Determination of total protein in hemolymph of the western rock lobster (Panulirus cygnus george) by refractometry

Abstract

Research on western rock lobsters (Panulirus cygnus) has shown that refractometry is a simple non-destructive field technique for assessing the hemolymph protein concentration and hence the tissue mass or "condition" of rock lobsters. However, a conversion from refractive index (RI) to protein concentration has not been published for this species. Hemolymph samples were obtained from the pericardial sinus of lobsters via the arthrodial membrane between the posterior margin of the carapace and the abdomen using disposable hypodermic syringes. In order to convert RI values to protein concentrations, the refractive index of a number of hemolymph samples were measured at ambient temperature using a Shibuya S-1 salinometer calibrated at ambient temperature with distilled water. Total protein concentrations were determined colourimetrically by the biuret method. Comparing the data gave the following regression equation: Total protein (mg/mL) = (5402.398 x RI) - 7214.877, r super(2) = 0.947, n = 28 This analytical method represents a simple, and useful way to obtain important information about the condition of rock lobsters entering commercial handling and transport. The measurement involves a straightforward physical phenomenon and it is probably not surprising that the conversion equation obtained in this study is similar to that derived from a study of the American lobster. These conversions may be a satisfactory method of estimating blood protein concentration in other large marine crustaceans. If large numbers of measurements are to be made for other species using this method, it is relatively easy to establish a calibration to ensure the accuracy of the technique.