Species Composition and Seasonal Occurrence of Mullets(Pisces,Mugilidae)in the Tanshui Estuary Northwest Taiwan

The ontogenetic development of the trunk muscle in the early stage of red sea bream(Pagrus major)was studied by semi-thin microscopic work and morphometric analysis.Larval fish hatched out with a large yolk sac,and with small mass of myotomes.Theirmyotomes were made up of a oingle superficial muscle layer,and the inner muscle mass.Four-day-old larvae had the straightened body axis and their inner core of myoblastsstarted differentiation.The trunk muscle,including inner muscle zone and some superficialmuscle layer,differentiated to”fiber”with lots of significant cross-striations inside.In six-day-old larvae,yolk sacs were completely absorbed,and their major muscle function translatesinto the movement for capturing preys and avoiding predators.During the 3(superscript rd)and the9(superscript th)days old,the muscle areas and the fiber diameters did not change remarkably.Incontrast,both areas and diameters increased significantly when fish grew from 9-day-oldto 12-day-old.Therefore,the ontogenetic change of fiber diameters demonstrated themajority of larval growth in red sea bream depended on hyperplasia in the earlier stages(0-9 days)and then hypertrophy(fiber diameters increased significantly from 9-to 12-day-old)participated the growth function in the latter stages.