When you transfer new fish to your aquarium the first thing to take care of is the adaption. Each aquarium has different temperature and water quality than the plastic bag where you are carrying your fish. What adaption is about is your fish to adapt gradually to the new conditions.
How to do the adaption? Since your fish are inside a plastic bag, open the bag and fold the edges so that to create a “life-buoy”. Dip the bag in the aquarium and add 1-2 glasses of the aquarium’s water in order to mix the water of the bag with the water of the aquarium and then let it flow on the surface. To avoid the bag turning upside down you can stabilize it with a clothes clip on the aquarium side. Repeat this procedure every 10 minutes for at least 30 minutes before you release the fish in your aquarium. Prefer to move the fish to the aquarium without emptying the water, using a net. The adaption can be performed by using a bucket as well.
The above procedure has to be carried out for all fish, irrelevant of how “resistant” your fish are. A good or bad adaption is critical for their survival in your aquarium.