The Serbian native landed in New Zealand last month to become the organisation's first full-time coach.
It is hoped Radjen's appointment will raise the standards of Otago water polo teams and attract new players to the sport, Water Polo Otago chairwoman Alisha Clark said.
Finding a coach with with Radjen's expertise and passion for the sport came through an unlikely avenue.
Clark sent a Facebook message to a friend who was attending a water polo training camp in Serbia, where Radjen was coaching.
''A friend of mine was at a camp that Nemo was running.''
''I cheekily said 'if anyone wants to come back to Dunedin let me know' and then he came back to me and said I had found someone.''
Radjen and Clark also connected via Facebook before arrangements were made with Water Polo Otago for the coach's appointment.
The 26-year-old comes to New Zealand following an extensive water polo coaching career across Europe.
''I did something like this in Israel for 2½ years - from there I came here,'' Radjen said.
''I started there in a club and went on to the national [team] and then basically I left everything and came here.''
''Before then I started coaching in Belgrade in 2012.''
How Radjen and his two-time Olympic bronze medal-winning brother Nikola took up water polo could be described as as much of a chance opportunity as his landing his new job.
At just 5 years old the Serbian brothers ditched their hockey sticks for the pool.
''Me and my brother, we started playing hockey. At that time in my country the equipment was very expensive and [you] are growing.
''So my mother told us you [only] need a swimming suit and towel to go to the pool so we starting playing water polo.''
Since then water polo has been Radjen's passion.
''All of my life is water polo.''
''I have dedicated myself and all of my family just for this work.
''Water polo is a great sport to develop your body to the maximum.''
Otago has been in the bottom half of the nation's water polo ranks recently, but the province's talent was on show when the under-21 men's side was fourth at last year's national championships, Clark said.
Otago has the major disadvantage of not having regular competition within its own region.
''Auckland clubs, for example, are playing games against each other every week and we do not have that.''
''We have to travel to play - we have competitions against Canterbury and Southland but that is only four times a year.''
It is hoped Otago sides will be able to lift themselves into the top bracket of the national provincial ranks with the help of Radjen's technical coaching.
It is also hoped strengthening the Otago water polo scene could attract more players which would help with internal competition and practice.
The new season starts on February 11 with registration at Moana Pool.
The only prerequisite for anyone interested in playing is to be able to swim.
Prospective players will be given all of the coaching and technical advice they need, Clark said.
