bro tis is helpful.
what do you meant by airtight flask? those flask we have are pretty small. you meant packed the fish into plastic bag and put it into thermo flask den check in inside luggage?
if we chek in luggage, it definitely be very cold in the luggage compartment. will putting in styrofoam box work? saw LFS shipment and they usually packed the fishes into styyrofoam box.