Do julii fish swim in shoals?

Yes, Julii fish do swim in shoals. They like to swim in a group of 5 or 6 ,I found this answer from a professional.

I brought a Julii fish when my tank was set up and the water was at the correct temperature for tropical fish (25 degress c), then exactly a week later, I brought another Julii fish and put it in the tank, straight away they went to each other and swam togethor. I think they might be mating already even though they have been togethor for a few minutes, BUT if your tank is full i personally would recommend not to get two of different genders just incase they mate.