[Tijeras_Slim]

Water is used more because of its ability to shield against neutrons, which unlike alphas is much more penetrative and has a high Q value.

[GonzoGOP]

Your right, I was thinking beta particles/neutrons. Heck if all its throwing off is helium nuclei that's an even better reason to just let the darn thing alone. You won't even get mutations in the fish unless they eat stuff.