FEEDING PERFORMANCE AND MUSCULAR CONSTRAINTS IN FISH

Analysis of the feeding kinematics of Astatotilapia (a small cichlid f ish) suggests the presence of peripheral feedback modulation of the mo tor pattern, allowing the act of suction to be abbreviated. In this wa y, the effort spent in suction is minimized. The biological significan ce of the development of such a modulating feedback system is not imme diately obvious from a 'classical ecological' point of view. It is pos tulated that the muscular metabolism itself might constrain the short, transient and strenuous motor output typical of suction feeding. Thus , reducing the suction effort makes sense when successive strenuous he ad-part movements are immediately required for additional suction, buc cal transport or spitting. This hypothesis was tested by in vivo elect rical stimulation of muscles important in feeding: the epaxials, which lift the skull and expand the buccal cavity. Reliable stimulation var iables for the epaxial muscles were determined from preliminary stimul ation experiments and from electromyographic recordings of these muscl es in a specimen feeding on crickets. Stimulation trains of variable d uration (<150 ms) were applied in series of five trains. The intervals between trains were variable as well (<1 s). The mechanical output wa s measured by means of an accelerometer, a force transducer or a magne toresistive displacement transducer. In the latter case, the time cour se of the mechanical output could be recorded and analysed. The hypoth esis predicts a decrease in the muscular output with increasing effort (long trains) and fast repetition (short intervals). The experimental results show the expected decline in mechanical output from one stimu lation train to the next when longer stimulation bursts are imposed in quick succession. Statistical analyses (multiple regression) showed t hat train length, train rate and train number contribute significantly to the observed variation in mechanical output, supporting the hypoth esis. Explanations for the phenomena are discussed.