During the experiments, we observed that while the uninfected controls remained healthy (these were the cultures with no addition of humic substances or salt), the flagellate-infected controls suffered mortalities.To try to reduce subsequent mortalities, infected cultures were treated with either: (i) humic substances (as 25 mg L− 1 DOC) because they can reduce growth and survival of aquatic parasites and pathogens (Meinelt et al., 2007 and Meinelt et al., 2008), or (ii) sea salt (as 4 g L− 1 sea salt), because salt is commonly used to treat ectoparasitic infections in fish; the concentration was well within the previously documented tolerance range of the M. macrocopa clone we studied ( Suhett et al., 2011). During the 10 day treatment period, live and dead cladocerans were counted every second day, and dead individuals removed, as described above.