The business of minding investor's funds has been a nice earner for custodians in the Australian market over the past six months. The Australian Custodial Services Association reported yesterday that total assets under custody for Australian investors increased by 8.3 per cent to A$2.3 trillion in the six months to December.National Australia Bank's NAB Asset Servicing is the biggest player in the market, with $632 billion of assets under custody. NAB increased its assets under custody by 11.4 per cent over the six months to December.Other leading custodians include JP Morgan, with $419 billion of assets under custody, BNP Paribas ($305 billion of assets), Citigroup, ($254 billion of assets) and State Street ($199 billion of assets).Citigroup recorded the strongest growth over the six months to December, increasing its assets under custody by 19.4 per cent, while BNP Paribas lost 2.6 per cent of its assets.The $2.3 trillion of assets under custody is made up of $1.7 trillion of Australian assets and $650 billion of non-Australian assets held for Australian investors. In addition, custodians held $959 million of Australian assets for foreign investors.ACSA chair David Braga said the data demonstrated the stability of the sector. "The industry's expectation is that we will see similar levels of steady growth this year," Braga said in a statement.