Variation in gill rakers of asian carp and native filter-feeding fishes from the Illinois, James and Wabash Rivers, USA

Abstract

Populations of silver (Hypophthalmichthys molitrix) and bighead carp (H. nobilis) may be controlled by targeting the structure of gill rakers - how they filter food particles from the water column. Because species-specific differences in gill raker structure were not well understood, I investigated the morphology and spacing of these structures in Asian carp and compared them to those in gizzard shad (Dorosoma cepedianum) and bigmouth buffalo (Ictiobus cyprinellus) -- two species of filter-feeding fish competing with Asian carp for food in the upper Mississippi River basin. Stereomicroscopy and a novel approach of confocal microscopy were used to examine the morphologies of gill raker from each species. Qualitative analyses indicated unique morphologies of rakers among all four species. Quantitative analyses of silver carp and gizzard shad indicated spacing of gill rakers in silver carp was correlated with fish length and did not generally differ among sampling sites or months. Spacing of gill rakers in gizzard shad was not correlated with fish length, but differed among sites and months. Thus, silver carp may be controlled with microparticles which target the length-dependent spacing of their gill rakers. Simultaneously, consumption of microparticles by gizzard shad may be minimized based on site-specific spacing of gill rakers.