Fish pickle is a preserved food item made through anaerobic fermentation in brine or immersion in vinegar. It's often spicy and pungent, using ingredients like lime, gooseberry, ginger, and garlic. While traditionally made with vegetables, fish pickle has become increasingly popular. Common fish used include prawn, tuna, pomfret, and mackerel. The process involves preparing the fish, mixing it with spices, and preserving it, resulting in a flavorful and long-lasting condiment.