Oil and gas group Ophir Energy was a high riser after announcing that its joint venture with BG Group found its fifth consecutive gas discovery in Tanzania with the Mzia-1 well in Block 1 showing "significant potential upside". Digital sports media company Perform Group jumped after announcing that it is to acquire Swiss firm RunningBall, a real-time sports data provider, for between €101-120m. Meanwhile, oil and gas engineering firm Lamprell has seen its share price plunge after it warned that its performance is being severely hampered by the paucity of specialised jack-up rig components. The group said it will most likely make a small loss in the first half of the year, though a recovery is expected in the second half. Provident Financial was also among the heaviest fallers early on after going ex-dividend. FTSE 250 - RisersOphir Energy (OPHR) 581.00p +12.82%Perform Group (PER) 329.00p +6.65%RPC Group (RPC) 370.90p +5.67%Ruspetro (RPO) 169.40p +5.22%Barratt Developments (BDEV) 124.00p +5.00%Persimmon (PSN) 574.50p +4.84%Dixons Retail (DXNS) 15.43p +4.26%Logica (LOG) 69.10p +4.07%Petropavlovsk (POG) 405.20p +3.76%Balfour Beatty (BBY) 268.00p +3.68%FTSE 250 - FallersLamprell (LAM) 122.10p -58.58%Aquarius Platinum Ltd. (AQP) 87.30p -6.88%Essar Energy (ESSR) 117.80p -5.99%Anglo Pacific Group (APF) 264.40p -4.93%Bwin.party Digital Entertainment (BPTY) 132.60p -4.47%Kentz Corporation Ltd. (KENZ) 381.20p -4.12%SDL (SDL) 671.00p -4.01%EnQuest (ENQ) 118.00p -3.91%Provident Financial (PFG) 1,116.00p -3.79%African Barrick Gold (ABG) 316.80p -3.47%NR