I have personally only caught them in the Zambezi system (including Lake Kariba obviously) and Lake Chivero (where they were apparently put in accidentally).

Generally shallower areas (3 to 20 foot) prove to be the best for this species, and if there is some of that "red weed" (with what looks like mulberries on the top) it is usually a good area.  Around Fothergill is usually good for this species although they are caught all over Kariba.

If you look around these areas (Did you remember the Polaroid's ?), you will often see them moving around slowly along the edges of the weeds in the shallower water.
The bites when fishing on the bottom can vary from "Bait Robber" bites to a straight forward "yank". There are usually quite a few "robbers" around them, as they generally feed on snails in the weed, so do not get despondent when you only feel the "robber" type bites, some of them are BIG robbers.

The "Pro's" generally fish for them with spinners and the beginning of winter (around May, June) generally produces more and bigger fish.  The best colour and size seems to be a Copper Mepps 3 with Red dots on the blade.

SMALL TIP
If you are fishing with a spinner, cast a bit past them and retrieve "slowly" up to and just past them, and just drop it on to the bottom, and get ready to strike.
They also seem to move around in pairs, so if you get one the other will not be far away, so try the same area again.

SMALL TIP
If you are anchoring you can fish out to about 18 to 20 foot of water, and then cast you rig into the gaps in the weed, and then retrieve it VERY slowly. Use line between 10 and 15 pound test when fishing here, as the weeds are very strong, and you will either lose the fish or the terminal tackle.