Development of the Lateral Muscle in the Japanese Sardine Sardinops melanostictus

Abstract

Histochemical characteristics of lateral muscle fiber types in the Japanese sardine Sardinops melanostictus were confirmed and their developmental process investigated. In 102 and 106 mm young specimens in standard length (SL), four muscle fiber types, i.e., red, pink, white, and tonic-like fibers were recognized. Pink fibers mainly occurred in the anterior trunk region. Two types of tonic-like fibers were recognized around the red triangular wedge along the horizontal septum. Newly-hatched larvae (free embryos) had a single layer of superficial fibers containing a few myofibrils and inner white fibers. Histochemical reactions for NADHD and lipid in the superficial fibers gradually increased and became strong enough to be classified as red fibers by the first-feeding stage. Beyond about 20 mm SL, stratification of the red fibers, differentiation of the tonic-like fibers, and mosaic appearance of the white fibers occurred. By 30 mm SL, pink fibers and two types of tonic-like fibers were differentiated. The structure of the lateral muscle in a 37 mm SL juvenile was complete and did not differ from those of young specimens, 102 and 106 mm SL.