According to the portal, the incident occurred at 12:22 GMT, 108 nautical miles northwest of Sao Tome.
The Maritime Bulletin portal notes that a Greek company, Lotus Shipping, owns the Panama-flagged vessel.
At the time of the attack, the fishing vessel Lianpengyu was nearby. It was seized by pirates on February 7 and has been under their control since that time, according to reports.
The Gulf of Guinea has overtaken the Somalian Horn of Africa as the most pirate-heavy waters, with an uptick of attacks over the past two years.