eSHa alx is a medication for freshwater fish affected by parasitic crustacean species (Maxillipoda) such as Argulus (fish louse), Lernaea (anchor worm), Ergasilus (gillworm), and Salmincola (copepod). These parasitic crustaceans attach themselves to or within the fish's skin, as well as its gills. They can often be seen with the naked eye.