The correct answer is option 'D', which states that the percentage of protein in fish is less than 30. Fish is generally considered a good source of protein, but the exact percentage may vary depending on the type of fish and its preparation method. Here is an explanation of why the answer is 'D':

Fish as a Protein Source:
Fish is an excellent source of high-quality protein, which is essential for various bodily functions. Protein is made up of amino acids, which are the building blocks of our body. It plays a crucial role in muscle growth and repair, enzyme production, hormone synthesis, and immune function.

Variation in Protein Content:
The protein content in fish can vary depending on several factors, such as the species of fish, its age, habitat, and diet. Some fish species are naturally higher in protein content, while others may have lower levels. Additionally, the protein content can be influenced by factors like the fish's fat content and the way it is cooked.

Factors Affecting Protein Content in Fish:
1. Species of Fish: Different species of fish have varying protein contents. For example, lean fish like cod, haddock, and sole are known to have higher protein content compared to fatty fish like salmon or mackerel.

2. Age and Size: The age and size of the fish can also affect its protein content. Generally, younger fish tend to have higher protein levels compared to older ones.

3. Habitat and Diet: Fish that live in nutrient-rich environments and have a diverse diet may have higher protein content. For example, fish from the ocean or freshwater sources with abundant food supply may contain more protein.

4. Cooking Method: The way fish is prepared can also impact its protein content. Grilling, baking, or steaming fish without added fats or oils is a healthier cooking method that preserves the protein content. Deep-frying or breading fish can add additional fats and calories, which may reduce the percentage of protein.

Conclusion:
In conclusion, while fish is generally considered a good source of protein, the exact percentage can vary depending on various factors. However, based on the given options, the correct answer is option 'D', which states that the percentage of protein in fish is less than 30. It's important to note that the protein content in fish remains relatively high compared to other food sources, making it a valuable addition to a balanced diet.