Ingo Arndt / Sea trout (Salmo trutta trutta) alevin just hatched with full yolk sac, Europe

Solvin Zankl / As soon as it entered the water the young Olive ridley sea turtle (Lepidochelys olivacea) struggles against the swell to swim away from the coast. The swimming frenzy lasts for approximately 48 hours...

Ingo Arndt / Amu-Darya Trout (Salmo trutta trutta) alevin freshly hatched with full yolk sac, Europe

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...

Jeff Rotman / Newborn Spiny dogfish {Squalus acanthias} with yolk sac attached, Atlantic, USA

Tony Wu / Flamboyant cuttlefish (Metasepia pfefferi) close up of egg with the developing juvenile attached to its yolk sac and visible inside the egg, Lembeh Strait, North Sulawesi, Indonesia

Michel Roggo / Atlantic Salmon (Salmo salar) young fry with yolk sac almost empty. Allier river, France, in hatchery of the Research Station Petite Camargue Alsacienne, France, February. Captive. Sequence 5 of 5.

Michel Roggo / Atlantic salmon (Salmo salar) recently hatched fry with yolk sac. Allier river, France, in hatchery of the Research Station Petite Camargue Alsacienne, France, February. Sequence 4 of 5.

Solvin Zankl / As soon as it enters the water the young Olive sea turtle (Lepidochelys olivacea) struggles against the swell to swim away from the coast. Pacific coast, Costa Rica, October. ^^^This swimming frenzy...

Solvin Zankl / As soon as it enters the water the young Olive sea turtle (Lepidochelys olivacea) struggles against the swell to swim away from the coast. Pacific coast, Costa Rica, October ^^^ This swimming frenzy...

Jeff Rotman / Newborn Spiny Pygmy Shark (Squaliolus laticaudus) with yolk sac still attached held in hand, Israel, Mediterranean Sea.

Ingo Arndt / Amu-Darya Trout (Salmo trutta trutta) alevin freshly hatched with full yolk sac, Europe