Muscle growth in Nile tilapia ( Oreochromis niloticus): histochemical, ultrastructural and morphometric study

Abstract

Muscle growth in Nile tilapia ( Oreochromis niloticus) was studied focusing on histochemical, ultrastructural, and morphometric characteristics of muscle fibers. Based on body length (cm), we studied four groups: G1=1.36±0.09, G2=3.38±0.44, G3=8.90±1.47, and G4=28.30±3.29 (mean±S.D.). All groups showed intense reaction to NADH-TR in subdermal fibers and weak or no reaction in deep layer fibers. In G3 and G4, an intermediate layer was also observed with fibers presenting weak reaction; in G4, groups of fibers with intense reaction were observed in the subdermal region. The myosin ATPase (m-ATPase) activities were acid-stable and alkali-labile in subdermal fibers; most deep layer fibers were alkali-stable and acid-labile. Intermediate fibers were acid-labile and alkali-stable. Two fiber populations were observed near deep muscle layer: one large presenting weak acid- and alkali-stable and the other small alkali-stable. During growth, muscle fiber hypertrophy was more evident in intermediate and white fibers for G3 and G4. However, in these groups, the presence of fiber diameters ≤21 μm suggested that there is still substantial fiber recruitment, confirmed by ultrastructural study, but hypertrophy is the main mechanism contributing to increase in muscular mass.