Variation in Gill Rakers of Silver Carp and Gizzard Shad from the Illinois, James and Wabash Rivers, USA

Controlling populations of silver carp Hypophthalmichthys molitrix may be possible by developing biocides captured in filterable microparticles. Because the size of particles removed by filter-feeding fishes is dependent upon the structure of their gill rakers, the rakers of silver carp were examined in comparison to those of native filter-feeding gizzard shad Dorosoma cepedianum. Confocal microscopy was used to compare intra- and inter-species variation in raker morphology. Gill rakers of silver carp correlated with fish length and did not generally differ among sites or seasons, suggesting that the size of particles removed from the water column during feeding is dependent upon the size of the fish and not location or season. Gill rakers of gizzard shad did not correlate with fish length but did differ among sites and seasons, suggesting that the size of particles removed by gizzard shad may be population-dependent and vary with location and season. The morphological differences in gill rakers between species suggests there may be the potential for designing microparticles to target specific sizes of silver carp, regardless of season or location. The geographic and seasonal variation in gizzard shad gill rakers suggests that some populations may be at greater risk of retaining microparticles than others.