Study On Selenium Deficiency Symptom And Mechanism And Requirement In Juvenile Common Carps

Four experiments were conducted to study Se requirement and deficiency symptom and molecular mechanism in juvenile carps with purified diets.Experiment 1: 360 juvenile common carps(Cyprinus carpio) with initial body weight 12.6±0.8g were randomly divided into 4 groups with triplicate and 30 carps per replicate, and were fed purified diets supplemented with selenium(Se, NaSeO₃, AR) 0, 0.15, 0.30, 0.45 mg/kg respectively for 30 weeks. By establishing experimental model of carps with selenium deficiency, the pathology and hematology were studied. The results indicated that the morbidity and mortality were 46.7%, 33.3%, 13.3%, 0 and 26.7%, 16.7%, 6.7%, 0 respectively.The carps fed Se deficient diet showed thin back disease and lordosis. Anatomical pathology showed that the muscle at the both side of the carps back became thin and looked like knife blade, muscular dystrophy and white muscle. The liver and spleen were swollen with hyperemia and hemorrhage. The examination of histopathology showed nutritional muscular dystrophy, hepatosis, degeneration and necrosis of pancreas. The skeletal muscles showed degeneration, necrosis and muscular atrophy. The cardiac muscle fibers showed swelling and necrosis. The cardiac muscles showed cellular swelling and degeneration. The hepatocyte showed degeneration and necrosis, even disappeared. The pancreas follicle showed degeneration and necrosis. The spleen showed haemorrhage, lymph cells were reduced, phagocyte increased and formed black phagocyte centre. The renal tubular epithelial cells showed swollen and deteriorative. The neuron cells showed swollen and deteriorative nerve was observed occasionally. In ultra-structure, the mitochondria of the skeletal muscle fibers, liver cells and renal tubular epithelial cells showed swelling, broken back, even disappeared, shaped follicles. The spleen cells showed hemorrhage and dropsy, lymph cells were necrosis. In hematology, erythrocyte haemoglobin amount and IgM were reduced, leukocyte amount and erythrocyte fragility increased, MDA, AST, ALT and LDH in serum increased, but the activities of GPx, SOD and CAT were reduced.Experiment 2: 270 juvenile common carps(Cyprinus carpio) with initial body weight 15.5±0.7g were randomly divided into 3 groups with triplicate and 30 carps per replicate, and were fed purified diets supplemented with selenium(Se,NaSeO₃, AR) 0, 0.25, 0.50 mg/kg respectively for 16 weeks. NO content, NOS activities in serum and liver and hepatocyte apoptosis were studied at 4th, 8th, 16th week respectively. The results showed that Se deficiency increased NOS activity and NO content in serum and liver(P<0.05). Se deficiency induced hepatocyte apoptosis. The characteristics of apoptotic hepatocyte showed that the chromatin of hepatocyte concentrated and moved to one side, and looked like half-moon shape and then cracked, the characteristic apoptosis bodies with the complete cytoplasm membrane were seen. The hepatocyte apoptosis percentage increased with the test time. The hepatocyte apoptosis induced by Se deficiency was mediated by NO free radicle in juvenile carps.Experiment 3: 1200 juvenile common carps(Cyprinus carpio) with initial body weight 10.4±0.4g were randomly divided into 10 groups with triplicate and 40 carps per replicate, and were fed diets supplemented with selenium(Se,NaSeO₃, AR) 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 mg/kg respectively for 90 days.The results showed that as Se supplemented was raised,the weight gain and survival rate of carps increased, feed conversion efficiency were reduced, and the performance was best in the group with 0.4 mg/kg Se(P<0.05). When the diets were supplemented with 0.3～0.5 mg/kg Se, head kidney weight: body weight and spleen weight: body weight of carps were higher(P<0.05), blood red cell amount increased and leukocyte amount decreased, survival rate and serum lysozyme activity 15d after vaccination against Aeromonas hydrophila increased significantly(P<0.05), valence of agglutinating antibody 17d after vaccination against Aeromonas hydrophila increased.Thus the immune function and resistance to disease of juvenile carps were improved. GPx activities in serum and liver increased significately(P<0.05). Se contents in blood and tissue were also raised significately(P<0.05). The relationship between Se and the weight gain, feed conversion efficiency, head kidney weight, spleen weight, serum lysozyme activity, IgM showed the remarkable quadratic curve relation. The most suitable Se requirement was 0.517, 0.499, 0.434, 0.447, 0.480, 0.464 mg/kg respectively according to the upper indices.Experiment 4: 160 juvenile common carps(Cyprinus carpio) with initial body weight 15.3±0.8g were randomly divided into 4 groups with 2 replicates and 20 carps per replicate, and were fed purified diets supplemented with selenium(Se,NaSeO₃, AR) 0,0.15, 0.3 and 0.45 mg/kg respectively for 8 weeks. The IGF-â… mRNA and GPx mRNA in the liver of carps were determined with RT-PCR. The results showed that the dietary Se increased IGF-â… mRNA and GPx mRNA expression significantly(P<0.05), as Se supplemented was raised, IGF-â… mRNA and GPx mRNA expression increased also.