David Davies broke two British records in Rome but could not claim a medal
Wales' David Davies finished sixth in the 1500m World Championships freestyle final in Rome.
The 24-year-old's time of 14 minutes 57.03 seconds was 20 seconds behind winner Oussama Mellouli of Tunisia.
City of Cardiff swimmer Thomas Haffield set a Commonwealth record of 4:11.32 in qualifying fifth for the 400m individual medley final.
But the 21-year-old Welshman's 4:13.63 in the final left him joint last, Ryan Lochte of the USA winning in 4:07.01.
Davies, who holds the national 1500m freestyle record of 14:45.95, broke two British records in Italy.
I knew this week was going to be tough and it was just one race too many
He lowered the 800m freestyle mark twice (to 7:44.32) as he finished fifth in a race that saw the world record lowered by six seconds by China's Lin Zhang.
The Barry-born swimmer also helped the men's 4x200m freestyle relay team to the final but was left out when the team lowered the British record in another record-breaking final as Great Britain finished seventh.
Davies, who also finished last in the 400m freestyle final, was in third place in the 1500m until the 600m mark when he dropped to fourth and was never in contention after that and admitted he had nothing in the tank.
"I thought 'Oh, my God, I've run out of fuel'," said the Welshman.
"At the halfway point when you know you have half to go it is the worse feeling in swimming.
"I struggled in the heat [Saturday], it was a tough, tough swim.
"I tried to recover as best I could and until halfway I felt ok but then ran out of gas.
"I knew this week was going to be tough and it was just one race too many."
Gold-winner Mellouli was almost three seconds outside Grant Hackett's iconic 2001 world-record mark.
Davies, though, predicted the record would go despite the return to suits, although he admitted he was glad it remained, adding he would text Hackett to congratulate him on retaining it.
Davies has toyed with the idea of specialising in the 10km open water for the 2012 Olympics in London if that offers him a better chance of a gold medal.
But he is still confident that he can become the world's best in his favoured discipline of 1500m.
Davies has won three bronze medals in the 1500m freestyle at Olympic and world level as well as a silver in the 10km open water at the last Olympic Games in Beijing.