水产养殖 矿物质营养.pptVIP

Calcium and Phosphorus Dietary calcium can be absorbed from the intestine by active transport (dependent on physiological requirements) Mineral absorption depends upon whether the mineral is soluble at the pH of the gut Minerals have a higher availability if water soluble Presence of acidic stomach increases availability calcium, for example, can be put in the diet as calcium lactate (58%), tribasic calcium phosphate (37%) or calcium carbonate (27% availability) Calcium and Phosphorus In vertebrates Blood levels of Ca and P are regulated by PTH(甲状旁腺激素) and cholecalciferol Low levels of Ca in blood trigger the release of PTH which facilitates the production of 1,25(OH)D3 Low levels of P stimulate the production of 1,25(OH)D3 Calcium binding protein (controls Ca and P absorption) in intestine Cellular functions that control deposition/mobilization from structural tissues and kidney re-absorption Function is similar in fish but the scales appear to have a higher exchange rate for Ca than bone. Availability of Ca and P Form in which it is included in the diet Solubility at luminal pH (acidic stomach) Level of lactose intake (lactose increases availability of Ca) Vitamin D Mineral interactions: iron, aluminum, manganese, potassium and magnesium Fat intake (Ca forms insoluble soaps) Nutrient status of the animal (compensatory response) Calcium and Phosphorus A dietary source of calcium is not required for fish or shrimp grown in water with suitable levels of calcium! Ca is absorbed from the water Phosphorus is generally low in most natural waters, there is a dietary requirement. It has also been shown that supplementation of high levels of calcium to the diet inhibits phosphorus availability thus, dietary ratios 2:1 Ca:P are recommended Phosphorus Constitutes the primary expense for mineral supplement Environmental pollutant that is regulated in many countries (over-supplementation and biological availability are critical issues) Dietary requirement (available P/100g