Most raptors have three toes forward and one back. The osprey shares with owls a reversible outer toe, and uses it at the moment of capture, closing on the fish from four directions rather than three. The grip is completed by spicules, short spiny projections on the foot pads that bite into scales.
The rest of the anatomy follows the same specialisation. The nostrils can be closed against water on entry, the plumage is dense and oily, and the legs are long relative to the body. Ospreys carry prey head-forward, which is usually explained as reducing drag, though the bird also simply grips where the fish is easiest to hold.
Hunting success is often quoted at around one in four dives, but published rates range widely with water clarity, wind and fish species, from roughly a quarter to well over half. A single headline number for the species is not supportable.