Survey on the most common bacterial pathogens of the nile tilapia fries in Kafr El Sheikh Governorate, Egypt

Abstract

Recently, aquaculture in Egypt has faced multiple records of mass mortality resulting in high economic losses. The mass mortality among tilapia fries is mostly attributed to bacterial pathogens either with or without other pathogens. This study is designed to investigate the etiological factors implicated in mortality of the Nile tilapia fries. Bacteriological examination of the Nile tilapia fries including isolation and identification using a range of techniques (API NE20, Vitec, PCR and 16SrRNA Sequencing) revealed an array of typical pathogens known to cause lethal infections in tilapia. The most frequently isolated strains were Aeromonads 33.3% (A. veronii, A. sobria, A. hydrophila), Staphylococcus epidermidis, 11.1 % Pseudomonas aeruginosa, 11.1% and Shigella sonnei 11.1%. Furthermore, three emerging freshwater aquaculture pathogens which have zoonotic significance, namely Providencia rettgeri (11.1%), Shewanella putrefaciens (11.1%) and Acinetobacter lwoffii (11.1%) were isolated from fish fries. Despite known pathogenicity, inoculation of fish fingerlings with the different bacterial isolates resulted in only mild mortality rates under non-stress conditions, emphasizing the role of additional environmental stressors in triggering mass mortality of juvenile fish. Conclusively, these pathogens have a significant negative impact on tilapia fries, particularly in combination with environmental stress.