can any one tell me how to make a rct bass?

Crush up your RKT to make them fine. This will keep them from getting lumpy. When you make your recipe, just start shaping the bass. I think you should print off some pictures or look at some books to get an idea of what the bass should look like. You can cover him in fondant and "draw" the scales on or try to find a tool or impression mat that looks like scales and press the scales into the fondant.

I just did one. I used a piece of copper tubing and covered it in rkt and packed them as tight as I could. I covered it in ganache and let it set. Them I covered it in thick fondant so I could shape the gills (and avoid lumps from rkt) I used the edge of different size round tips to make the scales. HTH.
Here's the fish:
http://cakecentral.com/gallery/1928771

You can also make scales using the curve of an icing tip.