Oropharyngeal morphology related to filtration mechanisms in suspension‐feeding American shad (Clupeidae)

Abstract

To assess potential filtration mechanisms, scanning electron microscopy was used in a comprehensive quantification and analysis of the morphology and surface ultrastructure for all five branchial arches in the ram suspension‐feeding fish, American shad (Alosa sapidissima, Clupeidae). The orientation of the branchial arches and the location of mucus cells on the gill rakers were more consistent with mechanisms of crossflow filtration and cross‐step filtration rather than conventional dead‐end sieving. The long, thin gill rakers could lead to a large area for the exit of water from the oropharyngeal cavity during suspension feeding (high fluid exit ratio). The substantial elongation of gill rakers along the dorsal‐ventral axis formed d‐type ribs with a groove aspect ratio of 0.5 and a Reynolds number of approximately 500, consistent with the potential operation of cross‐step filtration. Mucus cell abundance differed significantly along the length of the raker and the height of the raker. The mucus cell abundance data and the observed sloughing of denticles along the gill raker margins closest to the interior of the oropharyngeal cavity suggest that gill raker growth may occur primarily at the raker tips, the denticle bases, and the internal raker margins along the length of the raker. These findings will be applied in ongoing experiments with 3D‐printed physical models of fish oral cavities in flow tanks, and in future ecological studies on the diet and nutrition of suspension‐feeding fishes.

Hydrodynamic analysis of bioinspired vortical cross-step filtration by computational modelling

“…Intraoral structures that are backward-facing steps with d -type configurations in crossflow are found in an enormous diversity of suspension-feeding vertebrates ranging in size from tadpoles to whales [ 9 , 31 ]. This diversity provides rich opportunities to explore cross-step filtration using CFD.…”

Midtrophic fish feeding modes at the poles: an ecomorphological comparison of polar cod (Boreogadus saida) and Antarctic silverfish (Pleuragramma antarctica)

“…Based on the biomechanical characteristics and gill raker morphology, polar cod may be defined as a pump filter feeder (sensu Lazzaro 1987), capable of rhythmic suctions to capture prey items when prey items are small and/or present at high densities. Compared to the extremely effective and complex filter apparatus of herrings (Clupeiformes) that are specialized to feed on small-sized zooplankton (Storm et al 2020), the gill rakers of the polar cod and Antarctic silverfish are less dense, more spaced, and less numerous, supporting filter feeding as a possible alternative but not the main feeding mode of those species.…”

Formation of a fringe: A look inside baleen morphology using a multimodal visual approach

“…This cross‐flow filtration may work with a dead‐end sieve, or there may be pores larger than the particle size that are partially occluded by vortices induced by the tangential flow (vortical cross‐step filtration). In either case, the tangential shearing moves particles toward a collection point (Cohen et al, 2018; Storm et al, 2020). Cross‐flow filtration was suggested by J. Goldbogen et al (2007) as a possible mechanism of filtration in rorquals, due to the similarity of estimated flow speed and Reynolds number to that of suspension feeding fishes employing cross‐flow filtration (J. Goldbogen et al, 2007; Sanderson et al, 2001).…”

“…This cross-flow filtration may work with a dead-end sieve, or there may be pores larger than the particle size that are partially occluded by vortices induced by the tangential flow (vortical crossstep filtration). In either case, the tangential shearing moves particles toward a collection point (Cohen et al, 2018;Storm et al, 2020).…”