I am told that in it's original form it was a cheap and easy meal for fishermen. They were able to use up the fish or fish parts that weren't saleable. The fish, along with tomatoes, local peppers, garlic and saffron is used to produce a stock in which rice is cooked. It is the rice that is the essential part of the meal but, if you have any decent fish available, that can be cooked in the stock too. Normally the fish is served separately. So it really is rice with fish rather than a rice and fish mixture.
The whole lot is served accompanied by ali-oli - an emulsion of garlic in olive oil - which lots of we foreigners mistakenly believe to be a garlic mayonnaise.
Now Spaniards eat a lot of fish. Even the smallest of supermarkets often have extensive fish counters. In landlocked parts of Spain fresh, not frozen, fish and seafood is readily available. Maggie and I aren't big fish eaters. I like seafood well enough but fish bones give me the willies and Maggie's just not taken with the fishy taste. Nonetheless we decided that living on the Mediterranean coast and being surrounded by fish resataurants we should give this local delicacy a go. We chose a restaurant that we've heard good reports about. It shares a fence with the fish quay. Being a Bank Holiday the place was heaving when we got there about 3pm. We had salad, mussels, prawns, cod fishcakes and croquettes followed by the caldero.
The caldero was alright I suppose but it was a bit like one of those student meals knocked up with anything left in the cupboards rather than a dish honed to perfection over the years. I much prefer the the paellas and fideuás of Valencia and if we're only talking about traditional Cartagenero food then give me the local bean stew called michirones anytime in preference.