Self-storage firm Big Yellow said it delivered a "solid trading performance" in its fiscal first quarter with both occupancy and rental yields up over last year.Occupancy at its 55 wholly-owned stores in the UK grew by 125,000 square foot over last year in the three months to June 30th with move-ins up 6% on a like-for-like basis.Net rent per square foot was £26.37, 5.2% higher than a year ago.This helped revenue from the 55 stores increase 11% to £18.6m.Occupancy, rents and revenues also increased in the 12 Big Yellow Partnership stores, in which it owns a 33.3% stake, and the 10 Armadillo stores in Australia (20% ownership)."We continue to see improving demand and have delivered a solid performance in the quarter," said Chief Executive James Gibson."The first quarter is historically our strongest quarter, but we would expect to deliver further occupancy gains in the second quarter," he said.While occupancy growth was slightly softer than the modest gain on the previous year that analysts at Liberum had expected, pricing was ahead of expectations meaning that overall revenue growth of is in line with Net Operating Income forecasts.The stock was up 3% at 504.98p by 12:03 on Wednesday.BC