Ecological relevance of hemolymph total protein concentration in seven unrelated crustacean species from different habitats measured predictively by a density-salinity refractometer

In recent years, blood metabolites have been investigated as a tool for monitoring physiological condition in wild or culturedcrustaceans exposed to different environmental conditions. Blood protein levels fluctuate with changes in environmental andphysiological conditions and play fundamental roles in the physiology of crustaceans from O2 transport to reproduction upto stress responses. Proteins are major contributors to hemolymph density, and the present study correlates the easy and lowcost measure of hemolymph density by a density-salinity refractometer with the total protein concentration, measured witha colorimetric method. Moreover, the study evaluates the accuracy of the relationship and provides a conversion factor fromhemolymph density to protein in seven species of crustaceans, representative of taxa far apart in the phylogenetic tree andcharacterized by different life habits. Measuring serum-protein concentration by using a refractometer can provide a nondestructivefieldmethod to assess crustacean populations/species protein-relatedmodifications of physiological state without need of costly laboratory facilities and procedures.