This is Ava. She is a My Magical Seahorse from Zuru - the makers of the ever-popular ROBOfish.
Lara and Holly are both absolutely fascinated with their robo seahorse; so much so that I'm thinking of buying it a tank all of its own! Then we may need to buy a whole family of My Magical Seahorses (Ava, Coral and Jewel) to go in it.
My Magical Seahorse is from ZURU and available from all good UK toys stockists (rrp: £9.99). You can find them in Argos, Amazon, Smyths Toys and Tesco, among other places.