The gold fish are the best to catch; they give you more points. The red fish give you more speed, but you can also get that by holding down your mouse button, so it's not that big a deal.
I hold the mouse button down most of the time, except when I get too close to the ice holes so I don't fall in.
You have to get the hang of the way Waddell moves. He doesn't just follow your mouse movement; he has a circular way of moving that mimics ice skating.
I haven't noticed any sort of penalty for bumping into the seals, so don't worry about that.
On at least one level (I forget which one), there's a big snowy patch in the middle. Waddell can walk across it for a shortcut, but he's a much slower walker than he is a skater.
Other than that, just try to catch enough fish to meet the goal before time runs out so you can move to the next level. Good luck!
(Anyone please feel free to correct me if I got any of this information wrong. These are just my observations from playing for the past few days, and I haven't been making a close study of the point system or anything like that.)
---------- Amneris added 48 Minutes and 30 Seconds later ----------
Okay, I was just playing and trying to pay closer attention to what happens when you bump into the seals. At first I was thinking it was making my goal meter go down a little, but then I realized that that happens when Waddell just stands there and doesn't catch any fish for a while, too. So I'm back to my original thought, that it's okay to bump into the seals.