Rapid progestin stimulation of sperm motility is a widely observed phenomenon in vertebrates, but the mechanisms governing these effects are still poorly understood, especially in teleosts, amphibians, and birds, which do not express CatSper. Here we show that progestin-stimulated sperm hypermotility in a teleost, Atlantic croaker (Micropogonias undulatus), is initiated though membrane progestin receptor-alpha (mPRalpha, also known as Paqr7b) and involves activation of the Pi3k/Akt pathway and increased phosphodiesterase (Pde) activity. The specific mPRalpha agonist 10-ethenyl-19-norprogesterone (Org OD 02-0) mimicked the stimulatory actions of the endogenous progestin in this species, 17, 20beta, 21-trihydroxy-4-pregnen-3-one (20beta-S), on sperm motility. Inhibition of Pi3k (1 nM Wortmannin; 25 μM LY294002) and Akt (25 μM ML-9) effectively abolished progestin-initiated sperm hypermotility. Surprisingly, treatment with the PDE inhibitors Cilostamide (100 nM) and Rolipram (1 μM) also blocked progestin stimulation of sperm motility. Whereas treatment with 20beta-S increased sperm Pde activity, pretreatment with Wortmannin eliminated this response to the progestin and also resulted in elevated cAMP levels, indicating that Pdes are at least partially under Pi3k/Akt control. The results suggest that mPRalpha-mediated progestin stimulation of sperm motility in croaker through Pi3k/Akt is dependent on maintenance of Pde activity and a reduction in internal cAMP concentrations. However, a previous study showed that progestin stimulation of sperm hypermotility in this species is also dependent on membrane adenylyl cyclase (Acy) activation and increased intrasperm cAMP concentrations. Collectively, these findings indicate that progestin-mediated hypermotility through mPRalpha in teleost sperm involves modulation of intracellular cAMP concentrations through multiple signaling pathways.