The business of managing money can be extremely lucrative, and investors in Affiliated Managers Group (NYSE:AMG) have enjoyed the fruits of a long bull market in stocks. Recently, though, fears of a potential end to the long-lived advance in the market have sent shares of asset managers down sharply. Even industry giant BlackRock (NYSE:BLK) has been vulnerable, and coming into Affiliated Managers Group's fourth-quarter financial report, its investors also had concerns about its ability to weather a market storm. For now, Affiliated Managers Group has been able to hold its own, but more difficult times could lie ahead. Let's take a closer look at how Affiliated Managers Group did and what's ahead for the asset manager going forward.

Feeling the pinch of a tough market
Affiliated Managers Group's fourth-quarter results were mixed, with poor top-line performance but a slight beat on the bottom line. Revenue plunged 8% to $589.8 million, roughly double the rate of revenue declines that most investors were prepared to see. Even with the shortfall in sales, Affiliated Managers Group did its best to preserve its profitability. GAAP net income fell 13% to $172.6 million, but the company's preferred measure of economic earnings climbed slightly to $3.61 per share, topping the consensus forecast by a penny.

Looking more closely at the numbers, it's clear that the volatile market has had an impact on Affiliated Managers Group's business. Clients moved about $6.8 billion in cash out of the company's management, with all of the declines stemming from the mutual fund area of the business. Interestingly, market changes actually helped the company's assets under management in the fourth quarter, adding $12.2 billion and helping to offset $3.2 billion in foreign exchange-related declines. Overall, Affiliated Managers Group had $611.3 billion in assets under management at the end of 2015, up 3% from the end of September but down about 1.5% from year-end 2014.

Affiliated Managers Group has done good work to keep its bottom line healthy. Even in the backdrop of falling revenue, the manager cut its compensation costs by more than 9%, and a 10% cut in general overhead expenses also helped to limit the drop in operating income.

CEO Sean Healey was happy with the way that the asset manager performed during the quarter. "Against a challenging market backdrop in the second half of the year," Healey said, "our results reflect the diversity of our business and the successful execution of our growth strategy, including the long-term investment outperformance of our Affiliates and significant deployment of capital through our new investments strategy." That's the same strategy that peer BlackRock has used, with the company offering ETFs of all types as well as traditional BlackRock mutual funds and other vehicles for asset management.

Can AMG get its stock groove back?
Healey was also happy that all of the cash outflows came from the mutual fund side of the business. The CEO described the moves as stemming from "broader industry trends and one-off events." He pointed to the resiliency of the company's institutional and high net worth clients, who largely stayed the course during the turbulent markets in the second half of 2015.

Affiliated Managers Group has also continued looking for ways to keep growing. During 2015, the company added several traditional, alternative, and wealth management partners. The most recent announcement will add Asian private equity company Baring Asia to the mix, further deepening what is already an impressive lineup.

Still, the big concern that some have about the company stems from the closure of the Third Avenue Focused Credit Fund. Affiliated Managers Group owns a majority stake in Third Avenue Management, but AMG has said that it has no legal exposure to the Focused Credit fund's collapse. Indeed, the company says that withdrawals have started to moderate in the wake of the high-yield bond fund's December debacle, which stemmed from a loss of shareholder confidence following sharp losses due to the fund's high concentration in energy-company debt. But with index-driven alternatives from BlackRock and other managers available, Affiliated Managers Group has to control reputational damage to prevent further outflows.

Affiliated Managers Group shares didn't react positively to the earnings release, falling 5% in the first hour of trading following the announcement. Until markets calm down, it's likely that AMG stock will remain under pressure for the foreseeable future.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.