When you are recieving shipped fish you can take action to make sure they have an easy transition. Open you box in a dim lit room. These fish have been in darkness for at least 24 hours and they need to be adjusted to the light gradually. When you have your fish out of the box they need to be slowly acclimated to your own water before they are released. It may be a good idea to ask your shipper what their water looks like so you have an idea what your fish are going to have to adjust to. You'll want to either float your bags in the tank or empty the fish with water into a cup for acclimation. Add small amounts of your tank water to the bag or cup over a period of about an hour. Net the fish and add it to your tank and discard the water in the bag. It's best to keep the tank lights off while the new arrival settles in. If the fish is going into a community tank, quarantine would be best. Wait a few hours for them to settle in before offering food and you should be fine