Complex sentence: The or sweetfish, "Plecoglossus altivelis", is an amphidromous fish, the only species in the genus "Plecoglossus" and family Plecoglossidae.
Split into simpler sentences: The or sweetfish, "Plecoglossus altivelis", is a species of fish. It is the only species in the genus "Plecoglossus" and family Plecoglossidae.