Changes in the levels, expression, and possible roles of serotonin and dopamine during embryonic development in the giant freshwater prawn, Macrobrachium rosenbergii

• 5-HT and DA showed the highest levels at late embryonic stages.
• 5-HT was first detected in the early embryonic stages, whereas DA developed later.
• 5-HT shortened embryonic period, while DA exhibited an opposite effect.
• 5-HT and DA may be involved in embryonic development of this crustacean species.

We investigated the changes in the levels of serotonin (5-HT) and dopamine (DA), and their possible roles during embryonic development of the freshwater prawn, Macrobrachium rosenbergii. The 5-HT and DA concentrations were quantified using high performance liquid chromatography with electrochemical detection (HPLC-ECD). The levels of 5-HT and DA gradually increased from early developing embryos to late developing embryos. The 5-HT concentrations gradually increased from the pale yellow egg to orange egg stages, and reaching a maximum at the black egg stage. DA concentrations were much lower in the early embryos than those of 5-HT (P < 0.05), and gradually increased to reach the highest level at the black egg stage. Immunohistochemically, 5-HT was firstly detected in the early embryonic stages, whereas DA developed later than 5-HT. Functionally, 5-HT-treated female prawns at doses of 2.5 × 10−5, 2.5 × 10−6 and 2.5 × 10−7 mol/prawn, produced embryos with significantly shortened lengths of early embryonic stages, whereas DA-treated prawns at all three doses, exerted its effects by significantly lengthening the period of mid-embryonic stage onwards. These results suggest significant involvement of 5-HT and DA in embryonic developmental processes of this species.