The addition of humic substances was ineffective against the flagellates affecting the Moina, although humic substances can reduce growth and survival of some aquatic parasites and pathogens ( Meinelt et al., 2007 and Meinelt et al., 2008), and increase lifespan of hosts. However, the addition of 4 g L− 1 sea salt, a concentration well within the tolerance range of the clone (Suhett et al., 2011), resulted in significantly reduced host mortality. We presume that the flagellates were sensitive to the change in osmolarity, which in turn reduced their viability, and thus their damaging effects to the cladocerans.