Well, since this is a big part of my business I won't say about some of the things that I learned over the years doing this. I paid $$$$$$$$$ in dead fish, etc. etc. and for me to give all the info away? I just won't do it. You have to pay for knowledge, and payment could be paying a professor in a class room or paying for knowledge learned by paying for mistakes. BUT here are some lessons learned/cliff notes.
Do NOT run tanks that aren't full. It's called a slack tank. VERY dangerous if you have to make an abrupt driving direction change. I know of a fish hauler that had slack tanks in their truck, took an off ramp and they rolled the flatbed truck...... It wasn't pretty, both the people in the cab had multiple broken bones, and the truck was totaled.
Water weighs a LOT. You have to have the tanks tied down with straps strong enough, and you have to have lids on the tanks to contain the water. Splashing water out of the tanks is not a good idea if a state trooper or other police department just happens to see it. If you do not have electric brakes on the trailer, stopping distances can be greatly increased. If you don't distribute the weight in the trailer correctly and it starts to sway, and you don't have electric brakes on the trailer to stop the sway you will be toast. I will NOT use a trailer that has surge brakes. Period. Electric brakes or nothing AND you have to adjust the braking level according to the weight of the trailer. You can overload a truck/trailer suspension. Blow a tire, you better be able to control the vehicle while you stop it and you better have a good spare tire AND all the tools needed to pick up the vehicle/trailer to get the tire changed. I've heard of jacks sinking into hot asphalt because of a heavy trailer and the tire couldn't be changed. Is the trailer rated for that weight and are the tires rated for that trailer weight? Are you running the tires at the correct air pressure?
Hauling a tank that has more than 200 gallons in it? You better have a tanker rider on your drivers license. Haul more than 1,000# of O2? You better have a Haz-Mat placard on the truck and a Haz-Mat rider on your license.
Running ambient air is OK for a short run with low loading density, but for a long run or a higher loading density? You have to run pure O2. Running pure O2 without an oxygen meter is a recipe for disaster. Also, just like aerating a pond, using an air stone that does not make fine bubbles will cause problems. Even a Point Four O2 diffuser can allow you to kill fish if it turns upside down. You can kill fish by burning their gills by having the O2 levels too high. It WILL kill the fish. Running O2 means having redundant back up systems OR enough parts on board to fix whatever fails and fix it quickly. Don't run a defoamer in the tank? You can kill fish that way too by not letting the water off gas.
Keep fish in the same water for too long and you will kill the fish. You have ammonia build up and CO2 build up. You might see trout piping at the surface, think the O2 level is too low and pour more O2 to them if you don't have an O2 meter. It could be a build up of CO2 and you will smoke their gills.
The warmer the water, the less O2 it will hold. Fish are best hauled at 63°F water temp. You want the O2 levels to be between 9 and 15 mg/l. You might be able to get away with higher levels for a short amount of time, and possibly down to 5 mg/l for a short amount of time BUT that stresses the fish and causes them to use more O2. .
Fish density. It all depends on the species of fish and water temp, but when running pure O2 1/2# of fish per gallon of water is safe. At that density, holding fish for more than 16 hours is very iffy if you don't do at least a 50% water change. (Fish swim in their own toilet) You CAN haul fish at a higher density, but that is like playing with a lit firecracker that you don't know how fast the fuse will burn. Catfish can be hauled at a MUCH higher density. but if the fish weren't purged for 3 days prior to hauling, the haul density has to be lowered.
Water temp/pH change. No more than 5°F per half hour temp change, and no more than 1.0 pH per hour change. I have killed Walleye fingerlings with a 1.3°F temp change.
When using O2, you HAVE TO HAVE a DOT approved safety cap on the tank when driving down the road. It's a recipe for a ticket if you don't have a safety cap on it. Even with the regulator on the tank, it's gotta have a safety cap on the tank..
Try to cool down the water with ice? You better have a chlorine or chloramine neutralizer on board to use. Ditto for using city water.
Some states you need a fish hauling license to transport fish. If you don't have a receipt and you have fish in greater number than the bag limit, OR fish smaller or larger than you can catch and keep, you can get spanked for that too. Take fish from one state to another without having the proper permits or health certs? Google what a Federal Lacey Act violation costs. Oh, and that is a felony too.......
10# of small fish need more O2 than 10# of large fish.
Galvanized tanks? Not this boy. Take a look at what the haul tanks are made of. Absolutely 0 are made from galvanized metal. Zinc is toxic to fish. Add salt to the water to stimulate the slime coat just causes zinc toxicity faster. Again, you may "get away" with it for a while, but sooner or later you will get burned.
Putting big fish in the tank with small fish is a recipe for killing the small fish. They get beat up by the big fish.
Hauling in hot weather or cold weather and not using insulated haul tanks? Good luck. I have hauled fish for 12 hours in 10°F ambient temperatures. Even with insulated haul tanks the water temp dropped 13°, and try to adjust an O2 flow control meter when it's covered with 1/2" of ice.......
Just because you are running pure O2 and have an O2 meter doesn't mean that the O2 levels 5 minutes after the fish are in the haul tank will be the same 20 minutes down the road.
Use O2? You will need a diffuser stone made for O2, a regulator and a flow control meter. Since you need redundancy, now go price at least one extra of everything.
That's why it costs $$ to haul fish. Equipment costs, Knowledge expenses and driving down the road expenses. $4.30/gallon of diesel? That's $0.43/mile @ 10 MPG JUST FOR FUEL. For a hobbyist for one trip, you might be able to get away cheaply. Buy $500 worth of fish, get home, see that they died on the trip, now they just cost 2x as much to replace IF you can find those same fish.