Interesting. It isn't allowed up here, at least in the regular mail. I can only imagine what would happen if you had a leak in a bag of mail. One guy told me that was why he liked breather bags; you couldn't tell there was water in the box by shaking it.
I recently shipped some fish to Oregon from Michigan, the Post Office stamps the package Liquid if there is liquid inside (also Fragile and Perishable). There are also rules for packaging, for example, enough material to absorb all the liquid if it should leak, and an additional water resistant layer outside the initial container (styrofoam box works well).
This doesn't ever go by regular mail, anyway. I ship Express or Priority, depending on various factors. I don't believe liquids are allowed in the regular mail here, either.
Nice of you to post the link to the USPS regulations for shipping live cold blooded animals.
I know it by heart. I have been mailing fish for 45 years.
All my Plecos are about one year old at time of sale. I never sell fry.
Currently all I have are Leopard Frog Plecos, Peckoltia compta, (L134) They are about 2-1/2" and max out around 3-5/8". 6/$240 + box +postage.
Hypancistrus sp L333, sometimes called the Yellow Queen Tiger.
They are also about 2-1/2" and reach about 4-1/2". 6/$150 +box + postage.
These are both warmth loving, peaceful and very colorful plecos. They are mainly carnivorous. I raise them on earth worm sticks and frozen blood worms. They do not eat algae. One of these can replace 4 or 5 Corydoras as your bottom feeding catfish.
Both are very popular among Discus keepers but both make good tank mates for peaceful, warm community tanks. They will not harm the smallest Tetra yet make good tank mates with Dwarf Pike Cichlids
Brazil's Ibama(Brazil's Interior Dept)
banned fishing and trade in all of their Hypancistrus pleco species.
Only tank bred or illegally removed specimens from Brazilian waters are available.
Hypancistrus species from the Orinoco tributaries remain legal in the tropical fish trade.
The best known example is the famous Hypancistrus zebra that sells for about $180 each.
I breed all my plecos and sell them to people all over the lower 48 states.
I use breathable bags and a mild fish tranquilizer. In tests I have run the fish were still doing well after being bagged for seven days but I had to let them out so they could resume eating.
I buy insulated shipping kits which includes a dense 1-1/2" thick walled styrofoam box inside a matching cardboard box well marked, "PERISHABLE"
I modify my breathable bags by using an impulse sealer to seal the 90* corners at about a 45* angle. Pleco spines easily puncture a bag if there is any place they can get some leverage.
Cichlids require similar precautions due to their sharp spines.
I always use a barrier bag as my box liner and I wrap each bag/fish with a paper towel to maintain maximum gas exchange and help meet the absorbent material requirement. I have shipped out about 150 Plecos so far this year with a 100% survival rate.