Old Gold, Australia's smallest credit union, has merged with First Option Credit Union, bringing the number of mutuals ADIs in Australia to 89.With 724 members, Old Gold has a tiny asset base of A$5 million.Formed in Hobart in the 1970s to cater to employees of Cadbury Australia, Old Gold never reached beyond its narrow industrial bond.Graeme Yeo, chair of the board of First Option Credit Union, wrote at its website that "as a standalone entity, OGCU lacked the resources required to provide its members with a comprehensive suite of products and services."He said that First Option "will be strengthened by this further diversification of our Member base whilst still retaining our industrial bond," which is in the gaming and energy sectors.The merger will lift the assets of First Option to around $170 million, in the middle of the rankings of the fast thinning ranks of credit unions.More than a quarter of remaining credit unions have assets of less than $100 million.