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Feeding mechanisms in carp: crossflow filtration, palatal protrusions and flow reversals

W. Todd Callan and S. Laurie Sanderson^*

Department of Biology, College of William and Mary, Williamsburg, VA 23187, USA

View larger version (25K): [in a new window]   Fig. 1. Schematic of the carp oropharyngeal cavity, indicating endoscope insertion site. The roof of the oropharynx is illustrated on the left, with the palatal organ (po) shown in coarse stippling and the region of po observed through the endoscope in fine stippling. The floor of the oropharynx is illustrated on the right, with ceratobranchials I—IV (cb I—IV) shown as black bars. The location of the gill rakers is shown by the gray shading. The hatched region of the gill arches was observable through the endoscope. Modified from Sibbing et al. (1986).

View larger version (95K): [in a new window]   Fig. 2. Endoscopic video image showing rows of gill rakers on ceratobranchials I—IV (cb I—IV). The anterior of the fish is to the right. The palatal organ (po) on the roof of the anterior pharynx is located at the top of the image. The portion of cb III that is in the field of view is approximately 1.5 cm in length.

View larger version (44K): [in a new window]   Fig. 3. Endoscopic images illustrating a typical sequence observed during feeding on slurry particles off a gravel substrate (125 frames s-1; duration of sequence 104 ms; frames 1, 6 and 13 shown). The anterior of the fish is to the left. Rows of gill rakers on ceratobranchials I—IV (cb I—IV) are visible, as well as the palatal organ (po). (A) A rock (r) is pressed down and pinned by the palatal organ across cb IV. (B) A slurry particle (p) and (C) a brine shrimp cyst (p) travel posteriorly past the rock and do not come into contact with any pharyngeal surface while in the field of view. Movie available online (movie: fig3.mov).

View larger version (84K): [in a new window]   Fig. 4. Endoscopic images illustrating a protrusion (pr) of the palatal organ during feeding on slurry off a sand substrate (500 frames s-1; duration of sequence 64 ms; frames 1, 5, 8, 9, 10 and 12 shown). The anterior of the fish is to the right. Ceratobranchials I and II (cb I; cb II) are visible. (A) A protrusion of tissue from the palatal organ is projecting towards cb II. (B) The protrusion has come into contact with cb II. (C) A sand grain has entered the field of view on the left side of the protrusion during a flow reversal. (D) The sand grain passes lateral to the protrusion. (E) The protrusion begins to move dorsally and lifts from cb II while the water is still moving anteriorly during the flow reversal. (F) The palatal organ is returning to its original shape. Movie available online (movie: fig4.mov).

View larger version (102K): [in a new window]   Fig. 5. Endoscopic images illustrating a typical sequence observed during feeding on pellets off a gravel substrate (30 frames s-1; duration of sequence 267 ms). The anterior of the fish is to the right. The palatal organ (po) is visible above rows of gill rakers on ceratobranchials I—III (cb I—III). (A) A pellet (pe) is observed entering the field of view and being pinned across cb III by an overall height reduction of the pharyngeal slit. (B) A rock (r1) enters the field of view, followed by (C) a second rock (r2) and (D) a third rock (r3). (E) r2 is pinned across cb II by an overall height reduction of the pharyngeal slit, preventing further posterior movement. (F) r2 is released by the palatal organ. (G) r3 has moved anteriorly out of the field of view during a spit, and r2 moves further anteriorly. (H) r2 almost completely leaves the field of view in an anterior direction. r1 is visible again behind r2. (I) r2 is spat anteriorly out of the field of view while the pellet and r1 remain pinned across cb III. r1 exited anteriorly from the field of view in the subsequent frame, while the pellet was retained by a palatal protrusion. Movie available online (movie: fig5.mov).