On another forum, on the subject of shipping larger spiny fish, I found this for "spiny and toothy fish" from a very experienced shipper:
There are thicker PE bags. There are 15 mil or some such clear PVC bags.
One can fashion a sack or a box out of 45 mil rubber and place this in a secondary plastic sack.
Also, one can place a hard(er) plastic jug akin to a milk jug or a hard(er) plastic box inside a plastic sack . . .
So just let me know if you want to make this happen! ? ? ?
And just so you know . . . I'm half kidding, but half serious.