PAUL*, J. C.; HALE, M. E. ; Univ. of Chicago; Univ. of Chicago: Locomotor behavior of zebrafish with aberrant myomere morphology

Fish generate axial bending through contractions of the myomeres, serially repeated lateral muscles in the trunk and tail. Myomeres have an elaborate three-dimensional shape and fiber organization. In this study, we examine kinematics of a larval zebrafish muscle mutant in order to investigate the roles of myomeric muscle fiber organization in axial locomotion. Muscle mutants provide an attractive system for such work because myomeres and myosepta may be altered while the spinal cord organization and innervation of the axial muscle remains intact. In addition, transgenic zebrafish lines in which green fluorescent protein is expressed in muscle fibers allow us to ready visualize three-dimensional muscle morphology in the intact, live animal thus preventing distortion associated with fixation and sectioning. For this study, we examined the fused somites mutant (fss) (van Eaden, et al.(1996) Development 123:153-164) crossed with an a-actin transgenic (Higashijima et al.(1997) Dev Biol 192:289-299). To quantify muscle fiber organization, the morphology of muscle fibers in the epaxial muscle was measured and compared to that of wild type fish. Myomeres of the mutant had irregular morphology and incomplete myoseptal boundaries. Fibers were significantly longer than those of wild type fish, often extending across several segments. In addition, the inclination of fibers relative to the sagittal and transverse planes was lower than in wild type fish. Comparison of fast-start performance between mutant and wild type fish showed significant decreases in aspects of performance, including angular displacement and angular velocity, in the mutant, although other parameters, including overall body bending, did not differ. This study shows that fish can perform startle behavior and swimming with severely disrupted myomere structure; however, aspects of performance may be lowered.