Maacher Kalia or Maacher Jhol means Fish (Maach) and (Jhol) in curry or gravy. The most commonly used fish to prepare Maacher Kalia or Maacher Jhol is Rohu (a kind of fresh water carp) or Rui Maach. If you do not have access to Rui Maach, you can also use Salmon, Pomfret, Sea Bass, Red Snapper, Tilapia or Catfish. Unlike in other parts of India, Bengali recipes call for the frying of the main ingredient in mustard oil, before it is added to the gravy or curry. This is thought to enhance flavors and cause the fish/ meat/ eggs, to absorb the spices in the gravy better. In some Bengali homes, this frying translates to deep-frying, while in others it means pan-frying. Take your pick, depending on preference.