Determinants of submerged macrophytes palatability to grass carp Ctenopharyngodon idellus

Submerged macrophytes reestablishment is one of key processes in restoration of water ecological system. However, adverse effect caused by grass carp on macrophyte communities is existed during the process of ecological restoration. At present, little is known about determinants of submerged macrophytes palatability to grass carp. In this study, we measured the relative consumption rates (RCR) of grass carp on four species of submerged macrophytes Hydrilla verticillata, Vallisneria natans, Ceratophyllum demersum, and Myriophyllum spicatum, analysed the correlation between macrophytes traits and RCR, then investigated the kinds of flavonoids in four species of submerged macrophytes and their effects on the palatability for grass carp. The results showed that RCR of grass carp on H. verticillata and V. natans were much higher than C. demersum and M. spicatum. And for each submerged macrophyte, RCR of grass carp declined in the order of July > October > May. Stepwise multiple liner regression analyses showed that water temperature and protein were positively correlated, and flavonoids were negatively correlated, with RCR of grass carp. Rutin, quercitrin, quercetin and kaempferol, as the typical kinds of flavonoids, were in different contents in four kinds of macrophytes. And rutin, quercetin and kaempferol can deter grass carp feeding. These results conducted that grass carp favoured macrophytes with high protein and ate less macrophytes with high flavonoids. And it is helpful to provide fundamental basis for administrators to select appropriate macrophytes in restoration of water ecological system.