The Mekong Delta is the most productive region for fish farming in Vietnam. In recent years, the production of red tilapia (Oreochromis sp.) in floating cages along the rivers has increased. Red tilapia are mainly used for consumption at local markets. Little is known about the variety and occurrence of pathogens in red tilapia farming. This study evaluated pathogen occurrence at four time intervals between June 2014 and February 2015 within one production crop of red tilapia farming on 2 farms per province in Ben Tre, An Giang, Dong Thap, and Vinh Long. Pathogens including Streptococcus sp., Aeromonas sp., Flavobacterium sp., and Trichodina/monogenean parasites were observed. Prevalence (existing cases) and incidence (new cases) of these pathogens are discussed.