Sustainable Marine Aquaculture

EVALUATION OF REFRACTOMETRY AS A TOOL FOR MEASURING CHANGES IN BLOOD CHEMISTRY OF FISH REARED AT DIFFERENT SALINITIES

Research Team:
Marty Riche (USDA) - Principle Investigator
Chuck Weirich (USDA)
Dave Haley

As part of our study of the salinity tolerance of euryhaline fish species such as pompano, and flounder, we are working to develop reliable analytical tools that will help us to measure the effects of variations in environmental salinity on blood chemistry. One of the most important effects of changes in environmental salinity on blood chemistry is on blood serum protein levels. Colorimetric procedures for the determination of total serum protein are relatively expensive and lead to disposal problems of hazardous chemicals. Refractometry offers a low-cost, environmentally friendly alternative method for determining total serum protein. Refractometry measures totals solids in plasma or serum, therefore results will be influenced by differences or fluctuations in environmental salinity. However, current refractometry uses conversion tables designed for human and mammalian blood. The purpose of this study is to correlate of blood solute levels of fish reared over wide range of salinities with the refractive index of serum protein. The development of predictive equations allowing use of refractometry for determining serum protein in euryhaline species will make refractometry a useful tool for determining total serum protein levels in pompano.

Four groups of pompano (30 - 35 fish) will be acclimated to either 3, 11, 19, or 27 g/L salinity and stocked into 1000-L tanks operating as recirculating systems at the assigned salinity and maintained at 28 C. Fish will be fed twice a day to apparent satiation. Following 21 days in their assigned experimental conditions, fish will be anesthetized in 50 ppm MS-222 and sampled. Whole blood samples will be analyzed with an I-Stat portable clinical analyzer to obtain Na+, K+, Cl-, urea-N, glucose, pH, PCO2, hematocrit, HCO3, and total CO2. Plasma will be evaluated for osmolality. Plasma and serum will be analyzed for total protein using a temperature compensated refractometer, and reassessed with a colorimetric assay for total serum protein. Stepwise multiple regression analysis will be performed on selected parameters for the development of predictive equations and appropriate correction factors.