Effects Of Dietary Magnesium Sulfate And Magnesium Glycinateinhibitory On The Growth And Physiology Of Japanese Seabass(Lateolabrax Japonicus)

The effects of magnesium (Magnesium sulfate or Magnesium glycine) at different levels indiet on the growth performance, lipid metabolism, muscle quality, antioxidant capacity and ionmetabolism of Japanese seabass (Lateolabrax japonicus), were investigated to explore themagnesium requirements of Japanese seabass, and the effects of Magnesium sulfate (inorganicmagnesium, IM) or magnesium glycine (organic magnesium, OM) on the growth and physiologyof Japanese seabass.1. Effects of different dietary magnesium levels on the growth performance and lipid metabolismof Japanese seabassMagnesium sulfate (inorganic magnesium, IM) or magnesium glycine (organic magnesium,OM) was supplemented to basic diet, respectively, to formulate7experimental diets with Mglevels (412(basic)、683(IM)、972(IM)、1893(IM)、702(OM)、1028(OM)、1935(OM)) mg/kgfor56d. Each diet was randomly assigned to three tanks; each tank was stocked with20Japanese seabass (initial body weight was23.2±0.2g). The results showed that: SGR and WGRof Japanese seabass increased with increasing dietary Mg level (P<0.05), and the peak value wasobserved in972mg/kg (IM) and1028mg/kg (OM) group. There were no effects of dietarymagnesium on the whole body content of Japanese seabass. With the increase of dietarymagnesium level, the contents of liver protein and liver lipid of Japanese seabass were increased.Serum TG increased significantly with increasing dietary Mg from400to1000mg/kg, and thendecreased significantly (P<0.05), and, which in IM groups were significantly lower than that inOM groups (P<0.05). There was similar variation of serum LDL-C and TG, however, LDL-C inIM groups were significantly higher than that in OM groups (P<0.05). Variation in serumHDL-C showed a reverse trend to that in LDL-C (P<0.05). Except for683mg/kg IM group,serum CHO in fish fed diets supplemented with Mg were significantly higher than that fed basicdiet (P<0.05), and there were no significant differences among all treatments supplemented withMg. Serum Lipoprotein lipase activity decreased significantly with increasing dietary Mg level(P<0.05), and the lowest value was observed in972mg/kg (IM) and1028mg/kg (OM) group.The results indicated that about1000mg/kg dietary Mg can improve growth and promote lipid anabolism of Japanese seabass in freshwater.Liver carnitine acyltransferase and acyl CoA synthetase activities significantly withincreasing dietary Mg from400to1000mg/kg, and then decreased significantly (P<0.05). In IMgroups, liver fatty acid synthetase activity decreased with increasing Mg level, and the lowestvalue was observed in1893mg/kg Mg group, in OM groups, Except for1028mg/kg, liver fattyacid synthetase activity in fish fed diets supplemented with Mg were significantly higher thanthat fed basic diet (P<0.05). With the increase of dietary magnesium level, serum insulinincreased in IM groups, and the peak value was observed in1893mg/kg Mg group, while in OMgroups, serum insulin increased slowly and then decreased, and the largest value was observed in1028mg/kg Mg group. Serum epinephrine significantly decreased and the increased with theincrease of dietary magnesium level in IM groups, there was similar variation of Serumepinephrine in OM groups, but the change was not significant.2. Effects of different dietary magnesium levels on the muscle quality and antioxidant capacity ofJapanese seabassWith the increase of dietary magnesium level, drip loss significantly decreased in OMgroups and slightly decreased in IM groups. The content of MDA in muscle decreased and thenincreased with the increase of dietary magnesium level in IM and OM groups, the lowest valuewere observed in972mg/kg (IM) group and1028mg/kg (OM) group. With the increase ofdietary magnesium level, total superoxide dismutase content of liver increased and thendecreased, the peak value were observed in972mg/kg (IM) group and1028mg/kg (OM) group,total antioxidant capacity and Glutathione peroxidase of liver had the similar trend with SOD,and the content of SOD, T-AOC and GSH-PX in OM groups were more than the correspondingIM groups. The content of MDA in liver showed a reverse trend to SOD, the lowest value wereobserved in972mg/kg(IM) group and1028mg/kg(OM)group, there is no difference in IMgroup with corresponding OM group. Liver Catalase in fish fed diets supplemented with Mg(OM groups) were significantly higher than that fed basic diet, but slightly increased in IMgroups.3. Effects of different dietary magnesium levels on the Ion metabolism of Japanese seabassCompared with the basic group, the content of Na+in serum had little change in IM groups,while in OM groups, the content of Na+in serum decreased significantly (P<0.05). Withincreasing dietary magnesium level, in IM groups, the content of K+in fish increased and thendecreased (P>0.05), the most value was observed in972mg/kg group, and there was anincreasing trend in OM groups (P<0.05), the content of K+in OM groups were more than the corresponding IM groups(P<0.05). Compared with the basic group, In addition to the972IMgroup and1893OM group, the content of Mg2+in spine increased significantly other groups,Dietary magnesium levels had little effect on the content of Cu2+in liver.