Relationship between the chemical composition of aquatic macrophytes and their consumption by grass carp, Ctenopharyngodon idella

The rate at which triploid grass carp, Ctenopharyngodon idella , consumed two plant species from different locations was measured and compared to the chemical composition of the plants. Grass carp fed on Elodea canadensis from three lakes at significantly different rates ( P > 0.001), but did not eat Elodea densa from two of the sites at different rates. Feeding rate of the grass carp was positively correlated to the concentration of calcium ( r = 0.976) and lignin ( r = 0.946), but negatively correlated to the content of iron ( r =−0.808), silica (r=‐0.934) and cellulose ( r =−0.922). Multiple regression analysis revealed that calcium and cellulose content were the most important predictors of consumption rate. These experiments demonstrate that water chemistry may affect palatability and could in part be responsible for some of the discrepancies in grass carp consumption rate and preference studies.