First of all, there's the circular nature of the environment; does he ever wish he could dart down a side alley, I wonder, or swim straight rather than in that eternal round? Can fish become insane?
Second, there's the little castle and shrubbery. We put it in there so that he wouldn't be bored, but he has to be sick of that view by now! When I tire of a room in my house, I paint it. What can Jack do? Swim away? No, poor thing. Just keep going in circles.
Third, there's the hope of freedom, which I suppose he gets every time I scoop him out to clean his world. He sits in the little waiting bin, perhaps wondering if this time he'll be dumped into the ocean, or a bigger tank, or something else, anything else, and then Bloosh! He's back in the bowl--same castle, same rock.
Poor Captain Jack. You see what reading Beckett has done to me?