Ceviche works to no set rules, varying wildly in look and taste from Central to South America. I experienced one in Nicaragua that contained peas and pineapple. It was odd but good. Other firm, white fish, such as bass or bream, will do fine here, but I think the plaice works particularly well and it is very reasonably priced. It is imperative that the plaice be very fresh, as any trace of fishiness will spoil the end result.