(Edited 2021-02-04 to explain what obligate ram ventilators do.)

A- and I have been curious about which shark species are obligate ram ventilators and need to keep swimming with their mouths open in order to get oxygen from the water flowing through their gills. Here is an incomplete list. (Disclaimer: We're not marine biologists and have no idea what we're doing.)

20210128_121612 Obligate ram ventilators #nature #sketch.jpg

1. Great white shark (Carcharodon carcharias) Source
2. Bull shark (Carcharhinus leucas) Source
3. Sandbar shark (Carcharhinus plumbeus) Source
4. Porbeagle (Lamna nasus) Source
5. Salmon shark (Lamna ditropis) Source
6. Thresher shark (Alopiidae) Source
   • Pelagic thresher (Alopias pelagicus)
   • Bigeye thresher (Alopias superciliosus)
   • Alopias vulpinus
7. Mako shark (Isurus oxyrinchus, Isurus paucus) Source
8. Hammerhead (Sphyrnidae) Source
   • Winghead shark (Eusphyra blochii)
   • Scalloped bonnethead (Sphyrna corona)
   • Carolina hammerhead (Sphyrna gilberti)
   • Scalloped hammerhead (Sphyrna lewini)
   • Scoophead (Sphyrna media)
   • Great hammerhead (Sphyrna mokarran)
   • Bonnethead (Sphyrna tiburo)
   • Smalleye hammerhead (Sphyrna tudes)
   • Smooth hammerhead (Sphyrna zygaena)
9. Whale shark (Rhincodon typus) Source

Some fishes are also obligate ram ventilators. Here is an incomplete list:

• Tuna Source
• Billfish Source – Structural Adaptations for Ram Ventilation: Gill Fusions in Scombrids and Billfishes
• Paddlefish (Polyodon) Source
• Swordfish Source
• Bonito Source – Structural Adaptations for Ram Ventilation: Gill Fusions in Scombrids and Billfishes
• Bluefish Source

So… how do they keep swimming? What about sleep?

Apparently, part of their brain stays active and keeps them swimming. Also, sometimes they rest in currents with their mouth open. Source