Johnstone set a record of 31.78 secs in the morning heats of the 50m breatstroke, and went even faster with a time of 31.69 secs in winning gold in the final. The event is not part of the Olympic programme.
Meanwhile, Aberdonian David Carry qualified for his third successive Olympics. The 30-year-old won the 400m freestyle in a personal best 3:46.86.
Advertisement
Hide AdAdvertisement
Hide AdCarry, who will be the oldest swimmer in Team GB, is the sixth Scot to qualify, along with Robbie Renwick, Hannah Miley, Michael Jamieson, Caitlin McClatchey and Craig Benson, who qualified at the first set of trials.
Rebecca Adlington won the 200m freestyle in 1:58.68. In the same event, Stirling’s Lucy Ellis collected bronze with a personal best of 1:59.14.