Gillraker number, one of the most important taxonomic characters in the Coregoninae, has been considered genetically determined and not environmentally modifiable. However, laboratory-reared progeny of Coregonus alpenae, C. artedi, C. clupeaformis, C. hoyi, C. kiyi, C. zenithicus, and Prosopium cylindraceum generally had fewer gillrakers than the wild parents from which eggs were taken for hatching and rearing. Of 19 experimental groups hatched and reared between 1957 and 1996, only progeny from C. alpenae, C. zenithicus, and one group of C. clupeaformis had gillraker counts similar to their parents. All other groups had three to six gillrakers less than their wild parents. Most species were hatched and reared under similar conditions including similar temperatures, except for three groups of C. hoyi and several groups of C. clupeaformis and C. artedi. Incubation of C. hoyi eggs at 2°, 4°, and 8° C produced fish with five to six fewer gillrakers on average than their wild parental source in Lake Michigan. Warmer rearing temperatures produced higher gillraker counts in C. clupeaformis, and perhaps the discrepancies observed between wild and laboratory-reared fish in these experiments resulted from colder rearing temperatures in the laboratory than those experienced by wild fish.
