Gill arch movements and the function of the dorsal gill arch muscles in the carp.

The activity coordination of the dorsal gill arch muscles in a teleost, the carp, is described and the effect of their contraction in combination with the respiratory pump movements is analysed. Based on their origin and insertion the dorsal branchial arch muscles can be divided into three groups: the external branchial arch levators, connecting the branchial arches to the neurocranium, the internal branchial arch levators, connecting the pharyngobranchials to the neurocranium and the dorsal oblique muscles, interconnecting the branchial arches and pharyngobranchials. Functionally, however, there are only two categories with the following properties. The first, which consists of the external branchial arch levators alone, is active during every respiratory cycle, including the cough. These muscles expand the branchial basket through gill arch abduction and, in combination with hyomandibular pumping movements, lower the floor of the buccal cavity. The results of these combined movements are: The gill arches remain evenly distributed within the expanding branchial cavities during inspiration, so that continuity of the gill curtain is maintained. Water flow resistance is reduced also. The volume of water flowing into the buccal cavity during inspiration is increased. The second category, comprising the internal branchial arch levators and the dorsal oblique muscles, contracts only during the cough and else is completely inactive. Contraction of these muscles reinforces the dorsal suspension of the gill arches by firmly anchoring the pharyngobranchials and epibranchials to the base of the skull. In this way strong, caudally directed forces which develop during the intermediate expansion of the cough can be prevented from dislocating the branchial basket.