Opera / Bizet's Pearl Fisher all at sea: Opera: Nick Kimberley on The Pearl Fishers at the Coliseum and La boheme at the Barbican

Traditionally, opera in concert performance rescues pieces deemed unworkable in the opera house, but there's an emerging tendency to present repertoire operas in concert, as if to rescue them from directorial whimsy. I think opera belongs in the theatre, but I may have to change my mind, having just seen an opera staged with so little theatricality that a concert performance might be preferable, and a concert performance which subverted every decorum of the concert platform.

Sri Lanka, as we know it, may not be the Ceylon of Bizet's The Pearl Fishers, but that needn't be a problem. Sadly, it is for Philip Prowse's 1987 English National Opera production, back at London's Coliseum. Prowse seems to find Bizet's orientalism intractable, and his staging - which he also designed - presents a kind of Kensington Market vision, all incense and acrobats, confetti and strobes. Unable to locate the drama, he brings on supernumeraries to wheel and whirl. His set is dominated by a raised platform, forcing detours on the chorus, and pushing the singers downstage, where they fail to interact. As old friends Zurga (Jonathan Summers) and Nadir (John Hudson) are reunited, they hover distantly, as if waiting to be introduced.

It is all frustratingly untheatrical, although the musical performances are creditable. Summers' tone is rather colourless, but he projects a feral intensity; Hudson, taxed by Bizet's penchant for high tenor, sings vigorously. The most accomplished performer is Gillian Webster, her Leila only occasionally blemished by some pinched notes. Alexander Sander's carefully paced and focused conducting can't energise this depressing production of a work destined to remain peripheral.

At the Barbican, Michael Tilson Thomas conducted the London Symphony Orchestra and a starry cast in two concert performances of Puccini's La boheme. These were not formal concert performances, but fully enacted; exits and entrances observed, every gesture gesticulated, and more besides. As Musetta (Nancy Gustafson) enters from the auditorium, she kisses sundry members of the audience; and when the Cafe Momus scene ends, Tilson Thomas produces the bill which appalls Alcindoro (Alan Ewing). The singers' evident enjoyment was infectious. What in the opera house may appear conventionalised gesture, here became vivid theatre; and the Bohemian frolics were less tiresome because the context allowed less room for picturesque detail.

A superb cast responded well to Tilson Thomas's impassioned coaxing. Only Francisco Araiza, perhaps stale after playing in Rigoletto last month, sounded strained, the voice disappointingly harsh. Hampson was larger than life, and Gustafson believably flirty; and there were thrilling performances from two London debutantes. Simone Alberghini's Colline was deeply felt, resonantly sung, the fulsome bass remarkable in a 20-year-old; while Barbara Frittoli's Mimi, fully characterised both vocally and physically, brought the house down. She pulls the line around a little, but only to make it work for her. Odd moments of spreading tone could be put down to the thrill of the moment, for Frittoli seemed genuinely moved. A soprano to watch out for: if we get the chance. Only 26, Frittoli is already hooked into the international circuit where the Mutis and Abbados are sure to keep her busy.

'The Pearl Fishers' runs in repertory to 28 April