They appear as large, bright orange puffer fish. Their only attack is jumping at the player, dealing minimal damage with their spikes. When damaged themselves, they try to get away by flopping around on the floor.
They have extremely low health, but incredible defense - so much that it renders most weapon attacks to a minimal damage.
During Raid Mode, they tend to appear in optional areas. Upon defeat they will reward the player with a Weapon Case, which has a high probability of containing a stronger weapon.
Due to their appearance being exclusive to Raid Mode it's likely they aren't treated as a canon enemy. Interestingly they are treated as Ghiozzo's on the 3DS release of Revelations.
The RE.net description describes the Aculeozzo as "a variety of Ghiozzo resembling a puffer fish. Although the Aculeozzo is missing its cousin's sharp fangs, it can leap incredible distances, far more than its appearance would suggest".
After defeating original Norman on the bonus stage "Ghost Ship", player(s) will encounter giant Aculeozzo of level 60 along with other Ghiozzo's.
The Aculeozzo's high defense means that killing one can deplete your ammo reserves. The shock grenade, however, does significant damage. With a well placed throw the blowfish can be killed with a single shock grenade. As they aren't particularly dangerous, using the knife to attack is also a good option to conserve ammo.