Shares in Carnival fell back after the cruise ship operator announced a fall in earnings in the second quarter and failed to impress the market with third quarter guidance.Pre-tax income in the three months to May 31 fell to $251m from $270m over the same period the previous year as revenues climbed to $3.20bn from $2.95bn.Carnival said that revenues were boosted by an 8% increase in passenger capacity.'Considering recent global economic concerns and other world events our advance bookings are holding up reasonably well and remain in line with our expectations,' said chief executive and chairman Micky Arison. 'We believe this will lead to earnings growth in both the third and fourth quarters.'Carnival said it expects third quarter earnings to be between $1.43 and $1.47, above $1.33 over the same period last year, but below some analysts' estimates.