Launceston Aquatic's Emily Mitchell set a massive personal best time and a new Tasmanian record for the girls' 13 years 200m backstroke on Wednesday to claim a bronze medal.

In the morning heats, the Scotch Oakburn student recorded what Swimming Tasmania described as a "huge PB" with a time of 2:24.67, breaking former clubmate Freya Jetson's state record of 2.26.93 to become the third fastest qualifier for the evening final.

Mitchell then easily beat her new PB and own record in the final, with a time of 2:22.97 in what the state sport's governing body called "sensational swimming".

Queensland's Claveria Johnson-Tiumalu won the race (2:20.32) and Sienna Shepherd, of Victoria, was second (2:22.55), just 0.42 of a second ahead of Mitchell.

Earlier in the meet, Hobart's Max Giuliani also claimed bronze and a new state record, in the boys' 15 years 100m freestyle (51.80). He had gone into the final as the fastest qualifier.

Twenty-five Tasmanians are taking part in the championships.

They started on Monday, and continue until Monday, April 22.

Distance swimmer Jardene Ralph, formerly of Launceston, but now training with Sandy Bay, won a bronze medal in the 19-20 years 1500m freestyle with a seven-second PB of 17:27.58 at the Australian swimming championships.

That meet, also in Adelaide, preceded the national age titles.

June 30: Regional short course championships, Launceston.