Can fish "hold their breath"?

You'd think they wouldn't need to, but it turns out hammerhead sharks are weird in another way than their heads.

We're specifically talking about Sphyrna lewini, the scalloped hammerhead sharks. When diving, they close their gills. Why? To keep themselves warm...they're a warm water fish and the deep water is cold. And they can hold their breath for 17 minutes.

Do they have a "dive reflex" like mammals?

Is the dive reflex that old?