A fry
Newly hatched insects are generally called crawlers.
A newly born or hatched fish is a fry.
alevin
Newly-hatched fish are known as "fry." Other names include hatchlings and fingerlings.
A chick?
Snakelet, neonate (a newly-born snake), hatchling (a newly-hatched snake)
A newly hatched cockroach is called a nymph.
A newly born snake is called a Snakelet Neonate while a newly hatched snake is called a hatchling
The word FRY is used for small fish, especially young, recently hatched fish.Source: Thefreedictionary.com
The word krill comes from a Norwegian word meaning freshly hatched fish.
The official name for them are Neon Tetras.
There is no particular name for a baby tuatara. Newly hatched tuatara are called hatchlings, and tuatara that are not yet adult are simply called juvenile tuatara.