![]() ![]() The inner face (where particles are ultimately collected) is composed of a net-like matrix with uniformly sized mesh (∼45 µm wide) spanning the surface. In addition, the inner and outer faces of the filtering plates are morphologically distinct. Early in ontogeny, individual gill rakers stitch together, creating a mesh-like plate that continues to fuse together with secondary dermal bone modifications ( Cohen and Hernandez, 2018). The filtering apparatus of silver carp is composed of two solid filtering plates that extend dorsally from the branchial arches ( Fig. 1A). The gill rakers of silver carp are morphologically distinct from those of previously described chondrichthyan or bony fishes, including those of bighead carp. Cohen and Hernandez (2018) hypothesized that the greatly modified filtering apparatus of silver carp aids in the capture of particles so small that they are generally only consumed by invertebrates. In particular, silver carp feed on a broad range of particle sizes from 4 to 85 µm ( Cremer and Smitherman, 1980 Battonyai et al., 2015 Zhou et al., 2009), making them an effective competitor for planktonic resources in the eutrophic rivers of the Mississippi River basin ecosystem ( Freedman et al., 2012). ![]() Silver and bighead carp ( Hypophthalmichthys nobilis) pose a significant threat to these freshwater ecosystems because they outcompete native species across the trophic hierarchy ( Solomon et al., 2016). Silver carp, Hypophthalmichthys molitrix, is a filter-feeding cyprinid from Eastern China and Siberia that is a major focus of aquaculture efforts worldwide and has proven to be highly invasive in the Mississippi River basin and other drainages in Europe, Asia and Africa ( Solomon et al., 2016 Cremer and Smitherman, 1980). Moreover, we found that absolute vorticity magnitude in silver carp is an order of magnitude greater than in bighead carp. This strong vortical organization is maintained only at 0.75 body lengths s −1, and vortical flow is poorly developed and maintained at slower and faster speeds. The organized vortical flow established by silver carp likely increased the number of interactions that the particle-filled water had with the filtering membrane. Filtering plates in silver carp induce strong directed vortical flow, whereas the filtering apparatus of bighead carp resulted in a type of haphazard cross-flow filtration. Using 3D particle image velocimetry, we determined how particles and fluid interact with the surface of the gill rakers/plates. Bighead carp are also invasive filter feeders, but their filtering apparatus is morphologically distinct from that of silver carp. Here, we investigate the underlying morphology and concomitant hydrodynamics that support the filtration mechanisms of silver and bighead carp. The filtering apparatus of silver carp comprises rigid filtering plates where the outer anatomy of these plates is characterized by long parallel channels that change in orientation along the length of the plate. Silver carp utilize modified gill rakers to capture a specific range of food however, their greatly modified filtering morphology allows them to feed on phytoplankton and zooplankton ranging in size from 4 to 85 µm. Invasive silver carp are thriving within eutrophic environments in the United States, in part because of their highly efficient filter-feeding mechanism. ![]()
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