For fish farmers of the gilthead sea bream in the Mediterranean, enteromyxosis is a particularly serious disease. Caused by the protozoan Enteromyxum leei, it causes significant stock losses. Despite the economic importance of the disease, there are large gaps in the knowledge about the pathology of this parasite which the EU project MYXFISHCONTROL aimed to elucidate. Project partners at Consejo Superior de Investigaciones Científicas in Spain used the Polymerase chain reaction (PCR) technique in two main research areas, both affecting the spread of the parasite. Firstly, it is highly important to diagnose if the disease is present in stocks. An infection means that husbandry must be changed to avoid stress such as handling. Also, all infected brood stock must be removed. The scientists found that for both lethal and non-lethal PCR, L-PCR and NL-PCR respectively, the sensitivity and specificity were outstanding. Furthermore, they outperformed the gold standard histology diagnosis. It was therefore recommended that the NL-PCR be applied as a routine test for monitoring the infectivity status for enteromyxosis. The other strand to the research involved the life cycle of the protozoan and the possibility of an intermediate invertebrate host. The scientists screened 350 invertebrate samples from around infected farms using PCR. These included sea anemones, corals, polychaete worms and crustaceans. Just over one percent of the samples were positive for E. leei indicating that there is no intermediate invertebrate host. Valuable information regarding the spread and diagnosis of this parasite is good news for the mariculture industry. As the disease is transmissible to various wild species, commercially important fish in marine ecosystems can be protected also. Fast accurate diagnosis also means that areas free of the parasite can be designated for the benefit of consumer and farmer.