Police said the indecent assault happened around 00:40 this morning (Friday 20 December) in Tanguy’s.
Describing the alleged sequence of events in an appeal for more information, they said: “A man in his 20s was allegedly indecently assaulted whilst on the dancefloor at the rear of Tanguys.
“A 23-year-old man was arrested a short time later and remains in police custody this morning, whilst enquiries continue.”
Anyone who was at the nightclub last night or has more information is urged to ring Police on 612612 or make an anonymous report via the Crimestoppers website.