Motile Aeromonas Septicemia (MAS), hemorrhagic septicemia, ulcer disease, red-sore disease, or infectious dropsy are diseases that are caused by A. hydrophila complex (Mzula et al., 2019). The bacteria are normally inhabitant in the aquatic environment and the gastrointestinal tract of the healthy animal. Therefore, various motile aeromonads species are reported as stress related pathogen resulting in disease outbreaks and huge mortality in wild and cultured freshwater fishes (Youssuf et al., 2020). In addition, A. hydrophila has been reported in reptiles, amphibians, cattle, and humans worldwide.

The highest prevalence of aeromonas isolates from infected fishes that cause 80-100% modalities are reported to be A. hydrophila, A. jandei and A. veronii (Abdelsalam et al., 2021) Horizontal transmission via ingestion of contaminated food or direct contact with infected fish are the main route of MAS infection. Additionally, homologues co-infections of Aeromonas with other bacteria such as A jandaei and A. veronii (Dong et al., 2017), or heterologous co-infection as Aeromonas sp. and Streptococcus sp (Sukenda et al., 2017), A. veronii and Flavobacterium columnare (Dong et al., 2015), A. hydrophila and Tilapia Lake virus (Nicholson et al., 2020) are considered an important cause for enormous mortalities of tilapia farms.

In Egypt, Aeromonas species have been reported from Nile tilapia suffering from summer mortality syndromes (Matter et al., 2018; Youssuf et al., 2020).