MUSCLE GROWTH IN RESPONSE TO CHANGING DEMANDS OF FUNCTIONS IN THE TELEOST SPARUS-AURATA (L.) DURING DEVELOPMENT FROM HATCHING TO JUVENILE

Growth of laterarl muscle in the teleost fish Sparus aurata (L.) was e xamined from hatching to juvenile by a basic morphofunctional approach that takes into account structural and ecophysiological aspects and c ombines in vivo observations and LM and TEM microscopic analysis. As s hown in most teleost fishes, muscle growth proceeds by a double mechan ism of hyperplasia and hypertrophy that contribute differentially to t he overall development of the lateral muscle, giving rise in each myom ere to a typical pattern of structurally and functionally different fi bre types (slow-red and fast-white fibres, plus pink intermediate fibr es) in a nerve-dependent process. During larval life the muscle growth takes place mainly due to hyperplastic growth at the level of specifi c proliferative zones of the myomeres, from which slow, pink and white muscle fibres are derived. In those species that reach a large adult size a new typical hyperplastic process disseminated throughout the fa st white muscle layer takes place during post-larval life. In contrast , hypertrophic growth occurs in all stages, but is the dominant mechan ism of muscle growth only in juvenile and adult. The suitable recruitm ent of the different fibre types enables the fish to optimize its perf ormances according to specific functional and metabolic requirements r elated to the swimming behaviour and hydrodynamic regimes. The differe nt mechanisms of growth are here analysed in their detailed structural and ultrastructural aspects in order to interpret their adaptive sign ificance in the light of the fish life cycle, with particular referenc e to locomotion and feeding behaviour.