The Jaw Mechanism During Growth of a Generalized Haplochromis Species: H. Elegans Trewavas 1933 (Pisces, Cichlidae)

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Abstract
This paper deals with the jaw mechanism of Haplochromis elegans, a generalized1 Haplochromis2 species. The central issues are the kinematics and statics of the mechanism and the way these are influenced by its proportions. These proportions change during growth and differ in related species. A mathematical computer model is formulated to deal with the kinematics and the statics of the mechanism. A calculation procedure is developed to determine the importance of the position of anatomical points in the mechanism for force-transmission during biting. It is also possible to change the position of all relevant anatomical points gradually and thereby improve the whole mechanism for the function of biting. In this way a prediction is made about the proportions expected in a powerful biting haplochromine species such as H. nigricans. The predictions made are correct in six of the seven specialized proportions of H. nigricans. A simplified kinematical model is presented which demonstrates the essence of protrusion in cichlid fishes and in many other acanthopterygian fishes. The differences in proportions of an adult and a first free-swimming stage of H. elegans are evaluated with the computer model. It appears that some proportions are more favourable for biting in the young stage, others are unfavourable due to the relative size of the eye.

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