Date of Award

Spring 5-1-2025

Document Type

Thesis

Degree Name

Master of Science in Coastal Marine and Wetland Studies

Department

Coastal and Marine Systems Science

College

College of Science

First Advisor

Roi Gurka

Second Advisor

Erin E. Hackett

Third Advisor

Derek Crane

Abstract

Suction-feeding is a common method for capturing prey by aquatic organisms and contributed to the diversification of fishes by enabling them to consume a wide range of prey. Suction-feeding is a complex fish-fluid interaction governed by various hydrodynamic forces: inertia, unsteady, viscous, and pressure gradients. These forces are described by the coupling between the flow physics equations (Navier-Stokes) and the dynamic behavior of the fish (motion and forces). However, the distribution of the pressure field that drives this process, and the extent to which suction-feeding is three-dimensional, remain underexplored. I estimated the pressure within the flow field surrounding the mouth of a Bluegill sunfish (Lepomis macrochirus) during suction-feeding utilizing particle image velocimetry (PIV). Particle tracking velocimetry (PTV) was also used to measure the 3D velocity fields in a volume surrounding the mouth of a Bluegill. High-speed imaging was used for measurements of fish kinematics (duration and amplitude). The pressure field was estimated from the PIV velocity measurements through the Poisson equation. The boundary conditions for the pressure field were determined from the integral momentum equation, separately, for three phases of the suction-feeding cycle. I explored suction- feeding by quantifying the pressure field that drives the flow towards the buccal cavity, where the magnitude and location of a high-pressure zone varies throughout the feeding cycle causing significant variations of the spatial pressure distribution. Measurements of the 3D flow field enables direct measurement of all the hydrodynamic forces governing flow, which provides insight into the coupling effects between viscous, inertia and pressure gradient forces acting during the phases of suction-feeding. In particular, the 3D flow measurements enable a direct estimate of the pressure gradient terms in all three directions, which is not possible with 2D measurements utilizing, for example, PIV. These interactions are important because they govern the success rate and energy expenditure during the suction-feeding process. PIV analysis showed clear variation in pressure fields across phases, with regions of high pressure forming during mouth expansion, supporting the role of unsteady pressure gradients in prey capture. PTV data revealed that the three velocity components (u, v, w) had comparable magnitudes, indicating strong three-dimensional flow. These results provide novel insight into the pressure-driven mechanisms of suction-feeding and highlight the importance of 3D flow structure in prey acquisition.

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