The nutritive value of diet is greatly enhanced by inclusion of fish in diet. Which of the following nutrient is deficient in fish?

Fish is nutritious food rich in proteins (15-25%). The fat of fish is rich in unsaturated fatty acids and A and D vitamins. Fish bones are rich in calcium, phosphorus and fluorides. Fish are less rich in iron (0.7-3 mg/100 g) than meat. Freshwater fish do not contain iodine, but sea fish do. There is practically no carbohydrate in fish. Ref: Park's Textbook of Preventive and Social medicine, 19th edition, Page 500.