Alex Mustard / Yellowtail tang (Zebrasoma xanthurum) male and female turn belly to belly during spawning to ensure fertilization. Temple, Ras Umm Sid, Sharm El Sheikh, Sinai, Egypt. Red Sea. This action is very fast...

Gary Bell/ Oceanwide / Yellow-banded Snapper (Lutjanus adetii) school, Heron Island, Great Barrier Reef, Queensland, Australia

Gary Bell/ Oceanwide / Scarlet Cleaner Shrimp (Lysmata amboinensis) cleaning Yellow-edged Moray (Gymnothorax flavimarginatus), Tulamben, Bali, Indonesia

Alex Mustard / Two female Common seahorses (Hippocampus kuda) fighting over territory on the seabed. The brief fight was preceeded by a ritualised, synchronised parade. Bitung, North Sulawesi, Indonesia. Lembeh Stra...

Alex Mustard / Common seahorse (Hippocampus kuda) female wrapping her prehensile tail around piece of wood on the seabed. Bitung, North Sulawesi, Indonesia. Lembeh Strait, Molucca Sea.

Alex Mustard / Portrait of a male short snouted seahorse (Hippocampus hippocampus) in sea oak seaweed (Halidrys siliquosa). Devon, England, United Kingdom. British Isles. English Channel. North East Atlantic Ocean.

Nick Upton / European eel (Anguilla anguilla) elver migrating upstream, using an eel pass on the side of a weir, Somerset Levels, England, UK, July.

David Fleetham / Bargibant's pygmy seahorse (Hippocampus bargibanti) wrapped around Eye fan coral (Cnidaria sp). Philippines.

Dave Bevan / Male Blackbird (Turdus merula) catching European eel (Anguilla anguilla) elvers as they migrate up a waterfall, Ceredigion, Wales, UK, July.

Dave Bevan / Male Blackbird (Turdus merula) catching European eel (Anguilla anguilla) elvers as they migrate up a waterfall, Ceredigion, Wales, UK, July.

Dave Bevan / European eel (Anguilla anguilla) elvers migrating up a wet rock next to a waterfall, Ceredigion, Wales, UK, July.

Alex Mustard / Yellowtail tang (Zebrasoma xanthurum) male courting a female prior to spawning at dusk on a coral reef. Temple, Ras Umm Sid, Sharm El Sheikh, Sinai, Egypt. Red Sea.

David Fleetham / Cleaner wrasse (Labroides dimidiatus) swimming alongside Golden damsel (Amblyglyphidodon aureus) looking for parasites, Fiji, Pacific Ocean.

Alex Mustard / Ribbon sweetlips (Plectorhinchus polytaenia) USAT Liberty Wreck, Tulamben, Bali, Indonesia. Java Sea

Alex Mustard / Spotlight goby (Gobiosoma louisae) looking out from inside a Yellow tube sponge (Aplysina fistularis), growing on a coral reef. Bloody Bay Wall, Little Cayman, Cayman Islands, British West Indies. Car...

Alex Mustard / Red Irish lord (Hemilepidotus hemilepidotus) resting on a yellow sponge, in front of red soft coral (Eunephthya rubiformis). Browning Pass, Port Hardy, Vancouver Island, British Columbia. Canada. Nor...

Pascal Kobeh / Long-snouted seahorse (Hippocampus guttulatus) with prehensile tail twined round seagrass, Etang de Thau Lagoons, Languedoc-Roussillon, France.

Georgette Douwma / Blue triggerfish (Pseudobalistes fuscus). Egypt, Red Sea. Indo-Pacific.

Nuno Sa / Long snouted seahorse (Hippocampus guttulatus) in captive breeding laboratory at University of Algarve, Portugal. June 2010. Overall winner of the Underwater Photographer of the Year competition 2015.

Alex Mustard / Portrait of a Severn's pygmy seahorse (Hippocampus severnsi) at Mioskon Island, Raja Ampat, West Papua, Indonesia. Dampier Strait. Tropical West Pacific Ocean.

Alex Mustard / Black hamlet (Hypoplectrus nigricans) and Yellowbelly hamlet (Hypoplectrus aberrans) spawning at dusk. As this genus is quite recently evolved hybridization is still possible. Hamlets are one of the...

