Sockeye salmon alevin, Katmai National Park & Preserve, 2015.

These sockeye salmon (Oncorhynchus nerka) young are called 'alevin'. You can see that they even still have a yolk sac attached to their bodies! This sac contains protein, sugar, minerals and vitamins that the alevin live on for about a month, after which time they will emerge from the gravel and begin to hunt for food. When the sac is absorbed and alevin leave the gravel they become known as 'fry'. Alevin that leave the gravel before the yolk sac is completely absorbed are commonly called 'bottom-up fry'. Usually, however, salmon alevin will hide in these gravel nests for weeks after birth. As streams and lakes in Katmai thaw their winter ice cover, alevin venture out so they can grow into beautiful salmon fry and eventually become adults. From this point on, their lives are fraught with danger! Photo from wikipedia commons, by OpenCage.