Hemolymph osmolality, ion concentrations and calcium in the structural organization of the cuticle of the giant freshwater prawn Macrobrachium rosenbergii: Changes with the molt cycle

In the giant freshwater prawn, Macrobrachium rosenbergii, hemolymph osmolality was low at post-molt stages A and B, and increased gradually until intermolt stage C 0, reaching a maximum at stage D 2. Levels were lowest at the ecdysis (E) stage. Na + and Cl - hemolymph concentrations showed a pattern similar to that of osmotic concentrations during the molt cycle. On the other hand, Ca 2+ hemolymph concentrations decreased significantly between stages A and C 0, and then increased significantly by nearly 60% up until stage E. Total calcium levels in the hepatopancreas were highest at stage C 0. In parallel with hemolymph ionic changes, the distribution of calcium in the cuticle was analyzed using scanning electron microscopy–electron dispersion spectrometry (SEM–EDS). At the post-molt stage, calcium content was low, and the cuticle consisted of one layer. At stage C 0, the cuticle was highly calcified, and calcium occurred until a distance of 135 μm from the surface at stage C 0. In addition, the cuticle consisted of the present layer and a newly-forming layer. Calcium content was lower at stage D 2, but calcium still existed in the exocuticle. At stage E (discarded cuticle), the cuticle consisted of the exocuticle layer only.