Figure 1.

ATR disrupted the difference of axial muscle and the arrangement of muscle fiber of larvae treated at early embryonic stages. After hatching, the development of juveniles' sarcomere was observed in polarizing microscope photographs. At 2 dpf (a–e), the density of muscle fibers of all the groups including the control (a, DMSO) was low. Except for the group exposed to 0.001 mg ATR/L (b), there was no obvious differentiation of the fast and slow twitch. At 4 dpf (f–j), in the control group, the sarcomere developed normally, and the density of muscle fibers increased, but the differentiation of the fast and slow twitch was not significant (f); with the increase of concentration of ATR, the boundaries of muscle tended to be blurred (g–j, gradient ATR). The shape of sarcomere appeared to emerge at 6 dpf (k–o). In control group, the length (between the two vertical lines) of single sarcomere increased; muscle fibers were arranged stably (k); the organization pattern of ventral muscle fibers changed with the concentration of ATR (l–o, gradient ATR). The diagram at left upper corner was for the structure of sarcomere of bony fish trunk (gray for slow twitch in shallow sarcomere and white for fast twitch in deep sarcomere); the red box was for the photo display. In all photos, the dorsal of juvenile was up; the mouth was on the right side. Scale: 40 μm. 5 larvae were used for each experiment group (2 dpf, 4 dpf, and 6 dpf), repeated 6 batches.