Abstract
The ears of fishes are remarkable sensors for the small acoustic disturbances associated with
underwater sound. For example, each ear of the Atlantic cod (Gadus morhua) has three dense
bony bodies (otoliths) surrounded by fluid and tissue, and detects sounds at frequencies from 30
to 500 Hz. Atlantic cod have also been shown to localize sounds. However, how their ears
perform these functions is not fully understood. Steady streaming, or time-independent, flows
near a 350% scale model Atlantic cod otolith immersed in a viscous fluid were studied to
determine if these fluid flows contain acoustically relevant information that could be detected by
the ear’s sensory hair cells. The otolith was oscillated sinusoidally at various orientations at
frequencies of 8–24 Hz, corresponding to an actual frequency range of 280–830 Hz. Phaselocked
particle pathline visualizations of the resulting flows give velocity, vorticity, and rate of
strain fields over a single plane of this mainly two-dimensional flow. Although the streaming
flows contain acoustically relevant information, the displacements due to these flows are likely
too small to explain Atlantic cod hearing abilities near threshold. The results, however, may
suggest a possible mechanism for detection of ultrasound in some fish species.
