Cape Town - Blue Bulls forward Derick Kuün has shocked the Pretoria-based union by announcing his retirement from rugby with immediate effect.Kuün - who has won three Super Rugby crowns with the Bulls, as well as winners medals in the Currie Cup and Vodacom Cup - cited business reasons for his decision.“It is with a heavy heart that I announce my retirement, but a couple of business opportunities came along and I have to act on them immediately. I will join a family business,” Kuün told the Bulls website.The hooker/loose forward recently played his 100th provincial match for the Blue Bulls after making his debut against Border in 2004. He also captained the Blue Bulls at all junior and senior levels, as he did with the SA Schools side in 2002. He played at national level for the Springboks Sevens team as well as the national u19 & u21 sides, representing his country at the IRB Junior World Cups in 2003, 2004 and 2005. Kuün thanked the Bulls union for its contribution to his career. "I would like to thank the union and company for the opportunity of being part of the Blue Bulls and Bulls family for nine years of my life. I learned a lot about life in this time. I also appreciate the amount of time that was invested in me from management level," said Kuün.He also thank his fellow players and fans for their support over the years."I can only say thanks to all those players that I played with during the years. There were great times and bad times and all of that formed me to what I am today," Kuun told SAPA."I will miss my rugby friends greatly, as we have bonded into a special group. To the fans, a special word of thanks. Your support is very important and there is no greater feeling running out to a packed Loftus Versfeld. My blood will always be Blue."Head of Rugby at the Blue Bulls, Heyneke Meyer, says it is a sad day for Bulls and Blue Bulls rugby.“Derick was a true team man and a great stalwart for the union. He is the perfect example of the type of player we want to represent the Blue Bulls and Bulls. He proved himself to be a great leader, played with courage and skill and always gave everything he had. He also had an uncanny understanding of team dynamics and because of that, has proved to be an outstanding leader,” said Meyer.