The old and the new of Australian swimming triumphed at the national championships when world champion Petria Thomas and unknown Cairns teenager Zoe Tonks snared gold medals.

Thomas swam her last race before packing her bags for hospital to have shoulder surgery, winning her sixth 50m butterfly title.

Tonks won the 200m backstroke gold at the Sydney Aquatic Centre, reducing her coach Glen Evans to tears.

"I got a bit emotional. I don't often cry but I did then," said Evans, who coached former world championship representative, Julie Majer.

"I'm going to start again. You don't get a 15-year-old up there every day, do you?"

Tonks, who had never contested a national open titles before, slashed about two seconds off her personal best this week to win the gold in 2m14.30s.

She was the youngest swimmer in Friday night's final and will be the baby of the Australian team to contest the Barcelona world titles in July.

"I'm absolutely thrilled. It sort of hasn't really hit me yet," she said after the race.

Backstroke swimming obviously runs in the family with her 14-year-old cousin Alexander Ross also qualifying for the semi-final of the men's 200m backstroke.

As Thomas prepares for surgery on her left shoulder next Tuesday, Tonks will be on her way to Indianapolis with the rest of the Australian team for the April 6 "Duel in the Pool" meet against the United States - her first international swimming competition.

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