Owner Laskaridis told TradeWinds the 436,368-cbf Frio Athens (built 1988) was targeted by gunmen 55 miles from Bonny on 4 May.
The crew employed evasive manoeuvres as bullets hit the accommodation area.
There were no injuries to crew and the gunmen did not board.
Laskaridis said it would continue to trade in the region, but was requesting extra assistance from authorities - possibly an escort into Port Harcourt.
On the same day, the French-owned 3,650–teu CMA CGM Africa Four (built 2010) was targeted, but avoided the pirates by increasing speed.
It made it into Onne in Nigeria later that day.
Nine crew have been seized from two ships in the area in the last two weeks as pirate activity increases.
