I admit I am not an expert on different fish species, however, there seems to be a valid reason for confiscating it. Snakehead fish don't appear to be native but Asian fish and are referred to as "Fishzilla."
While the owner may have been a responsible pet fish owner, who can say DEFINITELY what may have ultimately become of it. Circumstances may, at some point, require that another person be charged with the care of it and that person decides to dump it into the first lake or river they come to. I realize this is hypothetical but still such things have happened thousands of times. That's how those giant Boa snakes have ended up in the Everglades and are reproducing at a rapid rate.
Personally I don't think it's as much about government interference in our lives as it is about protecting our natural ecosystem. Perhaps the decision was based on something like the law that says it's illegal to dump certain fish from one river or lake into another. jmo
I found this information to be thought provoking:
http://www.dnr.state.md.us/fisheries...snakehead.html