A Comparison of Native and Exotic Hosts for the Silver Lamprey
Philip A. Cochran
Abstract.—Silver lamprey Ichthyomyzon unicuspis has been most strongly associated with native host species that are relatively large and have naked skin or relatively small scales, including paddlefish Polyodon spathula, lake sturgeon Acipenser fulvescens, lake trout Salvelinus namaycush, ictalurid catfishes, and esocids. In many regions, however, and especially in the southern part of the silver lamprey’s geographic range, these host species have declined in abundance through a combination of human impacts, and the most abundant large fish species is now the common carp Cyprinus carpio, an exotic species with large scales. Silver lampreys removed from paddlefish in the Wisconsin River and allowed to feed on carp in the laboratory displayed very little growth relative to lampreys in the river. Although paddlefish lack scales, skin densities of carp and paddlefish, measured as dry mass per unit area, were similar. However, dried samples of paddlefish skin displayed a substantial lipid residue, and skin density of paddlefish expressed as ash weight was less than that of carp. It is likely that increased handling time contributes to reduced growth by silver lampreys on carp. The importance of paddlefish skin lipids to silver lamprey feeding ecology should be investigated.