Newly hatched insects are generally called crawlers.
A fry
A newly born or hatched fish is a fry.
alevin
Newly-hatched fish are known as "fry." Other names include hatchlings and fingerlings.
alevin
Fry [1913 Webster] Alevin
Fry. Or alevin.
Newly hatched sultan fish are typically small in size and have translucent bodies with underdeveloped fins. They rely on yolk sacs for nutrition initially and are vulnerable to predation in the wild. They often stay close to cover and shoal together for protection.
A Baby Fish is called a Fry, a fingerling, or a guppy.
A chick?
To be correct. Fish ova (eggs) do not actually "hatch" they 'develop'. A fish egg that has developed sufficiently for it to be recognised as a fish is called a "Fry"
An alevin is a newly hatched fish, especially a salmon.