Monogenean infection of the internal organs is extremely rare when
compared to external infections. This study describes mass mortality of
Nile tilapia (Oreochromis niloticus L.) originating from
co-infection with Enterogyrus spp. and Aeromonas jandaei
following transport stress. The first fish deaths occurred on day 1
post-transport, while cumulative mortality reached approximately 90% by
day 10 post-stocking. An atypical amount of pale (whitish) faeces
floating on the surface of the water as well as typical clinical signs
of motile Aeromonas septicemia, were reported. Adult monogeneans and
countless eggs of monogeneans were found in the stomachs and the
intestines of both moribund and dead fish, respectively. Two strains of
A. jandaei were isolated from the kidneys. Scanning electron
microscope microphotographs of the stomach revealed the presence of
numerous monogeneans penetrating deep into the gastric tissue, and
diffuse lesions filled with bacilliform bacteria. This is the first
report of co-infection by Enterogyrus spp. and A. jandaei
in Nile tilapia and the first report of E. coronatus, E.
foratus, and E. malbergi parasitizing tilapia in Brazil. These
findings indicate that synergic co-infection by Monogenean stomach
parasites (E. coronatus, E. foratus, and E.
malbergi) and A. jandaei may induce high mortalities in tilapia
following transport stress.