My daughter SnowyAngel took about 9 fish through as carry on hand luggage, and yes they DID go through the xrays. That was some of their Bettas plus fancy male guppies. The rest all went in plastic bags(lots of air, little water) inside a big foam carton, well duct taped, donated from the local LFS, as cargo

and THEY all survived too.
This is via two different flights, through airport luggage handling between planes yet and a distance of over 2000 miles. SO yeah it can be done. Mind you, security tipped the carry on bag over for some strange only known to them reason

...it was quite tiny didn't need to be tipped....so my daughter and her boyfriend had to rush to the washroom right after and put new water into the little plastic cups with airholes that everyone was in(they had Aquasafe or somesuch with them, for chlorine obviously). Snowy may come on here and mention it. Their fish did great.
They DID phone the airline ahead of time. They said no problem, though the airport where they checked in at, had never flown fish before and were like "What?!?!?"

But they took the fish. Snowy used a zippered beer/lunch
carry bag from Wallyworld...worked great!
SnowyZMom B)
(no disrespect to Walmart there, my hubby works there)