The Apple Watch has already seized second place behind health tracker Fitbit in the fast-growing market of wearable devices, IDC research said.

The wrist gadget’s share of the category was nearly 20 percent after shipping 3.6 million units during the second quarter. Fitbit’s share, by comparison, was 24 percent after shipping 4.4 million units, IDC said.

“Fitbit only sells basic wearables — a category that is expected to lose share over the next few years, leaving Apple poised to become the next market leader for all wearables,” the report said.

Fitbit shares fell 8.9 percent, to $34.97. Apple shares rose 2.9 percent, to $112.92.