Norman lampeye fish

Hello!

so I have had my tank for a month now and my betta has been in the tank for just over a week. I went to the aquatic shop today and bought 5 schooling lampeye norman fish however after introducing them to the tank one of the 5 isn’t joining the school and is just swimming in the tank alone.
I just wondered if anyone knew the reason for this? just wanted to make sure everyone was okay?
In the picture he is in the top left

tha

If you just introduced him today, most likely it's just adjusting. Give it some time, and keep an eye out for any signs of it being sick.

This is probably going to lead to trouble. Male bettas are not community fish, and should be housed alone. Adding small fish that also occupy the surface region in the tank is almost certain to lead to trouble. You should separate these ASAP. The one might be under serious stress due to this already. Fish show aggression not only by physical interactions, but also by releasing chemical signals called pheromones and allomes which other fish read.