My doctoral dissertation research focused on locomotor mechanisms in fishes. Specifically, I chose to examine pectoral fin (labriform) swimming, a mode of locomotion widespread among fishes and involved in an array of ecologically important behaviors yet largely unstudied at the time from a functional perspective. Surfperches (Figure 1) utilize labriform swimming throughout their development and in varied habitats, thus offering a model system for examining the influence of scale and ecology on swimming performance (see references 1 and 2 below). With increasing speed, surfperches exhibit a gait transition from purely pectoral fin swimming to combined pectoral and caudal fin (tail) propulsion. At the pectoral-caudal gait transition speed (Up-c), fish varying 100-fold in body mass exhibit kinematically similar fin movements with size-independent propulsive efficiency. On this basis, I proposed that the speed elicits 'physiologically equivalent' levels of exercise in swimmers of different size and is therefore valid for allometric comparisons (ref. 3). Stride frequency at gait transition in both fishes and terrestrial vertebrates shows remarkably similar scaling, an observation that may be explained by an underlying similarity in the allometry of maximal muscle shortening velocity.

		View Quicktime movies of surfperch locomotion
Figure 1. The striped surfperch swimming by means of pectoral fin propulsion.

When expressed in terms of body lengths traveled per second according to the traditional standardization, the equivalent speed Up-c varies dramatically among fishes of different size and ecological association. It follows, therefore, that individual length-specific speeds, despite their long-standing use, do not represent comparable levels of activity from different fishes. I developed a new, alternative approach that successfully controls for variation in animal activity level in which speed is standardized to a percentage of Up-c, the performance limit for pectoral fin swimming. I applied this method in a study of the neuromuscular control of pectoral fin movements in open-water and reef-dwelling surfperches (ref. 4), representatives of the two ecologically distinct subfamilies of the Embiotocidae (Figure 2). By examining taxa at the extremes of both phylogenetic and ecological divergence in the family, I was able to interpret mechanistic similarities (e.g. in temporal pattern of fin movement and intensity of muscle recruitment) as features primitive for embiotocids.

Figure 2. Intrarelationships of the surfperches highlighting species used in comparative studies of pectoral fin locomotion.

My current postdoctoral research extends my previous biomechanical work in a complementary direction. In collaboration with Dr. George Lauder of Harvard University, I am examining the fluid dynamics of fin-based propulsion in freely swimming fishes. By focusing on the hydrodynamic interface between the organism and its physical environment--the locus of fluid force production--it is possible to gain new insights into how aquatic animals accomplish everyday locomotor tasks. I have adopted a modern flow visualization technique (Digital Particle Image Velocimetry, DPIV) from the field of fluid mechanics, which allows one to characterize the three-dimensional structure of the wake shed by moving fins (Figure 3), and thereby gain information that has been lacking in past analyses: empirical, quantitative data on swimming force. A key advantage of this experimental approach over previous analyses is that it does not involve simplifying assumptions about flow properties or fin motion (as do theoretical models). In the course of my postdoctoral research, I have provided the first empirical demonstration of a hydrodynamic force balance on a steadily swimming fish (ref. 5), developed a mechanistic explanation for interspecific differences in swimming speed through a comparative analysis of wake dynamics (ref. 6), and performed a quantitative study of unsteady turning maneuvers--locomotor behaviors revealing the functional versatility of the teleost pectoral fin (ref. 7). Most recently I have used DPIV to assign locomotor function to the dorsal fin of teleost fishes, and to explore constructive wake interactions among multiple median fins that may enhance thrust production (ref. 8).

Figure 3. Schematic three-dimensional reconstructions of the pectoral fin wake of bluegill sunfish swimming at two speeds. Left, 1.0 body length per second. Right, 1.5 body length per second. Red arrows indicate direction of fluid flow measured in planar wake transections.

View Quicktime movies of the pectoral fin wake of freely swimming sunfish

 Relevant Publications (red links: full-text PDF; blue links: abstract only)

1. Drucker, E. G. and J. S. Jensen. 1996. Pectoral fin locomotion in the striped surfperch. I. Kinematic effects of swimming speed and body size. Journal of Experimental Biology 199: 2235-2242.

2. Drucker, E. G. and J. S. Jensen. 1996. Pectoral fin locomotion in the striped surfperch. II. Scaling swimming kinematics and performance at a gait transition. Journal of Experimental Biology 199: 2243-2252.

3. Drucker, E. G. 1996. The use of gait transition speed in comparative studies of fish locomotion. American Zoologist 36: 555-566.

4. Drucker, E. G. and J. S. Jensen. 1997. Kinematic and electromyographic analysis of steady pectoral fin swimming in the surfperches. Journal of Experimental Biology 200: 1709-1723.

5. Drucker, E. G. and G. V. Lauder. 1999. Locomotor forces on a swimming fish: three-dimensional vortex wake dynamics quantified using digital particle image velocimetry. Journal of Experimental Biology 202: 2393-2412. [Cover illustration / (PDF)]

6. Drucker, E. G. and G. V. Lauder. 2000. A hydrodynamic analysis of fish swimming speed: wake structure and locomotor force in slow and fast labriform swimmers. Journal of Experimental Biology 203: 2379-2393.

7. Drucker, E. G. and G. V. Lauder. 2001. Wake dynamics and fluid forces of turning maneuvers in sunfish. Journal of Experimental Biology 204: 431-442.

8. Drucker, E. G. and G. V. Lauder. 2001. Locomotor function of the dorsal fin in teleost fishes: experimental analysis of wake forces in sunfish. Journal of Experimental Biology 204: 2943-2958. [Cover illustration / (PDF)] [JEB News and Views article]

Complete publication list