Analyses of Respiration and Feeding Movements of the Three-Spined Stickleback, Gasterosteus Aculeatus L

Abstract

Respiratory, eating, and spitting movements of Gasterosteus aculeatus L. were analysed. An apparatus for direct X-ray cinematography and an injection device to mark distinct places facilitated accurate determination of the mutual positions of skeletal elements during respiratory movements. The analysed respiratory movements show large variations, but share a definite similar pattern characterized as follows: a. Opening and closing of the mouth precede abduction and adduction of the suspensorium, respectively. b. The depression and elevation of the tongue and the laterally and medially directed movements of the hyoid run synchronously with suspensorial abduction and adduction, respectively. c. The opercular abduction is larger than the suspensorial abduction, and the opercular bones reach their ultimate positions some time later. Opercular dilatation is superimposed on suspensorial abduction of the operculum. d. The interhyal does not swing posteriorly synchronously with depression of the lower jaw. This points to an inactive musculus sternohyoideus-hyoid-interopercularmandible mechanism for opening of the mouth. e. The interoperculum and the ventral part of the gill cover swing posteriorly synchronously with the depression of the lower jaw. This points to an active levator operculi-operculum apparatus-mandible mechanism for opening of the mouth. f. Minor differences between the courses of expansion and of narrowing of the cavities indicate that, apart from muscle forces also elastic-tissue forces and resistance of the water determine these courses in addition to the way in which the skeletal elemens are connected in a kinematic chain. g. Successive large ventrally and dorsally directed shifts of the tongue will in turn enlarge the buccal cavity at the cost of the branchial cavities, and the reverse also holds. Motion pictures of eating and spitting movements were made, the lateral and ventral views with a mirror placed at a 45° angle. One scene shows snapping and spitting movements during which a worm is drawn into and ejected from the mouth within a second. A snap is characterized by an explosive expansion of the buccal and branchial cavities during opening of the mouth, suspensorial abduction, hyoid depression, and opercular abduction. The mouth reaches its ultimate open position and then immediately shuts rapidly to enclose the prey. Suspensorial and opercular adduction takes more time and thus stops later. The speed with which the mouth is opened varies strongly, but is higher the larger the prey. A spit is characterized by gradual expansion of the branchial cavities by strong abduction of the gill covers, followed successively by suspensorial abduction and opening of the mouth. Opercular and suspensorial adduction start while the mouth is still opening and staying open for some time. The adduction ends during the relatively fast closure of the mouth. The prey enters the mouth during the explosive expansion phase of a snap and leaves the mouth during opercular and suspensorial adduction when the fish opens its mouth. The activities of the main muscles are predicted and the relative value of these predictions is discussed.