"A fish with a glass eye" sounds like the punch line to a joke that starts with an angler and an ophthalmologist walking into a bar. But two rockfish at the Vancouver Aquarium are now sporting bright yellow ocular prosthetics. The fish, which each lost an eye to disease, were restored to their former good looks by the operation. The primary goal, however, was to prevent them from being harassed by other fish, which seem to view an empty eye socket as a sign of weakness, said Seattle Aquarium veterinarian Dr Lesanna Lahner. "There's an aesthetic piece, but my main concern is fish health," said Lahner. A handful of fish at the Seattle Aquarium have also received the implants, and Lahner assisted Vancouver vets with their one-eyed rockfish last month. The staff at the British Columbia aquarium were particularly worried about a copper rockfish that had an eye surgically removed after a cataract rupture. The 2.7kg fish started avoiding its tank mates and hiding in nooks and crannies, said Dr Martin Haulena, the aquarium's head veterinarian. "Fish were picking at it," he said. "Its fins were tattered, and it was really getting banged up." With life spans that can exceed a century in the wild, quality of life is particularly important for captive rockfish. During the 20-minute procedure, a technician bathed the anaesthetised animal's gills and skin with water, while Lahner popped the prosthetic into the socket and coached Haulena on the best way to thread fishing line through bone to hold it in place. The glass eyes are the kind taxidermists use in trophy trout and salmon mounted for display. Lahner glues two of the flat-backed inserts together to form a sphere. Fish with a missing eye used to be routinely euthanised at aquariums because they were considered unsightly, Haulena said. Since getting its new eye, the Vancouver copper rockfish seems to be back to its old self, Lahner said.