Aquaculture is a vital livestock activity that provides food, nutrition, and employment worldwide. Among the most extensively farmed fish is the rainbow trout, reaching yields of 959.6 thousand tonnes in 2020 globally. In Peru, rainbow trout is the most produced fish species, achieving a yield of 61,572.8 tonnes in 2022, although the majority of the production (78.25%) is destined for the domestic market. However, the sustainability of the Peruvian rainbow trout farming industry is at risk, as continuous cases of morbidity and mortalities are reported by producers during standard screening programs. Samples of dead and moribund fish with clinical signs indicative of aeromonosis were collected and analysed in the Laboratorio de Patobiología Acuática, Instituto del Mar del Perú (IMARPE) in Callao, Peru.
Molecular analysis revealed the presence of A. sobria (n=12), A. salmonicida (n=3), A. popoffii (n=12) and A. media (n=1). Biochemical characterisation and the examination of virulence factors revealed the presence of ‘atypical’ A. salmonicida in Peruvian aquaculture. Experimental infection revealed mortalities of up to 100% for A. salmonicida (7.2 x 106 & 7.2 x 107 CFU/fish), while A. sobria, and A. popoffii (4 x 107 CFU/fish) were limited to 40% and 20% mortalities, respectfully., in intraperitoneally infected fish. Clinical signs were only observed in individuals infected with A. salmonicida, (Figure 1).
This is the first molecular confirmation of Aeromonas spp. in Peruvian farmed trout, and of A. popoffii provoking mortalities in fish. The gene virulence profiles of all isolates lacked any noticeable correlation between mortality and any single, or combination of genes (Table 1). Further studies with other genes, including the type 3 secretion system (T3SS), are recommended. Presently, no commercial vaccines against Aeromonas spp. are available in Peru. We recommend the development of a polyvalent vaccine that includes all mortality-inducing Aeromonas species to improve the sustainability of trout farming in Peru.