Adam Peaty, James Guy and James Carlin all bagged gold as Great Britain's World Championship team claimed seven medals on the opening day of the Mare Nostrum leg in Canet.
Having broken the 100m Breaststroke world record with a 57.92 effort at the British Championships in London earlier this season, Peaty made light work of a world class field to take the touch in Canet in 59.83.
Japan's Pan Pacific champion Yasuhiro Koseki was the only other to beat the minute mark on 59.96 while Germany's Christian Vom Lehn - a former World Championship bronze medallist over 200m Breaststroke - was third and Olympic champion Cameron van der Burgh fourth.
Guy collected gold in his favourite 400m Freestyle, comfortably taking the touch by a second and a half in 3:46.84, having won the heats in 3:49.74.
South Africa's Devon Myles Brown was second in 3:48.28 while Canada's Commonwealth champion Ryan Cochrane touched third on 3:49.95.
Guy returned for a second medal in the 200m Freestyle, the British champion clocking 1:48.07 to narrowly miss out behind the Netherland's Sebastiaan Verschuren (1:48.05) but once again ahead of Brown (1:48.51).
Carlin's gold came in the 1500m Freestyle as she touched in 16:09.69 with fellow Brit Jessica Thielmann third fastest in 16:23.23.
The two other British medallists on day one were Bath Commonwealth champions Chris Walker-Hebborn and Siobhan-Marie O'Connor with Walker-Hebborn going 25.19 for silver in the 50m Backstroke and his girlfriend O'Connor turning out a 2:10.57 for silver in the 200m Individual Medley.