In an aerator (10) for aquariums and ponds there is an impeller (60) operated by an electric motor (20) having a first entry (246, 347) for the intake of water, a second entry (44) for the intake of air and an exit (254) where the water and air flow comes out, the impeller (60), when it is operated, sucks water from said first entry (246, 347), creates a lower pressure which sucks air from said second entry (44) and mixes said sucked air with water generating a flow which comes out from the exit (254).