本篇利用半厚片及形態分析以探討嘉鱲魚仔魚時期肌肉的發育情形。仔魚孵化時,卵黃囊(yolk sac)的體積佔身體的大部分;而軀幹肌由單層的上表層肌肉(superficialmuscle layer)及內層肌肉(inner muscle mass)所組成。孵化後4天,魚的身體由彎曲變直,且內層的肌母細胞逐漸分化,包括上層肌肉及內層肌肉都有肌纖維(fiber)的出現,且可以看到許多的橫紋(cross-striations)。而在6天時,卵黃囊消耗完畢,肌肉的主要功能轉變為捕捉獵物或逃避敵害。從第3天到第9天,肌肉的面積及肌纖維的大小都沒有很明顯的變化;但在第9到第12天時,面積及大小都有明顯的增加。因此,嘉鱲魚仔魚時期的肌肉成長模式,早期(0-9天)主要是藉由增生(hyperplasia),而逐漸轉變為增大(hyper-trophy)為主(肌纖維的大小在第9到12天有顯著的增加)。
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.