Alex Mustard / Saddleback anemonefish (Amphiprion polymnus) in anemone home, Anilao, Batangas, Luzon, Philippines. Verde Island Passages, Tropical West Pacific Ocean.

Alex Mustard / Harlequin sweetlips (Plectorhinchus chaetodonoides) cleaned by a pair of bluestreak cleaner wrasse (Labroides dimidiatus). South Atoll, Tubbataha Atolls, Tubbataha Reefs Natural Park, Palawan, Philipp...

Juan Manuel Borrero / Pearl cichlid (Geophagus brasiliensis) captive, occurs in Brazil and Uruguay.

Jurgen Freund / Blue and yellow fusiliers (Caesio teres) shoal, Great Barrier Reef, Queensland, Australia.

Pete Oxford / Yellow-tailed Surgeonfish (Prionurus laticlavius) school and snorkeler, Galapagos Islands, Ecuador

Pete Oxford / Yellow-tailed Surgeonfish (Prionurus laticlavius) school and snorkelers, Galapagos Islands, Ecuador

Constantinos Petrinos / Yellow stripe clingfish (Diademichthys lineatus) living in association with the Fire Urchin (Astropyga radiata) Lembeh Strait, North Sulawesi, Indonesia.

Franco Banfi / Freshwater Dorado (Salminus brasiliensis) Recanto Ecologico, Rio da Prata, Bonito, Mato Grosso do Sul, Brazil

Georgette Douwma / Coral reef scenery with a pair of Red Sea raccoon butterflyfish (Chaetodon fasciatus), Pygmy sweepers (Parapriacanthus guentheri) and soft corals (Dendronephthya sp) Egypt, Red Sea.

Jeff Rotman / Pectoral fin of a Steepheaded parrotfish (Chlororus gibbus) in the Red Sea, Egypt.

Jeff Rotman / Orangespine unicornfish (Naso lituratus) profile portrait, Red Sea, Egypt.

Alex Mustard / Butterfish (Pholis gunnellus) portrait. Gardur, south west Iceland. North Atlantic Ocean.

Alex Mustard,Alex Mustard / Portrait of a Yellow moray eel (Gymnothorax prasinus) - endemic to SE Australia. Chowder Bay, Sydney Harbour, New South Wales, Australia.

Franco Banfi,Franco Banfi / Ornate ghostpipefish, (Solenostomus paradoxus) Raja Ampat, Irian Jaya, West Papua, Indonesia, Pacific Ocean

Willem Kolvoort / Tetra (Moenkhausia surinamensis) under Apinagia leaves. Awadan rapids, Gran Rio, Suriname, September.

Claudio Contreras,Claudio Contreras / Long-beaked Coralfish (Chelmon rostratus) eye, Inanuran Island, Danajon Bank, Central Visayas, Philippines, April

Michael Pitts / Bicolour parrotfish (Cetoscarus bicolor) sleeping at night, Red Sea.

Mark Bowler / Silver arowana (Osteoglossum bicirrhosum) Amazonian fish occuring in Varzea flooded forests of the amazonian rainforest. These babies with their yolk sacks have been collected for the ornamental fish...

Fred Bavendam / Golden Damselfish (Amblyglyphidodon aureus), Tonga

Fred Bavendam / Pygmy Sweeper (Parapriacanthus ransonneti) school, Komodo Island, Indonesia

Chris Newbert / Squarespot Anthias (Pseudanthias pleurotaenia) female 50 feet deep, Papua New Guinea

Flip Nicklin / Queen Triggerfish (Balistes vetula) portrait off of Manualita Island on the west side of Cocos Island, Costa Rica

Chris Newbert / Scarlet Cleaner Shrimp (Lysmata amboinensis) pair cleaning a Moray Eel (Gymnothorax ocellatus) 80 feet deep, Solomon Islands

Norbert Wu / Green Sea Turtle (Chelonia mydas) being cleaned by Yellow-eyed Surgeonfish (Ctenochaetus strigosus), Hawaii

