It's only fitting that TD AMERITRADE (NASDAQ:AMTD) reports its fiscal first-quarter results on the same day that Barack Obama is sworn in as President. After all, one campaigned on the "change you can believe in" slogan, while the other thrives in times of change.

TD AMERITRADE made the most of the past few months of market volatility. Average daily client trades clocked in at a brisk 357,294, 15% higher than last year's showing. Investors hungry to play the market's volatility led to a 10% spike in transaction-based revenue.

Unfortunately, net revenue itself fell by 5% to $610.7 million, as asset-based revenue surrendered far more than the gains on the transaction-based side. You can lay the blame on a sharp plunge in interest revenue during the quarter, as gun-shy clients avoided trading on margin, despite the temptation of lower interest rates.

Stack up TD AMERITRADE's report against rival Charles Schwab's (NASDAQ:SCHW) numbers from last week, and you'll see two companies that posted identical 5% dips in net revenue. However, while Schwab managed to post a slight uptick on the bottom line, TD AMERITRADE's profit of $0.31 a share fell well short of last year's $0.40-a-share showing.

Folks are still flocking to TD AMERITRADE, though. The company attracted $7.8 billion in net new assets during the quarter. The discount broker's asset base will get even stronger when it completes its purchase of thinkorswim Group (NASDAQ:SWIM), doubling the company's exposure to the options-trading niche where companies like optionsXpress (NASDAQ:OXPS) are feasting.

TD AMERITRADE nailed Wall Street's bottom-line expectations, but it's taking a cautious stance when it comes to its near-term outlook. The broker is looking to earn between $0.90 a share to $1.15 a share this fiscal year. The new range is well below the original net-income-per-share guidance of $1.10 to $1.42 that the company issued three months ago.

We'll have a clearer picture on the discount brokerage space when E*Trade (NASDAQ:ETFC) reports its quarterly results a week from today, but do we really need to wait? Schwab and TD AMERITRADE provide a pretty complete snapshot of an industry that is proving resilient in terms of trading activity, but problematic when it comes to interest revenue. With plunging interest rates fueling speculation that money market funds will have to cut expense ratios to attract deposits, let's hope that the "change you can believe in" isn't referring to the pocket-change yields that clients may decide to abandon.

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Longtime Fool contributor Rick Munarriz has been trading exclusively through discount brokers since 1990 but he does not own shares in any of the companies in this story. He is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early. The Fool has a disclosure policy.