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 C0, reaching a maximum at stage D2. 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, Ca2+ hemolymph concentrations decreased significantly between stages A and C0, and then increased significantly by nearly 60% up until stage E. Total calcium levels in the hepatopancreas were highest at stage C0. 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 C0, the cuticle was highly calcified, and calcium occurred until a distance of 135 μm from the surface at stage C0. In addition, the cuticle consisted of the present layer and a newly-forming layer. Calcium content was lower at stage D2, but calcium still existed in the exocuticle. At stage E (discarded cuticle), the cuticle consisted of the exocuticle layer only.