Alex Mustard / Midnight snapper (Macolor macularis) shelters in a cavern on a coral reef with white soft corals (Scleronephthya sp.) and solderfish. Vavuu Atoll, Maldives. Indian Ocean

Alex Mustard / School of White collar butterflyfish (Chaetodon collare) pack together above a coral reef. North Male Atoll, Maldives. Indian Ocean

Alex Mustard / Pair of Western clown anemonefish (Amphiprion ocellaris) spawning orange eggs on the rock beneath their Magnificent sea anemone (Heteractis magnifica) home on a coral reef. This photo shows the larger...

Alex Mustard / Whitemargin stargazer (Uranoscopus sulphureus) sets an ambush in the sand at night. Bitung, North Sulawesi, Indonesia. Lembeh Strait, Molucca Sea.

Tony Wu / Fringed blenny (Chirolophis japonicus) guarding its eggs. Miyagi Prefecture, Japan.

Tony Wu / View down the throat of a male Zoarchias major eelpout (Zoarchias major) that has opened its mouth during a confrontation with another male. Yamaguchi Prefecture, Japan. Pacific Ocean.

Tony Wu / Two male Zoarchias major eelpouts (Zoarchias major) engaged in a mouth-to-mouth confrontation. Yamaguchi Prefecture, Japan, Pacific Ocean.

Tony Wu / Zoarchias major eelpouts. (Zoarchias major) The orange individual is female, the one in the hole is male. The female has approached the male, curled around him, attempting to dislodge the male from th...

Tony Wu / Zoarchias major eelpout (Zoarchias major) with her mouth wide open. Yamaguchi Prefecture, Japan, Pacific Ocean.

Alex Mustard / Forster's hawkfish (Paracirrhites forsteri) on a coral reef. Jackson Reef, Tiran, Sinai, Egypt. Strait of Tiran, Gulf of Aqaba, Egypt.

Shane Gross / Pelagic thresher shark (Alopias pelagicus) cleaned by a Bluestreak cleaner wrasse (Labroides dimidiatus) at Monad Shoal off Malapascua Island, Philippines.

Shane Gross / Pelagic thresher shark (Alopias pelagicus) being cleaned by a bluestreak cleaner wrasse (Labroides dimidiatus) at Monad Shoal off Malapascua Island, Philippines.