This is the trickiest question I suppose. Though the common notion is Aloo aka Potato is a must to make the Fishball; actually, it is not. I have seen many families making Muitha without Aloo and have had that. If you ask me, the Muitha prepared without aloo, tastes way better. Potato acts as a binding agent and hence, people add it to the mixture of fish. This is the common and commercial process of making Muitha, though you can make muitha without aloo. I do add aloo while making muitha. It is easier after all. As such, it is a complicated recipe, needless to say, I prefer the easier process. Even then, Muitha without aloo in the filling is heavenly.