With both already having claimed two medals, each were able to add another to their totals.
Roberts completed the trifecta, winning gold in the 400m freestyle to go alongside his silver and bronze from the first two days of competition.
In a tight race, Roberts was able to lead Australia’s Ethan Owens from start to finish, to win in a time of three minutes and 56 seconds, one second ahead of Owens.
Meanwhile, Kirsten Marsters-Fisher added another Pacific medal to her tally, this time picking up a silver in the 50m breaststroke, finishing again in fifth place with a time of 35.44.
The Pacific medals are handed out at the event for the top three competitors in each race from the Pacific Islands.
Other Cook Islands swimmers also in action included Tiernan Keane, who finished fourth in the ‘B’ final of the 100m butterfly with a time of 1.02.33, and Bede Aitu, who competed in the ‘B’ final of the 50m breaststroke, coming in sixth place with a time of 32.56.
The competition is being held at the Turama Aquatic Centre in Port Moresby, with the final night of pool competition tonight (CI time), before the open-water 10km swim tomorrow.