Parasitic infections are a persistent headache for fish farmers across Africa, and Egypt’s aquaculture sector feels it most acutely. African catfish (Clarias gariepinus), a species that matters for food security across the continent, has been hammered by a trematode parasite called Prohemistomum vivax. Recent work on praziquantel bath treatments has turned up some compelling results. The Scale of the Problem Start with the numbers. On commercial catfish farms in Egypt, infection rates for P. vivax have hit 86.6 percent in some surveys. Nearly nine out of ten fish carrying these parasites. The metacercariae—the encysted larval stage—burrow into muscle and internal organs, causing tissue damage, stunted growth, and mortality. Infected fish turn emaciated, produce…