Every single one. Note the pruning cuts to separate the fruits from sharp angles, where they will be trapped and rot, and the edges of the twigs tipped to help the tree lay down next year’s twig in a place to renew this one.
Poor Man’s Bonsai!
Thinning will follow in June, to complete the selection, removing scarred fruits first, spacing the rest, and removing any remaining trapped fruits. There are millions of nectarine trees, each with hundreds of fruits, and each one is chosen by hand and eye, every single one.