Northern Ireland swimmer Sycerika McMahon finished 24th in her opening event at the World Championships in Shanghai on Sunday.
McMahon, who won two golds and a bronze at the recent European Junior Championships, clocked 4:16.44 in the 400m freestyle heats.
She will be in action in several other events in China, including Monday's 100m breaststroke heats.
Belfast woman Melanie Nocher goes in the 100m backstroke heats on Monday.
Ireland's top swimmer Grainne Murphy will be in action in the 1500m freestyle on Monday - the event where she took silver at last year's European Long Course Championships.
The Wexford woman also won two medals at last year's European Short Course Championships and has developed into a world-class competitor.
Ireland's Barry Murphy had a disappointing swim in the 100m breaststroke heats on Monday.
His time of 1:02.50 was almost two seconds slower than his personal best set earlier this year.
Ireland's National Performance Director Peter Banks described McMahon's swim as a "postive start to the championships" for the Portaferry youngster.