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Declining wild sturgeon populations around the world have led to a significant increase in the production of farm-raised caviar, but sturgeon farmers face difficult challenges to produce eggs of sufficient size and firmness to yield high-quality caviar. Females reach sexual maturity at about seven years and the eggs are examined by biopsy in late autumn for color and size. The exact time of harvest to produce optimum quantity and quality of caviar cannot be predicted based on egg size or color at the time of biopsy because of individual variation in the rate of egg growth and development. The overall goal of this research is to conduct the preliminary work on sensor development and maturity prediction to give sturgeon farmers better methods to optimize the quantity and quality of harvested caviar. During the ovarian cycle, eggs sequester the yolk precursor vitellogenin, a glycolipophosphoprotein secreted into the bloodstream by the liver. Changes in the concentration of circulating vitellogenin reflect development and growth of the eggs. The total calcium concentration in the plasma of sturgeon is highly correlated with vitellogenin concentration. Total calcium can be measured directly in the laboratory by atomic absorption spectrophotometry or by inductively coupled plasma mass spectrometry. For our research we chose a simple diagnostic assay commercially available for measurement of free calcium and most bound calcium in fluid samples. A miniature sensor platform using micro-pumps and micro-valves was designed to run the assay, with a complete testing cycle of less than 3 minutes. Calibration was done using standards made with calcium chloride in distilled water over the approximate range of physiological concentrations of total calcium in blood plasma. Preliminary tests were conducted on calcium chloride standards and on plasma from an immature female white sturgeon and a vitellogenic female green sturgeon. The sensor estimates differed somewhat from the known concentrations for the calcium standards, but were generally consistent with our expectations for blood plasma. The sensor was able to measure most of the total calcium in plasma and, thus, distinguish vitellogenic fish. Additional tests will be conducted with white sturgeon to determine the relationships between plasma calcium and egg development.