Alex Mustard / Portrait of Blacktip grouper (Epinephelus fasciatus) resting in Barrel sponge (Xestospongia testudinaria) Mabul Island, Sabah, Borneo, Malaysia. Sulawesi Sea.

David Fleetham / Tiger rockfish (Sebastes nigrocinctus). British Columbia, Canada.

Alex Mustard / Sixbar grouper (Cephalopholis sexmaculata) in overhang on a coral reef. South Ari Atoll, Maldives. Indian Ocean.

Alex Mustard / Shoal of a Red Sea soldierfish (Myripristis murdjan) and Sixbar grouper (Cephalopholis sexmaculata) shelter in a coral filled cave. Ras Mohammed National Park, Sinai, Egypt. Red Sea.

Pascal Kobeh / Saddle grouper / Sixspot rockcod (Cephalopholis sexmaculata) with White-edged soldierfish (Myripristis murdjan) in a cave, Maldives. Indian Ocean.

Michael Pitts / Orange-striped triggerfish (Balistapus undulatus) and Sixspot groupers (Cephalopholis sexmaculata) on a sunken shipwreck, Maldives, Indian Ocean.

Alex Mustard / Portrait of cave dwelling Saddled grouper (Cephalopholis sexmaculata) in Ras Mohammed Marine Park. Sinai, Egypt. Red Sea.

Georgette Douwma / Blacktip grouper (Epinephelus fasciatus) Egypt, Red Sea.

Shane Gross / Researcher Hailey Davies uses Downrigger and action camera to monitor the lowering of a tiger rockfish (Sebastes nigrocinctus) for a study on fish barotrauma, whereby the gases in a fish expand as it...

Shane Gross / Researcher Hailey Davies uses Downrigger and action camera to monitor the lowering of a tiger rockfish (Sebastes nigrocinctus) for a study on fish barotrauma, whereby the gases in a fish expand as it...