Proportions of the jaw mechanism of cichlid fishes changes and their meaning

The jaw mechanism of cichlid fishes is an intricate apparatus with complex force transmission from muscles to environment. The proportions of this apparatus change considerably during growth mainly due to scale effects. In adult fishes, the proportions differ, corresponding with the type of preferred food. In such a complex mechanism, it is very hard to gain insight into the functional meaning of the differences in proportions, unless a biomechanical model is constructed, describing kinematics and force equilibria of the apparatus.Such a model has been constructed and by means of perturbation analysis anatomical points could be selected of which the positions are very important for the function of biting. These hot spots need only small displacements in order to obtain an increase in biting force. By means of a newly developed mathematical technique, it was possible to move the anatomical points in very small steps towards more favourable positions for the function of biting.In this way, an improved version of an existing not very powerful biting insect feeding species, Haplochromis elegans, was calculated. This calculated version resembles a more powerful biting species Haplochromis nigricans very closely. Also, the functional meaning of the proportional changes during growth of the insect feeding Haplochromis elegans could be evaluated. In both cases compromises could be indicated where functional demands are in conflict with each other on the level of the anatomical design of the jaw mechanism.