Olfactory flow in the sturgeon is externally driven

Abstract

Fluid dynamics plays an important part in olfaction. Using the complementary techniques of dye visualisation and computational fluid dynamics (CFD), we investigated the hydrodynamics of the nasal region of the sturgeon Huso dauricus. H. dauricus offers several experimental advantages, including a well-developed, well-supported, radial array (rosette) of visible-by-eye olfactory sensory channels. We represented these features in an anatomically accurate rigid model derived from an X-ray scan of the head of a preserved museum specimen. We validated the results from the CFD simulation by comparing them with data from the dye visualisation experiments. We found that flow through both the nasal chamber and, crucially, the sensory channels could be induced by an external flow (caused by swimming in vivo) at a physiologically relevant Reynolds number. Flow through the nasal chamber arises from the anatomical arrangement of the incurrent and excurrent nostrils, and is assisted by the broad, cartilage-supported, inner wall of the incurrent nostril. Flow through the sensory channels arises when relatively high speed flow passing through the incurrent nostril encounters the circular central support of the olfactory rosette, decelerates, and is dispersed amongst the sensory channels. Vortices within the olfactory flow may assist odorant transport to the sensory surfaces. We conclude that swimming alone is sufficient to drive olfactory flow in H. dauricus, and consider the implications of our results for the three other extant genera of sturgeons (Acipenser, Pseudoscaphirhynchus and Scaphirhynchus), and for other fishes with olfactory rosettes.

The functional nasal anatomy of the pike, Esox lucius L.

“…Fig. 5C of Garwood et al, 2019) was found over 12 s to vary by < 0.02 %. Velocities, static pressures, and shear stresses were the averages of the last 500 iterations from a total of 2000 iterations of a converged, time-averaged solution to the Navier-Stokes equations.…”

“…Most of the methodology used here has been described before (Cox, 2008;Abel et al, 2010;Holmes et al, 2011;Howard et al, 2013;Ramsey et al, 2015;Garwood et al, 2019). We therefore give only brief descriptions here.…”

“…Surface models of the heads of the juvenile and adult pike were generated with the image processing software ScanIP (Synopsys, Mountain View, USA) as previously described (Garwood et al, 2019). We prepared two types of surface model: 'wild type' models (Fig.…”

“…We tackled these questions using the complementary techniques of dye visualisation and computational fluid dynamics (Garwood et al, 2019). The anatomically-accurate models employed in our experiments were derived from X-ray micro-computed tomography scans of two well-preserved specimens whose nasal anatomy differs in several important age-related respects.…”

“…We also compare olfactory flow in the pike with that in the sturgeon. We do so because the sturgeon's nasal 4 region is like that of the pike (Cox, 2008), and because flow through the nasal chamber of the sturgeon is externally-induced (Garwood et al, 2019). Readers unfamiliar with fluid dynamics are referred to Shapiro (1961) and Vogel (1994).…”