Here is what I copied from that website. This tells EVERYTHING you need to know about shipping fish.
They say the world is smaller than it ever was before. When it comes to buying and shipping fish this is true. I live here in Texas and can get fish from all over the world, but especially all over the nation. A breeder in New York can send me some great fish the same day I get great fish from Florida, California, and other places. The great news is that you can use this same idea to share great fish you have bred with friends and family, you can use shipping to get your fish in a cross country move, and you can even sell fish to others all over the nation. The only thing you need is a great plan for shipping.
The first place to start with any shipping project is the box. You want a box that is big enough to put all your fish in after they have been bagged. You will also need room for insulating the box to protect the live fish from temperature changes and extremes in hot and gold. At the same time you don't want your box to be too big. A box that is too big will make it hard to make sure that your fish don't do a lot of moving around and could cause damage to the fish.
In addition to finding or buying the perfect size box you will also want to make sure that you are buying a very sturdy box. Most of the time the carrier you choose to use isn't likely to know or care that you have live fish in there. Your box will be stacked up, pushed around, and pressure will be put on it. Make sure that your box can handle all of this hard handling.
Insulate the box.
Once you have your box you will want to make sure that you insulate it. This means that you should place a Styrofoam cooler or similar set up inside the box. You can always use a cooler if you have one or want to buy one. There are also some other Styrofoam boxes available. However, if you are looking to save money you will want to make your own. You can buy a large sheet of Styrofoam insulation from your local hardware store. Cut this into the perfect size to fit into the box on each side (including a lid). It can be a good idea to tape up your edges because if there is a water leak the Styrofoam will protect the cardboard box.
Bag Your Fish.
Now that you have a great box that will protect your fish from shipping hazards and hot and cold temperatures you will want to bag your fish. There are two options for bags. You can choose a thick plastic bag that is at least 1.5 millimeters thick (or thicker). These bags come in a wide range of styles, seams, shapes, sizes, and so on. Your best option is to try a few different bags and figure out the ones that you like best since it is usually a preference.
The other option is to choose a Kordon breather bag. These bags are made of a special material where they are supposed to let the carbon dioxide out of the bag and let oxygen in. There are a few good points about these bags and a few disadvantages to them as well. First you are making sure that your fish has plenty of oxygen and you don't have to worry about a large bag because you don't need 2/3 of a bag of air. It also makes it possible to ship in a smaller box. For most fish these bags work great though there is a lot of debate as to whether fish shipped in them do better than fish shipped out of them. At the same time some fish shouldn't be shipped in them including those that breathe from the surface of the water (bettas, gouramis) and those that use surface air to move up and down the tank (corydora catfish). It is best to make sure that the fish you are shipping can be shipped safely in these bags. These bags also cost a lot more than other types of bags. These bags are currently only available in a large size and a small size, which can be hard for medium size fish and shipments.
Now its time to bag that fish!
Fill the bag. If you are using a plastic bag fill it enough to cover the size fish that you are shipping no matter how the bag moves (guestimate), but no more than 1/3 of the way full. If using a Kordon Breather bag fill it most of the way up.
Add an additives. While you don't have to add additives and most healthy fish will do fine without adding anything there are many products that people use to make it easier for their fish to make it including (but not limited to) Bag Buddies or Stress Coat.
Next net your fish and place him in the bag. This tends to be a traumatic experience, but try to be as gentile as possible.
Tie up the bag. For a regular bag you will need to fill it with air with an air pump (not your breath because this will be mostly CO2
and not oxygen) or by catching the bag. Catching the bag takes a little practice, but it really does work. You will need to quickly grab the bag to seal in the air. For Kordon breather bags, you don't need to worry about air and you can just tie it off. You can choose to tie a knot (can be best) or use a rubber band to secure the top.
For regular bags you should check to make sure that your fish will have enough water no matter how he is laid. Try laying him on the side and even at an angle to be sure. If he doesn't have enough water then you will need to bag him again.
Next you will want to double bag your bag. This makes it so that if there is a leak it will leak into the second bag rather than into the box. To do this you should gently flip the bag upside down and slide it into a second bag. Tie this one as well.
Place them in the bag and cushion them. The best option for cushioning is to fill the box with pieces of Styrofoam (from cutting up the board) or to add Styrofoam packing peanuts. This will give it good cushion and that impact won't change should their be a small leak (like newspaper or shredded paper).
If you need to you should tape a heat pack to the bottom of the lid. Make sure it is very secure so that it won't fall down on the fish. You should add a couple of layers of paper between the heat pack and the bags and Styrofoam inside.
Attach your lid and seal up your box. Use plenty of tape to make sure it is all secure and that your box has that added security.
Finish by labeling it. You shouldn't label it "live fish" because it is sometimes refused by airlines that carry mail. However, you should label it "fragile" and possible "fragile" so that it arrives as safe as possible.
Ship Those Babies Out!
Once you have your fish all ready to go you should ship them out as soon as possible. Don't leave them laying around the house waiting, because the sooner you get them out the sooner they can be processed and on their way.
Shipping can be done by Priority mail if the weather permits it. If it is really hot or really cold you should avoid shipping fish Priority. Express costs more, but will get your fish there faster because priority can take more than 3 days! You can also ship fish via UPS and FedEx for fast options, but often times these are expensive options.
Make sure you send it with a confirmation and that you let the people who will receive your fish know that it is coming. This will make it possible for them to be there when the package arrives.
Sit Back and Relax.
You have done a good job and now all you can do is sit back and relax. Your job is done and in most cases that will be plenty to insure that you have fish that arrive healthy. The only time that isn't true is when the fish aren't very healthy to begin with so make sure you are selling healthy fish and you have it in the bag!
Shipping fish does take a little work. However, it can be rewarding, both in knowing that you are sending your fish out there and even financially if you are selling and making money with your fish. There are many different choices and you are going to have to figure out what works best for you and go from there!