If you have a sim with no mechanical skill points and want them to start catching fish quickly, have them go to a comm lot with a pond and wait for several sims to arrive. Then have the sim start fishing and immediately start asking other sims to join. From my testing, they will start catching fish fairly quickly if there are a bunch of other sims also fishing with them. Even if they don't have many mechanical points.
I tested this with sims that had no points and sims that had up to two mechanical skill points. When other sims weren't invited, they quickly got too frustrated and gave up. But with other sims joining them, they got a boost to their social and the frustration was brief. But most importantly, they started catching fish. I did this to see if I could get my sims to fish for their food, no stocked refrigerator, only a grill. Now I know how to feed my new families super cheap.