With great radioactivity...

[The_root_of_all_evil]

...Comes great animal powers, or at least according to Marvel. So, takinhg their idea of how physics work, what radioactive animal would you get bit by.
And what powers would you borrow from your bitee?

 

[Kaboose the Moose]

Animal: llama

Power: super spit

 

[Biosophilogical]

Animal: Dove

Power: Giant super, white, feathery wings, hollow bones, strong bone density and anything else necessary to generate sustained flight without technological assistance.

Alternatively;
Animal: Whale

Power: The ability to hold my breath for large stretches of time combined with the ability to swim to great depths without being crushed by the pressure.