Bluespotted Boxfish (Ostracion immaculatum) ハコフグ also Japanese Boxfish and Blackspotted boxfish
The male Bluespotted Boxfish has a blue back. This one will get darker and larger. Enoshima
The female Bluespotted Boxfish has a lighter back. Enoshima
A young male Bluespotted Boxfish. Enoshima
A juvenile Bluespotted Boxfish has blue spots. Even younger ones are yellow with black spots. Later they have balck and blue spots. eventually the spots there are blue spots with tiny black spots. This fish is sometimes called Ostracion immaculatus which is incorrect. Enoshima