Claus Meyer / Blacktail Piranha (Pygocentrus piraya) underwater portrait, Amazon, Brazil

Chris Newbert / Yellow-striped Cardinalfish (Apogon cyanosoma) male with eggs in mouth, 40 feet deep, Solomon Islands

Chris Newbert / Soft Coral (Dendronephthya sp) schooling Pygmy Sweeper (Parapriacanthus ransonneti) and Lionfish (Pterois volitans)

Chris Newbert / Pygmy Sweeper (Parapriacanthus ransonneti) in cave

Chris Newbert / Pygmy Sweeper (Parapriacanthus ransonneti) school in cave, Red Sea, Egypt

Chris Newbert / Soft Coral (Dendronephthya sp) outcroppings, Sea Fan (Subergorgia sp) and Glassfish (Parapriacanthus ransonneti)

Fred Bavendam / Diagonal-banded Sweetlips (Plectorhinchus lineatus) school underwater, Great Barrier Reef, Queensland, Australia

Fred Bavendam / Diagonal-banded Sweetlips (Plectorhinchus lineatus) school, Great Barrier Reef, Queensland, Australia

Fred Bavendam / Yellowfin Goatfish (Mulloides vanicolensis) often gather in large schools during the day and disperse at night to feed, Great Barrier Reef, Queensland, Australia

Fred Bavendam / Long-snouted Seahorse (Hippocampus reidi) portrait, Bonaire, Netherland Antilles

Fred Bavendam / Yellowfin Goatfish (Mulloides vanicolensis) often gather in large schools during the day but disperse at night to feed, Great Barrier Reef, Queensland, Australia

Flip Nicklin / Queen Angelfish (Holacanthus ciliaris) juvenile, Cocos Island, Costa Rica

Fred Bavendam / Diagonal-banded Sweetlips (Plectorhinchus lineatus) school, Loloata Resort, Papua New Guinea

Fred Bavendam / Diagonal-banded Sweetlips (Plectorhinchus lineatus) school, Loloata Resort, Papua New Guinea

Fred Bavendam / Guineafowl Pufferfish (Arothron meleagris) in its golden color phase puffed up off of Tower Island, Galapagos Islands, Ecuador

Alex Mustard / Yellow longsnout seahorse (Hippocampus reidi) female holds onto a sea rod with its prehensile tail, on a coral reef. West Bay, Grand Cayman, Cayman Islands, British West Indies. Caribbean Sea.

Alex Mustard / Eye of a Masked butterflyfish (Chaetodon semilarvatus). This species is endemic to the Red Sea. Ras Mohammed National Park, Sinai, Egypt. Red Sea

Alex Mustard / Lemon coral goby (Gobiodon citrinus) shelters in the branches of a coral (Acropora sp.). Gubal Island, Egypt. Strait Of Gubal, Red Sea.

Alex Mustard / Pygmy lemon gobies ( Lubricogobius exiguus) guarding their home in a glass bottle (backlit with a torch). Anilao, Batangas marine protected area, Luzon, Philippines. Verde Island Passages, Tropical We...

Alex Mustard / Common seahorse (Hippocampus kuda) female gripping onto a piece of waterlogged wood with her prehensile tail. Bitung, North Sulawesi, Indonesia. Lembeh Strait, Molucca Sea.

Georgette Douwma / Kaleidoscopic image of Pygmy sweepers (Parapriacanthus guentheri) and soft corals (Dendronephthia sp.), Egypt, Red Sea.

Georgette Douwma / Kaleidoscopic image of Bigeye snappers (Lutjanus lutjanus) with soft corals. West Papua, Indonesia.

Georgette Douwma / Kaleidoscopic image of Pygmy sweepers (Parapriacanthus guentheri) with soft corals (Dendronephthia sp.), Egypt, Red sea.

Sergio Hanquet / Short-snouted seahorse (Hippocampus hippocampus). Tenerife, Canary Islands.

David Hall / Yellow prawn-goby (Cryptocentrus cinctus) and Snapping shrimp (Alpheus sp). Mutualistic symbiosis with goby as watchdog and shrimp maintaining burrow. Komodo, Indonesia.

