Newly hatched insects are generally called crawlers.
Fry
A fry
A newly born or hatched fish is a fry.
alevin
Newly hatched sultan fish are born with very small, soft scales. They are also much smaller than adult fish. Despite their small size, newly hatched sultan fish are able to feed themselves.
Newly-hatched fish are known as "fry." Other names include hatchlings and fingerlings.
alevin
Fry [1913 Webster] Alevin
Fry. Or alevin.
A Baby Fish is called a Fry, a fingerling, or a guppy.
A chick?
An alevin is a newly hatched fish, especially a salmon.
Newly hatched ducklings actually do not have feathers.