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First published online May 24, 2005
Journal of Experimental Biology 208, 2091-2102 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01604

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A functional morphological approach to the scaling of the feeding system in the African catfish, Clarias gariepinus

Anthony Herrel^1,*, Sam Van Wassenbergh¹, Sarah Wouters¹, Dominique Adriaens² and Peter Aerts¹

¹ Dept Biology, University of Antwerp, Universiteitsplein 1, B-2610 Antwerpen, Belgium
² Institute of Zoology, University of Ghent, K.L. Ledeganckstraat 35, B-9000, Ghent, Belgium

View larger version (33K): [in a new window]   Fig. 1. Linear dimensions determined on the skeletal elements of the feeding apparatus in Clarias gariepinus. (A) Dorsal view of the lower jaw, illustrating the measurement of lower jaw length and angle. (B) Lateral view of the lower jaw, illustrating the measurement of lower jaw length, coronoid height (ch), the in-lever for jaw closing (close) and the in-lever for jaw opening (open). (C) Ventral view of the hyoid, illustrating the measurement of hyoid length and angle. (D) Lateral view of the hyoid, illustrating the measurement of hyoid length and depth. (E) Dorsal view on the cleithrum, illustrating the measurement of cleithrum symhysis length (s.i.) and cleithrum angle. (F) Medial view of the operculum, illustrating the measurement of operculum length. Pictures are not to scale.

View larger version (43K): [in a new window]   Fig. 2. (A) Lateral view of the head of a juvenile Clarias gariepinus. Indicated are the muscles and bony elements used in this study. Note that the m. A2A3' has been partially cut to expose the underlying m. levator arcus palatini and the m. A3''. (B) Ventral view on the hyoid musculature of the same juvenile Clarias gariepinus. Note that the bottom of the fish has been dissected to expose the lower jaw, hyoid, cleithrum and m. sternohyoideus. Scale bar, 5 mm.

View larger version (17K): [in a new window]   Fig. 3. Graphical representation of the scaling of external head dimensions versus fish standard length in C. gariepinus. Both head length (A) and head width (B) scale with significant negative allometry (see Table 1). The broken line represents the expected slope of 1 under a model of geometric similarity.

View larger version (39K): [in a new window]   Fig. 4. Graphical representation of the scaling of skeletal dimensions of the cleithrum in Clarias gariepinus. The mass (A) and length (B) of the cleithrum both scale with significant positive allometry (slope different from 3 and 1, respectively; see Table 2). The angle between the two halves of the cleithrum (C) scales with marginal but significant negative allometry (Table 2). The broken lines represent the expected slope under a model of geometric similarity (mass=3, length=1, angle=0). (D) A series of representative cleithra, illustrating the difference in shape in different individuals. The different filled symbols on the graphs correspond to the respective cleithra illustrated. Scale bar, 50 mm.

View larger version (15K): [in a new window]   Fig. 5. Graphical representation of the scaling of a jaw closing muscle in Clarias gariepinus. Although the mass of the muscle (A) scales with the expected slope of 3, the fibre length (B) scales with significant negative allometry (Table 3). Thus, the physiological cross-section (C) scales with significant positive allometry. The broken lines represent the expected slope under a model of geometric similarity (mass=3, length=1, cross-section=2).

View larger version (14K): [in a new window]   Fig. 6. Graphical representation of the scaling of an expansive muscle in Clarias gariepinus. The mass (A) scales with significant positive allometry. Fibre lengths (B) increase with fish cranial length in accordance with the predictions of geometric similarity (slope not different from 1; see Table 3). The physiological cross-sectional area (C) also increases with significant positive allometry. The broken lines represent the expected slope under a model of geometric similarity (mass=3, length=1, cross-section=2). SH = m. sternohyoideus.

View larger version (23K): [in a new window]   Fig. 7. Graphical representation of the scaling of bite force (A,B) and jaw closing velocity (C,D) versus cranial length in C. gariepinus. Bite force increases with cranial length with a slope of 3 (A), and jaw closing velocity decreases with cranial length with a slope of -0.66 (C). Upon detailed inspection of the graphs, a break point appears to be present at a cranial length of 65 mm (B,D). Analysis of the scaling patterns for the two groups separately indicates a rapid increase in bite force (B; slope=3.92) but no change in jaw closing velocity (note that the trend line in D to the left of the break point is not significantly different from 0) for fish under 65 mm cranial length. Above 65 mm cranial length, bite force increases with a slope of 2.58 and jaw closing velocity decreases with a slope of -0.79.