and Plesiomonas shiegelloides . ISKNV was widely distributed in the lake and was mainly found in fingerlings and juvenile fish. Co-infections with bacterial pathogens were common. TiLV was not detected in any sample.
Farm interviews revealed that most farms (93,5%) had experienced significant disease events in the past five years. Affected farms reported s ignificantly increased disease-associated mortality compared to baseline mortality, with disease-related mortality in many farms reaching 80% or above. Substantial financial losses were subsequently experienced. Improved diagnostic services, and more efficient vaccines and treatment options , were amongst specific improvements requested by farmers. The results from this study will be u tilised to inform laboratory capacity development prioritizations, biosecurity guideline developments and disease reporting and outbreak investigation protocols.
The study was f unded by the NORAD Fish for Development (FfD ) project, and supported by CEFAS through the University of Ghana PhD fellowship. The FfD project aims to enhance science-based sustainable management practices in Ghanaian aquaculture for long-term socio-economic benefits.