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...

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...

Tony Wu / Humphead parrotfish (Bolbometopon muricatum) shoal spawning in early morning, part of mass aggregation of thousands of fish. Caroline Islands, Palau.

Nick Hawkins / Chum salmon (Oncorhynchus keta) migrate up a small river near Bella Bella, British Columbia, Canada. September

Shane Gross / Elkhorn corals (Acropora palmata) at night silhouetted by a scientist's light during the annual coral spawn. Abaco, Bahamas.

John Cancalosi / American toads (Anaxyrus americanus), several males competing to mate with female, Maryland, USA, April.

Kerstin Hinze / Male Common european toad (Bufo bufo) in amplexus with a dead fish, Lower Saxony, Germany, April.

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.

Remi Masson / Group of Barbels (Barbus barbus) spawning, River Rhone, Rhone-Alpes, France, April.

Nick Hawkins / Atlantic salmon (Salmo salar) migrating for spawning in river, Gaspe Peninsula, Quebec, Canada, October.

Remi Masson / Group of Nase (Chondrostoma nasus) and Barbels (Barbus barbus) spawning, River Rhone, Rhone-Alpes, France, April.

Remi Masson / Shoal of Nase (Chondrostoma nasus) spawning, River Ain, Rhone-Alpes, France, April.

Michel Roggo / Atlantic salmon (Salmo salar) migrating upstream to spawn, Quebec, Canada Photographed for the Freshwater Project.

John Waters / Pair of Brown trout (Salmo trutta) spawning, with others eating eggs, River Kennet, Berkshire, England, UK. March.

John Waters / Pair of Brown trout (Salmo trutta) spawning, with another male trying to fertilise eggs River Kennet, Berkshire, England, UK. February.

Cyril Ruoso / Common frogs (Rana temporaria) and frogspawn in pond, Yonne, Burgundy, France, February. Commended in the Reptiles, Amphibians and Fish Category of the Wildlife Photographer of the Year Awards competi...

John Waters / Pair of Sea lampreys (Petromyzon marinus) spawning, one attempting to move a rock, River Wye, UK, June.

John Waters / Timelapse Frogs (Rana temporaria) spawning in garden pond, Somerset, England, UK. March.

Wild Wonders of Europe / Widstrand / Humpback whale (Megaptera novaeangliae) tail fluke above water before diving, Senja, Troms County, Norway, Scandinavia, January. Cetaceans are attracted to this area to feed on the large numbers of sp...

Wild Wonders of Europe / Widstrand / Humpback whale (Megaptera novaeangliae) tail fluke above water before diving, Senja, Troms County, Norway, Scandinavia, January. Cetaceans are attracted to this area to feed on the large numbers of sp...

Wild Wonders of Europe / Widstrand / Orca / Killer whale (Orcinus orca) surfacing, Senja, Troms County, Norway, Scandinavia, January. Cetaceans are attracted to this area to feed on the large numbers of spawning Herring fish

Wild Wonders of Europe / Widstrand / Dorsal fin of Orca / Killer whale (Orcinus orca) surfacing, Senja, Troms County, Norway, Scandinavia, January. Cetaceans are attracted to this area to feed on the large numbers of spawning Herring fis...

Tony Wu / Twinspot snapper (Lutjanus bohar) engaged in a mass spawning aggregation early in the morning. Caroline Islands, Palau. April.

Tony Wu / Twinspot snapper (Lutjanus bohar) shoal rushing up to spawn, releasing a cloud of milky white sperm and eggs in the water column. Caroline Islands, Palau, November.

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 / Yellowbelly hamlets (Hypoplectrus aberrans) pair spawning at dusk (artifically backlit). Hamlets are hermaphroditic species. George Town, Grand Cayman, Cayman Islands. Caribbean Sea.

Brandon Cole / Sockeye salmon (Oncorhynchus nerka), male sockeye salmon fighting up a shallow stream on its migration to spawning beds. Adams River, British Columbia, Canada, October 2014

Brandon Cole / Sockeye salmon (Oncorhynchus nerka) from behind whilst on migration to spawning ground. Adams River, British Columbia, Canada, October 2014

John Waters / Underwater view of a group of Common toads (Bufo bufo) in a mating ball in a pond, Priddy, Somerset, England, UK, March.

John Waters / Underwater view of a group of Common toads (Bufo bufo) spawning in a pond, some in amplexus, with spawn, Priddy, Somerset, England, UK, March.

John Waters / Group of Common toads (Bufo bufo) in a mating ball in a pond, Priddy, Somerset, England, UK, March.

John Waters / Group of Common toads (Bufo bufo) in a mating ball in a pond, Priddy, Somerset, England, UK, March.

John Waters / Group of Common frogs (Rana temporaria) spawning in a garden pond, with floating spawn, Somerset, England, UK, March.

Alex Mustard / Portrait of pair of Bohar snappers (Lutjanus bohar) in their spawning aggregation. Shark Reef, Ras Mohammed Marine Park, Sinai, Egypt. Red Sea.

Alex Mustard / Portrait of Bohar snappers (Lutjanus bohar) in its spawning aggregation. Shark Reef, Ras Mohammed Marine Park, Sinai, Egypt. Red Sea.

Charlie Summers / Black Bear (Ursus americanus) hunting for spawning Salmon during low tide, Neets Creek estuary, Alaska, July.

Alex Mustard,Alex Mustard / A female (in front) and male Sockeye salmon (Oncorhynchus nerka) over eggs in their spawning river. Adams River, British Columbia, Canada, October.

Jurgen Freund,Jurgen Freund / Flexible Leather Coral (Sinularia flexibilis) spawning during the annual mass coral spawning event, in November, Great Barrier Reef, Queensland, Australia

Alex Mustard / Synchronous spawning of a mountainous star coral (Montastraea faveolata) at night. East End, Grand Cayman, Cayman Islands, British West Indies, Caribbean Sea.

Alex Mustard / Boulder star coral (Montastraea annularis) spawning at night with released bundles of eggs and sperm floating away in the water column, East End, Grand Cayman, Cayman Islands, British West Indies, Car...

Alex Mustard / A large colony of Mountainous star coral (Montastraea faveolata) spawning at night on a coral reef, showing the synchronous release of bundles of eggs and sperm, East End, Grand Cayman, Cayman Islands...

Michel Roggo / Grayling (Thymallus thymallus) on spawning ground. Lac de Fenetre, alpine lake, 2456 m above sea level, Canton of Valais, Switzerland, June.

Michel Roggo / Grayling (Thymallus thymallus) on spawning ground. Lac de Fenetre, alpine lake, 2456 m above sea level, Canton of Valais, Switzerland, June.

Michel Roggo / Sockeye / Red Salmon (Oncorhynchus nerka) on spawning migration; males surrounding a female. Adams River, British Columbia, Canada, October.

Michel Roggo / Sockeye / Red Salmon (Oncorhynchus nerka) on spawning migration. Adams River, British Columbia, Canada, October.

Michel Roggo / Sockeye / Red Salmon (Oncorhynchus nerka) on spawning migration. Adams River, British Columbia, Canada, October.

Michel Roggo / Sockeye / Red Salmon (Oncorhynchus nerka) on spawning migration. Adams River, British Columbia, Canada, October.

Michel Roggo / Sockeye / Red Salmon (Oncorhynchus nerka) on spawning migration. Adams River, British Columbia, Canada, October.