The fish parasites Saprolegnia spp. (Oomycota) and Amyloodinium ocellatum
(Dinophyceae) cause important losses in freshwater and marine aquaculture industry,
respectively. The possible adverse effects of compounds used to control these
parasites in aquaculture resulted in increased interest on the search for natural
products with antiparasitic activity. In this work, eighteen plant-derived compounds
(2′,4′-Dihydroxychalcone; 7-Hydroxyflavone; Artemisinin; Camphor (1R); Diallyl sulfide;
Esculetin; Eucalyptol; Garlicin 80%; Harmalol hydrochloride dihydrate; Palmatine
chloride; Piperine; Plumbagin; Resveratrol; Rosmarinic acid; Sclareolide; Tomatine,
Umbelliferone, and Usnic Acid) have been tested in vitro. Sixteen of these were
used to determine their effects on the gill cell line G1B (ATCC®CRL-2536TM) and
on the motility of viable dinospores of Amyloodinium ocellatum, and thirteen were
screened for inhibitory activity against Saprolegnia spp. The cytotoxicity results on
G1B cells determined that only two compounds (2′,4′-Dihydroxychalcone and Tomatine)
exhibited dose-dependent toxic effects. The highest surveyed concentrations (0.1 and
0.01mM) reduced cell viability by 80%. Upon lowering the compound concentration
the percentage of dead cells was lower than 20%. The same two compounds
revealed to be potential antiparasitics by reducing in a dose-dependent manner the
motility of A. ocellatum dinospores up to 100%. With respect to Saprolegnia, a
Minimum Inhibitory Concentration was found for Tomatine (0.1mM), Piperine and
Plumbagin (0.25mM), while 2′,4′-Dihydroxychalcone considerably slowed downmycelial
growth for 24 h at a concentration of 0.1mM. Therefore, this research allowed to
identify two compounds, Tomatine and 2′,4′-Dihydroxychalcone, effective against both
parasites. These compounds could represent promising candidates for the treatment of
amyloodiniosis and saprolegniosis in aquaculture. Nevertheless, further in vitro and in
vivo tests are required in order to determine concentrations that are effective against the
considered pathogens but at the same time safe for hosts, environment and consumers.
