FRANKFURT, April 9 - The European Central Bank said on Wednesday foreign currency reserves of the euro zone central banks in the week ending April 4 fell by a net 7.7 billion euros, mainly due to a quarterly balance sheet revaluation. Customer and portfolio transactions in the reporting week resulted in an increase of 0.3 billion euros, the bank said in its regular weekly consolidated financial statement. The net position of the ECB and euro zone central banks in foreign exchange reserves totalled 211.3 billion euros at the end of the reporting week, the ECB said. Gold holdings were unchanged, but the quarterly revaluation caused them to decline by 7.586 billion euros to 122.728 billion euros. The ECB every quarter revalues its foreign exchange, gold and securities holdings at market rates.//