David Hall / Many-eyed snake eel (Ophichthus polyophthalmus), head peering out of burrow. Pantar, Alor Archipelago, Indonesia; November, 2006.

Tony Wu / Korean sandlance (Hypoptychus dybowskii) egg clusters on Sargassum (Sargassum horneri). Fish produce sticky secretion in kidneys that adheres eggs to Sargassum. Hokkaido, Japan. May.

Gary Bell/ Oceanwide / Scarlet Cleaner Shrimp (Lysmata amboinensis) cleaning Yellow-edged Moray (Gymnothorax flavimarginatus), Tulamben, Bali, Indonesia

Shane Gross / Yellow clownfish (Amphiprion sandaracinos) in sea anemone, Indonesia.

Pascal Kobeh / Long-snouted seahorse (Hippocampus guttulatus), Canary Islands

Heather Angel / Bubble eye goldfish (Carassius auratus) with upward pointing eyes and two large fluid-filled sacs.. In captivity, Shanghai Zoo, Shanghai, China.

SCOTLAND: The Big Picture / European eel (Anguilla anguilla) migrating upstream bypassing a waterfall by leaving the water completely. Cairngorms National Park, Scotland, UK, July.

Franco Banfi / Shoal of colorful yellow fish Panamic porkfish (Anisotremus taeniatus), Cabo Pulmo Marine National Park, Baja California Sur, Mexico

Franco Banfi / Golden grouper (Mycteroperca rosacea), yellow color-variation of the most common leopard grouper species, Cabo Pulmo Marine National Park, Baja California Sur, Mexico

Franco Banfi / Golden grouper (Mycteroperca rosacea), yellow color-variation of the most common leopard grouper species, Cabo Pulmo Marine National Park, Baja California Sur, Mexico

Alex Mustard / Coral grouper (Cephalopholis miniata) waits in ambush, hiding against a seafan (Annella sp.) hunting silversides (Atherinidae), with schooling bigeye snapper (Lutjanus lutjanus) behind. Misool, Raja A...

Alex Mustard / Three moray eels, a Honeycomb moray: (Gymnothorax favagineus), Yellowmargin moray: (Gymnothorax flavimarginatus) and White-eyed moray (Gymnothorax thrysoideus) emerge from a single hole in a coral ree...

Alex Mustard / Common seahorse (Hippocampus kuda). The dark patch beneath his snout is his brood pouch. Bitung, North Sulawesi, Indonesia. Lembeh Strait, Molucca Sea.

Franco Banfi / Shoal of Bigscale soldierfish (Myripristis berndti), Dominica, Caribbean Sea, Atlantic Ocean

John Shaw / Yellow-billed cardinal (Paroaria capitata). Pantanal, Brazil, September.

Juergen Freund / Shortfin Lionfish (Dendrochirus brachypterus) and two Golden coral goby (Paragobiodon xanthosoma) using rubbish as their home, Sulawesi, Indonesia. November.

Juergen Freund / Black banded damselfish (Amblypomacentrus breviceps) and Yellow clown goby (Gobiodon okinawae) hiding in a discarded bottle, Sulawesi, Indonesia. November.

Juergen Freund / Saddleback clownfish (Amphiprion polymnus) surrounded by marine trash around its anemone home, Sulawesi, Indonesia. November.

Georgette Douwma / Blue or Rippled triggerfish (Pseudobalistes fuscus). West Papua, Indonesia. Indo-West Pacific.

Georgette Douwma / Pygmy sweepers (Parapriacanthus ransonetti). West Papua, Indonesia. Indo-West Pacific.

Gary Bell/ Oceanwide / Golden Damselfish (Amblyglyphidodon aureus), Great Barrier Reef, Australia

Gary Bell/ Oceanwide / Golden Anemonefish (Amphiprion sandaracinos) in sea anemone, Milne Bay, Papua New Guinea

Gary Bell/ Oceanwide / Latticed Butterflyfish (Chaetodon rafflesi), Anilao, Philippines

Gary Bell/ Oceanwide / Yellow-striped Cardinalfish (Apogon cyanosoma) sheltering in featherstar, Great Barrier Reef, Australia