Online brokerage TD Ameritrade says trading activity declined in April, but the amount of client assets the firm holds continued to grow.

The Omaha company said Tuesday that it handled an average of 402,000 trades per day in April. That's down 3 percent from March and down 6 percent from April 2010, but trading normally declines heading into slower summer trading.

Ameritrade says it held $423 billion in total client assets at the end of April. That's 3 percent higher than at the end of March and 21 percent higher than last April.

Ameritrade generates revenue from commissions it charges investors on trades and from asset-based fees and interest it gets on the assets it holds.