There were plenty of oral reports of fishermen being overcome by a violent seizure when sorting through a netted catch. They knew which fish it was, they just had no concept of electricity yet. It took a scientist from the Royal Society in London - can't recall his name - to link the fish with electricity, he and his colleagues were astonished that a living creature could biologically produce such an electric discharge as intense as a Leyden Jar (a rudimentary precursor to Volta's invention of the battery as we still know it today).