Amyloodinium ocellatum
The dinoflagellate is endemic in temperate and tropical areas, and is capable of successfully adapting to a variety of different environments and to a great number of hosts, having been identified in four phyla of aquatic organisms: Chordata, Arthropoda, Mollusca and Platyhelminthes.
The parasite represents a serious problem for both reared and aquarium fish, since amyloodiniosis, the infection caused by this protozoan, can lead the host to death in less than 12 hours, with acute morbidity and mortality around 100%.
[1] In general, amyloodiniosis is typically present in land- or lagoon-based rearing sites (valliculture or inland brackish farming), where shallow seabeds and poor water exchange/recirculation allow the parasite to reach its optimal proliferation values.
In this phase, the protist is pear-shaped, enclosed in a cellulose wall and exhibits specific structures, rhizoids (tentacle like processes) that enable it to strictly anchor to host epithelia (gill or skin predominantly).
Constantly moving while anchored and therefore causing physical injuries to cells, trophonts inflict serious damages to the host, potentially inducing its death in 12-48 hours as a function of the parasite burden.
Based on data in the literature, the trophont feeds directly from the host cells, probably using the stomopode[clarification needed] by releasing digestive enzymes,[3] which exacerbate the rhizoid lesions.
In this phase, the protozoan is round and encapsulated in a cellulose wall, which becomes thicker and confers upon it an exceptional resistance to unfavourable conditions and to several therapeutic treatments.
[3] They inflict moderate-to-intense tissue reactions associated with serious gill hyperplasia, inflammation, haemorrhages and necrosis with subsequent death in less than 12 hours in heavy infected specimens.
Another clinical sign of amyloodiniosis could be the dusty appearance of the skin (hence the name "marine velvet disease"), as in European sea bass, but not in all fish species.
Depending on interactions with farming typology, parasite burden, fish species and season, amyloodiniosis can lead the host to death in less than 12-48 hours, with acute morbidity and mortality around 100%.
Generally, the infection affects land- or lagoon-based rearing sites (valliculture or inland brackish farming), whose characteristics (shallow seabeds and poor water exchange/recirculation) enable the parasite to best express its virulence.
Recently developed molecular approaches (PCR and LAMP) have been proven to provide early detection of dinoflagellates in water and gill tissue samples, even when the parasite is present at lowest concentrations, such as in subclinical infections.
Early diagnosis followed by a prompt treatment is crucial as the protozoan has exponential reproductive potential in the warmest months, temperature affects how quickly the parasites multiply.
It is important to emphasise that dinospores can be transported through aerosol droplets,[9] therefore contaminating farm equipment and/or contiguous ponds/tanks as well as nearby facilities if spread by strong winds.
An alternative to this protocol, based on in vitro maintenance of tomonts' in a hibernation status, was recently developed by a group of researchers of the University of Udine within the Horizon2020 Project ParaFishControl.
