Myxozoans are metazoan parasites which are highly pathogenic in commercially important
fish, particularly in aquaculture. Enteromyxosis is an economically significant disease
caused by the myxosporean parasite Enteromyxum leei.
Presently, early diagnosis of enteromyxosis in sharpsnout seabream was achieved by
monitoring fish on a time-scale scheduled basis in combination with a validated molecular
diagnostic technique. Two different successive fish batches of a commercial fish farm were
monitored starting from the first month of on-growing in sea cages until fish reached
commercial size. Fish weight and water temperature differentially ranged between them.
E. leei detection was performed both by classical microscopic
observation of fresh smears and by quantitative polymerase chain reaction (qPCR) while
prevalence, mean intensity and mortality rate were calculated. In total, 520 fish were
screened; 320 from the first batch and 200 from the second one. Parasitosis illustrated a
seasonal occurrence pattern (spring and summer). When qPCR was used as a diagnostic
method, enteromyxosis was diagnosed earlier with more increased prevalence compared to the
microscopic observation. In this case, the parasite was detected at the lowest water
temperature that has ever been recorded (14.7 °C), during the first month of on-growing in sea cages. The two-factor
combination of water temperature and fish weight proved to be the most significant factor
that could determine the emergence and development of parasitosis and smaller fish proved
to be more susceptible. Mortality was influenced by both prevalence and intensity of
parasitosis. An earlier diagnosis and identification of all developmental stages of the
parasite throughout its life cycle was verified with qPCR, significantly before any
outbreak occurred. The latter could become a key diagnostic tool for the control of
enteromyxosis, allowing stakeholders and fish farmers to adopt all necessary precautionary
measures minimizing economic loss in sharpsnout seabream intensive farming.