thanks all - the setup is an old 5-gallon aquarium that I put on its side. I moved one side panel to the new side and took that black plastic frame off the aquarium and made a lid and side vent out of it. And glued in a land/water divider.
It's small, but then, there's only one of him and he's little. He loves the big leaves of that plant (not sure what's that called).

Then again, it was his fondness for big leaves that got him in trouble in the first place...as he was hiding in the kale

On his size/age question...he got to Alaska in early Sept at 3/4 inches long - so he wouldn't have metamorphosed just a month before, or would he?