Red muscle development of gilthead sea bream Sparus aurata (L.): Structural and ultrastructural morphometry

The transverse red and white muscle area, the superficial red muscle fibres area and their percentages of mitochondria (%(mit)), myofibrils (%(myof)) and sarcoplasm (%(sarc)) were determined in the Mediterranean teleost gilth ead sea bream, Sparus aurata (L.). Fish aged from hatching to 78 days were studied. The proportional growth of the red and white muscles was higher fo r the red muscle in the first half of the larval stage (1-35 days). Then th e opposite relationship was observed. The hypertrophic growth of the superf icial muscle fibres was continuous except in the first week after hatching. The percentage of mitochondria and percentage of myofibrils showed a signi ficant change just after the half of the larval stage. Whereas the %(mit) o f the superficial muscle fibres was higher than %(myof) from the first week after hatching to 35 days (average 66.64 %), then the %(mit) decreased sig nificantly and at 73-78 days both parameters were close to an average value of 50 %. The meaning of these morphological changes is discussed in relati on to the functional role of the red muscle of larvae and the onset of the gills respiration.