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First published online May 24, 2005
Journal of Experimental Biology 208, 2103-2114 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01603

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Scaling of suction-feeding kinematics and dynamics in the African catfish, Clarias gariepinus

Sam Van Wassenbergh^*, Peter Aerts and Anthony Herrel

Department of Biology, University of Antwerp (U.A.), Universiteitsplein 1, B-2610 Antwerpen, Belgium

View larger version (48K): [in a new window]   Fig. 1. Selected video frames from a representative prey capture sequence for one individual of Clarias gariepinus (30.2 cm total length) feeding on an attached piece of cod. Lateral view (top frames) and ventral view (bottom frames) are recorded simultaneously.

View larger version (37K): [in a new window]   Fig. 2. Anatomical landmarks digitized (black points) with the calculated kinematic variables (arrows) on the lateral (A) and ventral (B) high-speed video images of Clarias gariepinus. The landmarks are: 1, middle of the eye; 2, upper jaw tip, interior side; 3, lower jaw tip, interior side; 4, tip of the hyoid; 5, most ventrally positioned point of the branchiostegal membrane; 6, rostral tip of the skull roof; 7, caudal tip of the skull roof; 8, anterior tip of the caudal fin; 9, hyoid symphysis; 10,11, most caudally discernible points on the hyoid bars; 12,14, base of pectoral spine; 13,15, lateral tip of the branchiostegal membrane. The measured linear variables are: gape distance (a), hyoid depression (b), branchiostegal depression (c) and lateral branchiostegal expansion (f, average between left and right). The angular variables are: neurocranial elevation (d) and lateral hyoid abduction (e). The red lines represent the coordinate system moving with the head of the catfish.

View larger version (39K): [in a new window]   Fig. 3. Three-dimensional representation of the model used for calculation of power requirement of suction feeding in C. gariepinus. The model consists of 201 serially arranged hollow elliptical cylinders (left). Each cylinder consists of an external ellipse bordering the fish's head and an internal ellipse bordering the buccal cavity (right). Movement of the centres of mass (red and green dots) of 40 subdivisions of the modelled head volume (red and green segments) with respect to a fixed frame of reference (XYZ) was computed during the expansive phase for each cylinder. The 16 segments that approximately correspond to the neurocranium are indicated in red. Note that depth, d, is exaggerated for clarity. See text for further explanation and definition of symbols.

View larger version (46K): [in a new window]   Fig. 4. Example of buccal pressures calculated for a prey capture sequence of a 35.2 mm cranial length C. gariepinus. Pressures for three positions inside the buccal cavity (circles), as well as mouth opening (open triangles) and hyoid depression (filled triangles) versus time are given. Note that these calculations are only valid when the opercular and branchiostegal valves are closed (grey background) (i.e. approximately until maximal gape is reached).

View larger version (30K): [in a new window]   Fig. 5. Log-log plots of maximal linear displacement (A,B), velocity (C,D) and acceleration (E,F) versus cranial length, for mouth opening (A,C,E) and hyoid depression (B,D,F).

View larger version (31K): [in a new window]   Fig. 6. Log-log plots of maximal angular displacement (A,B) and velocity (C,D) versus cranial length for neurocranial elevation (A,C) and lateral hyoid abduction (B,D).

View larger version (13K): [in a new window]   Fig. 7. Log-log plots of maximal peak negative buccal pressure (A) and maximal average buccal pressure (B) versus cranial length. These buccal pressures are averaged over the entire buccal cavity (from mouth aperture to pectoral fin) and were calculated with hydrodynamic models (Drost and van den Boogaert, 1986; Muller et al., 1982). Note that no significant changes were found for these pressures in relation to cranial size.

View larger version (16K): [in a new window]   Fig. 8. Log-log plots of peak muscle-mass-specific power requirement (A) and average muscle-mass-specific power requirement (B) versus cranial length, as calculated using the model presented in this paper. Note that peak-mass-specific power decreases significantly with increasing cranial size.

View larger version (17K): [in a new window]   Fig. 9. Relative contribution of forces in the direction of motion as a result of buccal pressure (Fpressure), acceleration of mass and added mass (Finertia) and hydrodynamic drag (Fdrag) to the total force, as estimated by dynamic modelling. Note that forces due to friction between head parts and from deformation of tissues are not included in the model. No significant changes with size are found.

View larger version (16K): [in a new window]   Fig. 10. Log-log plots of total work (A) and muscle-mass-specific work (B) from the start of mouth opening until maximum gape versus cranial length, as calculated using the model presented in this paper. Note that, while total work increases significantly with increasing cranial size (A), the muscle-mass-specific work output decreases significantly with increasing cranial size (B).