ONDON, June 23 — Playing the title role in "Ariadne auf Naxos" at its opening on Tuesday, the German soprano Anne Schwanewilms certainly looked slinky in her swirling black dress with its skinny little straps. But it was not clear whether her pleasing litheness was essential to the role, as the Royal Opera had contended when it removed Deborah Voigt from the production because she was too heavy.

It was not so much that anyone objected to the regal Ms. Schwanewilms, who was applauded at Covent Garden with a sincere warmth and enthusiasm that almost seemed to take her aback. Nor were there any complaints about the elegant modern-dress production, directed by Christof Loy and designed by Herbert Murauer, which opened to ecstatic reviews in September 2002 and has been revived this season with a new cast. The production calls for some fairly vigorous staging and much wearing of skimpy garments: in addition to Ariadne's A-line slip dress, there is a short, low-cut wisp of a frock worn with high-heeled ankle boots by the frisky Zerbinetta (Diana Damrau). While she doesn't cavort as much as Ms. Damrau, who in the prologue flings off her top and is left wearing just a pair of tight jeans and a bra, Ms. Schwanewilms does spend a fair amount of time stretched out onstage, riven by grief, her dress draped fetchingly around her sinuous form.
		Anne Schwanewilms, who replaced Deborah Voigt in "Ariadne."

But operagoers interviewed after the performance said that they could not understand why Ms. Voigt had been jettisoned when, in the words of one, "even if Ariadne had been fat, she would have been fine."

That is not what the casting director, Peter Katona, said in March when the news emerged that Ms. Voigt's contract had been canceled about five years after she was recruited to play Ariadne.

"Although Ms. Voigt is a wonderful singer, the costume and type of production made it not such a fortunate suggestion that she be in it," he told The Sunday Telegraph of London. "In making these kinds of decisions it is not just a question of how someone looks; it is also how they move on stage. We had to make it theatrically convincing."

Ms. Voigt, who as one of opera's leading dramatic sopranos has made "Ariadne" one of her signature roles, explained then that she had been told that because she was too heavy for the cocktail dress envisioned for the production she — not the dress — would have to go.

But why not just put Ms. Voigt in a sumptuous evening gown and let her stay? "If she's a good singer and actress, she should have been kept in," Paulo Pacheco, an audience member from Brazil, said. "I've seen Butterflies who were a lot bigger than Pinkertons," he said, referring to characters in "Madama Butterfly." "It might look strange, but the important thing is the singing and the acting."

Myra van Hus, another Covent Garden operagoer, said she too had seen "quite a few productions with enormous women and small men" and that it had never bothered her because "the music and singing are what matter in opera."

In addition, she noted, the tenor Richard Margison, who plays Bacchus in "Ariadne," is a bit short and portly, lending a certain incongruity to his status as romantic lead and touching off some creative staging wherein he and Ms. Schwanewilms generally stand far away from each other, embracing only when she is safely sitting down.

Ms. van Hus said that the trend toward slighter female opera singers was an unwelcome example of values migrating from the film industry, where, she said, "the popular type of actresses are so skinny."

"Let them stick to film," she said. "I'm puzzled that it's entering into the world of opera, and I hope people are fighting back."

Jorgen Schiott, another audience member, said that "while I'm not unhappy, I would have loved seeing Voigt in the role." Although if Ms. Voigt had kept the job, Mr. Schiott added, "I don't think Ariadne would have been lying on the floor quite so much."