For generations, tinned tuna has fed families across Australia with quiet reliability, yet mercury has shadowed it like an uninvited guest at every meal. Science now offers some reassurance: the smaller fish species used in canning accumulate far less of the toxin than their larger ocean counterparts, and the amounts found in a typical tin sit well within the margins that regulators consider safe for adults and children alike. The deeper lesson here is not merely about mercury thresholds, but about how fear, once attached to a food, can outgrow the evidence that first gave rise to it.