Retail sector industry fund REST is Australia's fastest-growing superannuation fund, according to the latest report from Tria Investment Partners.

The fund grew by 0.41 per cent to $14.6 billion in the year to June 2009.

In the same period, Sunsuper and AGEST were the next two fastest-growing funds, expanding 0.25 per cent and 0.15 per cent respectively. 

Growth of these funds was related to their history and demographics, Tria Investment Partners managing partner Andrew Baker said.

"REST's growth in 2009 was their best result in years. They are located in a good industry [retail sector] and Australian retail continued to do well through the GFC (global financial crisis)," Baker said.

"Sunsuper's growth is attributed to its Queensland location and past success in winning consolidation and tender business.

"AGEST benefits from the perpetual growth in public servants."

MTAA Super, timber industry fund First Super and Maritime Super experienced the fastest losses in terms of market share.

"Funds taking losses in market share are generally funds located in slow growth industries, which is certainly the case with First and Maritime," Baker said.

"MTAA and Westscheme are normally among the fast growers. They appear in the losses section this year because of the impact of large devaluations on their investment portfolios."

He said there would be more fund mergers, however, the top six funds - AustralianSuper, UniSuper, REST, HESTA, Sunsuper and Cbus - would be "under no pressure".

Other superannuation funds would have to assess whether they could maintain their competitiveness in the future, he said. 

"These funds will need to be very watchful of their ability to deliver competitive performance and services while preventing cost ratios from rising far," he said.

"Some of them will also be keen to seek additional scale, as we have recently seen with the recent merger announcement of Equipsuper and Vision Super."