The Phenotypic Plasticity Of Lateral And Cardiac Muscle Of Juvenile Southern Catfish Silurus Meridionalis With Different Nutritional Status

Three series of experiment were conducted in the warmwater, sit-and-wait foraging juvenile southern catfish (Silurus meridionalis Chen) at25±0.5℃using the technologies of histology, physiology and transmission electron microscope. In experiment one, the relative ventricular masses (RVM) of the juvenile southern catfish were examined under different starvation periods (0d,16d,32d,64d) and refeeding following these starvation periods. In experiment two, the effects of different starvation periods (0d,16d,32d,64d) on the structure of lateral muscle were examined. In experiment three, the effects of above four starvation treatments and refeeding on the key metabolic enzymes (e.g., Ca2+-ATPase, lactate dehydrogenase LDH, phosphokinase PK, succinic dehydrogenase SDH) of cardiac muscle and lateral muscle in this species. The results of present study as follows:The RVM of the juvenile southern catfish was0.122±0.017%, which was smaller than in some fishs that were studied on the same index. As to the control group, the RVM increased firstly and then decreased with postprandial time increased. During postprandial times of the S16group and S32group, the RVM had changed significantly. As to the S64group, the RVM of the southern catfish had showed no significant change during the postprandial period.Starvation has induced the great decrease of some key metabolic enzymes activity in cardiac muscle in the southern catfish. Only the Ca2+-ATPase activity of the S16group has up-regulated to the control level after refed. The LDH activity in the cardiac muscle decreased significantly after starvation. As the starvational time increased, LDH activity in cardiac muscle recovered to the pre-starved level. Refeeding can make the LDH activity of the S16group recover to the pre-starvation level, while both the S32group and the S64group did not show this trait. Starvation showed a initial increase and then decrease of the PK and SDH activities in the cardiac muscle (P<0.05) as the starvation time increased. The S32group showed the highest PK and SDH activities during the starvation period, which was significantly higher than in the control group, and both the S16d group and S64d group showed no significant change with the control group. As for S32d group, both PK and SDH activities have recovered to the control level after refeeding. The other two goups have showed no significant change after refeeding. Red muscle, which have high SDH activiy and was main at lateral line of the body, was less and smaller than white muscle,which have high PK, LDH, Ca2+-ATPase activities, in juvenile southern catfish. The cross-sectional area of the red muscle fibers was among180-420μm2, while the cross-sectional area of the white muscle fibers was1200-4200μm2. Both red muscle and white muscle fibers were in tight arrangement, and contained many myofibril, mitochondria, glycogen, sarcoplasmic reticulum. Myofibriis of both red and white muscle fibre have an outer layer of ribbon-like myofibrils,while the more centrally located myofibriis are small and polygonal. The tirads were located beside Z-line. The fibres of both red and white muscle showed the mosaic appearance in the transverse sections. During starvation, the cross-sectional area of the white muscle fibers decreased significantly, and the areas of white muscle fibers between each two starvational groups were significantly different (P<0.05). The cross-sectional area of the red muscle fibers decreased also profoundly during starvation. The cross-sectional area of the red muscle fibers of both S32group and S64group were much smaller when compared to the control group. Starvation was also associated with a degradation of the internal cristae structure of mitochondria, pycnosis and despearation of nucleolus, glycogen decreased and subsarcolemmal space swelled and substantial atrophy of both red and white muscle fiber.Starvation only resulted in the significant decrease of the Ca2+-ATPase activity in red muscle of the S64group. No significant changes in the LDH and PK activities were found during the starvation. Whereas the SDH activity has significantly decreased. All metabolic enzymes of S64d group in red muscle in present study did not recover to the control level after refed.The Ca2+-ATPase activity in white muscle of each starvational group was significantly lower than in the control group. Both LDH and Ca2+-ATPase activities decreased greatly after starvation. S16group had the lowest LDH activity and S64group had the lowest PK activity. No significant change in the SDH activity of the white muscle was test in S16d group, but decreased significantly in S32d group and S64d group (P<0.05). All metabolic enzymes of S64d group in white muscle in present study did not recover to the control level after refed.The main conclusions as follows:Juvenile southern catfish have a good tolerance to starvation, and the cardia can regulate fastly performance associate with starvation and refed. The physiological function of the cardia had no significantly change under the experiment condition in present research.The histructure, ultrastructure of the lateral muscle of juvenile southern catfish were simillar with the other fishes. The fibers of lateral muscle in juvenile southern catfish possessed the mosaic appearance in the transverse sections, which indicated the stage of fast growth and development of this fish. The developing fibers showed the mosaic appearance in the transverse sections. The distribution characteristics of myofibrils and metabolic traits of red and white muscle in the lateral muscle of juvenile southern catfish showed all adaptations to their life-style. After starvation, the instructure of the lateral muscle and the metabolic enzymes,which fromed the metabolic traits of red and white muscle showed significantly change. Such as LDH activity inwhite muscle and SDH activity in red muscle. Refed following long time of starvation(S64d) can not restore the metabolic enzymes. The metabolic enzymes responded to starvation with different changes traits that varied with starvational treatment and body physiologic adaptation. The muscle atrophy associtated with starvation might have a effect on the flesh quality and physiologic function of lateral muscle in juvenile southern catfish. The timely feeding needs to payed attention in the farming of juvenile southern catfish.