Paradeta is a sea food self service, in which you choose your fish or sea food on display; you can also choose between a vegetable salad or a fish soup to go with it, your drink and bread.
Salad is at 4€; a pity that they do not propose rice or potato to go with your fish or sea food. They give you a table number, and they call you to go and pick your dishes when they are ready
We paid 31€ for ~700g / 2 steaks of excellent fresh tuna, 2 salads, bread and two drinks.
This restaurant is near the Sants train & metro station. We went twice and will go back next time we go to Barcelona