Comparison On Fast- Twitch And Slow-twitch Skeletal Muscle And Muscle Fibers Development At Early Stages Of Mandarin Fish Siniperca Chuatsi

Skeletal muscle is the main contributor to body weight in most fish, it is probable that the size of a fish is limited by the growth of this tissue. Muscle fibers and their molecular composition is the important base for evaluation on fish meat quality. To fully understand the characterization of fast-twitch and slow-twitch muscle of mandarin fish Siniperca chuatsi and the characteristics of skeletal muscle fibers development at the early stage of mandarin fish, some researches have been done. Histological characters of two different skeletal muscles (fast-twitch and slow-twitch muscle) were analyzed by paraffin sections, these two muscle fibres had different shapes and diameter(s50.0-91.5μm,12.2-44.2μm). Protein composition of fast muscle and slow muscle were compared according to the number of protein bands and their mobility separated by polyacrylamide gel electrophoresis (SDS-PAGE), some specific bands existed in 50-60ku and 10-15ku. The subfragment-1(S1) cDNA of the fast and slow muscle moysin heavy chain were cloned and sequenced by PCR method, the S1 sequences of fast and slow muscle were 2523bp and 2520bp, which encoded 841and 840 amino acids, respectively. They shared 87.6% identities in amino acid sequence, of which loop-1 and loop-2 regions were highly variable. These results showed that fast muscle and slow muscle had significantly differences at histological, protein composition and molecular levels, which suggested their different motion functions. Paraffin sections of the first dorsal myomere of skeletal muscle at 1-41 days after hatching were carried out; fiber numbers and total fibre area were measured to describe hyperplastic and hypertrophic growth of skeletal muscle. The results showed that skeletal muscle growth of mandarin fish included both increasing of fibre numbers (hyperplasia) and fibre area (hypertrophy) at the early development stage, the total fiber numbers in the right first dorsal myomere increased from 40 to 520, and the total fiber area increased from 805.30μm2 to 186422.77μm2. During the 1-9 days after hatching, the relative increased fiber numbers decreased and the relative increased fibre area rose slowly, the contribution rate of hyperplastic growth dropped dramatically from 60.53% to 8.8%, as opposite to hypertrophic growth. At the period of 9-15 days after hatching, the relative increased fiber numbers rose and relative increased area was on a steady phase, the contribution rate of hyperplastic growth increased from 8.8% to 20.26%, while hypertrophic growth contribution ratio decreased slightly. At the 15-41 days after hatching, both the relative increased fiber numbers and area were on the rise, the contribution rate of hyperplastic growth decreased to a steady phase and hypertrophic growth (from 79.76% to 87.41%) gradually became the dominant contributor of skeletal muscle growth.