Spearing a fish (not with a speargun and swimming) pretty much requires being able to pin the fish to the bottom. If you don't pin the fish it'll just be knocked and swim off. I've tried a couple of times and was successful once. LOTS of patience and slow moving required, I'd rather throw out a couple of lines and go do something else. At night with a good flashlight is much easier, frogs are out and some fish kind of sleep. I've walked across low water dams at night and you can shine a light and see the "sleeping" fish.

You mentioned it, but I think it needs repeating. The Cold Steel Bushman is a fairly decent knife with a socket made to put a handle on it. It doesn't have to be a handle for a spear either, a 1 or 2 foot handle makes it a machete and gives you a pretty good swing for chopping. You can also keep your mini-PSK in the handle. Include a couple of woodscrews and you can use your SAK or pocket tool to attach the handle to the knife. The knife has a lanyard hole in it that works fine for that. The downside is a crappy sheath.