Mortgage-finance company Fannie Mae will send the U.S. Treasury $1.8 billion in June, after posting a first-quarter that declined sharply from a year earlier, thanks largely to a sizable derivative loss and a drop in credit-related income.

That payment brings the total amount returned to taxpayers to $138.2 billion. Fannie, along with Freddie Mac, was put into a conservatorship by the U.S. government in September 2008 after crisis-era losses. Fannie received $116.1 billion in bailout funds while Freddie received $71.3 billion in support.

The company said that its first-quarter net income was $1.9 billion, down from $5.3 billion in the same quarter of 2014. Analysts expected $2.6 billion.

Net interest income, which includes fees from backing mortgages, was $5.1 billion, up from $4.7 billion a year earlier. The increase was largely driven by guaranty fees.

Fannie said Thursday that an increasing portion of net interest income has been coming from guaranty fees, versus from interest income earned on the company's retained mortgage portfolio assets, and the company expects that guaranty fees will continue to account for an increasing portion of its net interest income.

Fee and other income dropped to $308 million from $4.4 billion in the first quarter of 2014. Credit-related income plunged to $60 million from $1 billion as the company booked a $473 million loss stemming from foreclosed properties.

Fair value losses helped offset gains in net interest income. Fannie reported derivative losses of $1.9 billion in the first quarter, up from $1.2 billion a year ago. Earlier this week, Freddie reported a $2.4 billion derivative loss. For accounting purposes, the companies mark derivatives to the market price, even as they carry many of hedged investments at cost. Because of that mismatch, derivatives can show a loss when rates fall, even though the effect should even out over time.

Fannie, along with Freddie, buys mortgages from lenders, wraps them into securities and then guarantees the loans in the event of default. Under the terms of their bailouts, the companies can't build capital buffers and instead send profits to the government. Legislators put the current structure in place with the idea that, by now, Congress would have overhauled the housing-finance system.

On Tuesday, the Federal Housing Finance Agency, which regulates Fannie and Freddie, said it is considering raising the salaries of the companies' chief executive officers, despite objections from the Treasury Department. Melvin Watt, director of the FHFA, cited CEO retention, succession plans and operational continuity in his decision to consider the pay raises.

Write to Lisa Beilfuss at lisa.beilfuss @wsj.com

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