Effects Of Organic Chromium Supplementation On Growth Performance And Gene Expression Of Glucose Metabolism In Nile Tilapia (Oreochromis Niloticus)

Trivalent chromium (Cr³⁺) is an essential trace element for animals. As an activecomponent of the glucose tolerance factor （GTF）, Cr³⁺is thought to alleviate glucoseintolerance and improve the metabolism of carbohydrate by enhancing the action of insulin andplaying an important role in insulin signaling. Nile tilapia （Oreochromis niloticus） was selectedas a model species in the present research. This research is not only to investigate the effect ofdifferent forms and different supplemental levels of organic chromium on the growthperformance, blood biochemistry and body composition, but also to determine the influence oforganic chromium on gene expression of insulin receptor （IR） and glucose transporter （GLUT）relating to glucose metabolism from a molecular perspective. The aim is to discuss themolecular mechanism of the effect of organic chromium on glucose metabolism and to providethe theoretical basis and practical guidance of the supplementation of organic chromium on fishfeed.525fish （initial mean weight of15.8±0.02g） in health condition were randomly distributedin to7trail groups. Each trail group was randomly assigned in triplicate to groups of25fish.Chromium picolinate （Cr-P） and chromium yeast （Cr-Y） were used as dietary chromium forms.Trial groups were fed on the basal diets with0.2,0.4,0.8mg/kg chromium in form of Cr-P orCr-Y. The Control group was fed on basal diet with0mg/kg chromium. The feeding experimentlasted50days in automatic water-circulated systems. The results of this study are as follows:1. The result of the growth showed that the different levels of Cr-P and Cr-Ysupplementations did not significantly affect the survival, weight gain ratio （WGR）, specialgrowth ratio （SGR） or feed conversion ratio （FCR） of Nile tilapia （P＞0.05）. However, WGRand SGR showed an increasing tendency with dietary Cr-P levels. 2. The result of the blood biochemistry showed that Cr-P and Cr-Y did not significantlyimprove the total protein （TP）, total cholesterol （TC）, triglycerides （TG）, blood urea nitrogen（BUN）. However, the serum glucose decreased with increasing levels of Cr-P and Cr-Ysupplementation and the lowest value was observed in0.8mg/kg Cr-Y group.3. The results of the body composition showed that fish in the100mg/kg Cr-P group hadsignificantly lower crude lipid contents of the whole body than the fish in the control diet （P＜0.05）. Fish fed0.8mg/kg Cr-P diet had the lower crude lipid content in the dorsal muscle thanfish fed the control diet （P＜0.05）. Moreover, the crude lipid content in the whole body anddorsal muscle increased with the increasing levels of Cr-P and Cr-Y supplementation. However,neither Cr-P supplementation nor Cr-Y supplementation had apparent effects on the moistureand crude protein contents of the whole body and dorsal muscle （P＞0.05）.4. The gene expression results revealed that insulin receptor （IR） mRNA expression inliver and muscle was not affected by Cr-P supplementation or Cr-Y supplementation （P＞0.05）.Cr-Y did not exert any effect on GLUT4expression in muscle, either （P＞0.05）.The glucosetransporter2（GLUT2） mRNA expression level in liver was higher with the0.8mg/kg Cr-P dietand the0.8mg/kg Cr-P diet than with0.4mg/kg Cr-P diet and0.2mg/kg Cr-P diet （P＜0.05）.The glucose transporter4（GLUT4） expression level in the muscle was higher in the0.8mg/kgCr-P group than in the0.4mg/kg Cr-P group （P＜0.05）.In summary, the results of this study showed that dietary Cr-P and Cr-Y supplementationsimproved the body composition and GLUT expression of Nile tilapia although they did notsignificantly improve the growth or blood parameters, which suggested that organic chromiumsupplementation had a potential ability to improve the glucose utilization of fish.