The fish most often given to prepare ca cha bong is snakehead fish (ca loc), followed by ca hoi (salmon) and ca thu (codfish). I used codfish because it was cheaper and because I suspect that, given the sheer amounts of nuoc mam that goes into the recipe, the actual taste of the fish is of little consequence. You might, though, need to adjust the amounts of nuoc mam and sugar if you use other fish (for instance salmon, which is fairly sweet, possibly requires less sugar). I've also seen ca ro phi (tilapia) used to make ca cha bong.