Bishop was a regular at the Ospreys before fracturing his kneecap
David Bishop, Filipo Levi, Leigh Bevan and Michael Collins have left the Ospreys at the end of their contracts.
Centre Bishop is the most surprising, the talented former Celtic Warriors centre, 25, having had his development blighted by a serious knee injury.
Winger Bevan and lock Collins, both 22, have each played just twice for the region, while the Ospreys confirm that Samoan captain Levi joins Newcastle.
"This is always a difficult time," said Ospreys boss Andrew Hore.
"Decisions have to be made for the good of both the region, and the individual players.
"I would like to pass on the best wishes of everybody at the Ospreys to the four players who are leaving us, we certainly wish them all the best for their future rugby careers, wherever it may take them.
"The attitude and commitment of all the players has always been unquestionable and they have been good servants to the region during their time as an Osprey."
Bishop, the brother of Ospreys and Wales centre Andrew, was a regular in his first season at the Liberty Stadium region in 2004/5.
He suffered a fractured kneecap in a Magners League game at Munster early the following season, an injury that required two operations and ultimately kept him out of Ospreys reckoning for three whole years.
He returned to regional action in September 2008 against Glasgow, one of six appearances last season.
Meanwhile, Neath and Wales Sevens back-rower Lee Beach, 26, has joined London Welsh.
The ambitious Richmond-based club have recruited former England hooker Phil Greening as assistant coach.