MIAMI, June 22 (Reuters) - The U.S. Coast Guard has ended its search for a Brazilian-born multimillionaire whose fishing boat washed up on a south Florida beach earlier this week.

The Coast Guard said it called off the search for Guma Aguiar, the 35-year-old founder of a Texas oil and gas company that he sold for a reported $2.55 billion in 2006, late Thursday evening.

The air-and-sea search spanned a 1,523-square-mile (3,944 sq km) area, roughly the size of Rhode Island. But it yielded no trace of Aguiar, whose 31-foot (9.4 meter) fishing boat, the T.T. Zion, washed ashore on a Fort Lauderdale beach before dawn Wednesday with its navigation lights on and twin outboard engines still running.

Aguiar, a resident of Fort Lauderdale, had turned to Jewish philanthropy since the sale of his energy company Leor Energy, according to local media reports.

Fort Lauderdale Police quoted his wife, Jamie Aguiar, as saying a family employee told her he went out on his boat about 7:30 p.m. EDT (2330 GMT) on Tuesday and had not been seen since.

Aguiar's mother, Ellen Aguiar, filed documents in Broward County court seeking to become a conservator or temporary custodian of his nearly $100 million fortune, according to the Sun Sentinel newspaper.

The petition, which says Aguiar's disappearance may have been due to "mental derangement," claims that he suffered from "severe bipolar disorder."

Police were unavailable for immediate comment on Friday. But in her petition, Ellen Aguiar said his cellphone and wallet were found on the fishing boat. (Reporting By Tom Brown; Editing by Bill Trott)