During the war, a large number of farmland was abandoned and a large number of people were displaced. The taxes of ordinary people are very heavy. Not only will people be dragged to the battlefield, but most of the food collected will be handed over to the government. Therefore, there is no extra food for the people, and it will be easy to eat. If there is a shortage of food because of the war and the people's living places are not fixed, it will be difficult to ensure that there are rivers and lakes where people gather, so that people can catch fish and shrimp.
What's more, in ancient China, fishermen belonged to a special group of farmers, and ordinary people didn't have special fishing tools, so they couldn't catch fish and shrimp in batches to supplement the energy needed by protein to supplement the human body.
The second point is the famine period. In ancient China, the famine that caused a lot of food shortage was nothing more than drought or flood. If there is a drought, the water level of mountains, rivers and lakes will naturally drop, and the fish and shrimp inside will be sunburned. Naturally, there are not enough fish and shrimp to provide people with protein and energy. If there is a big flood, ordinary people will have no place to stand and live. How can they go fishing and shrimping? Therefore, in ancient China, no matter the war or natural disasters, ordinary people could not concentrate on catching a large number of fish and shrimp at the first time. Moreover, to take a step back, in the biological chain, fish and shrimp need to eat food to maintain their lives, and fish and shrimp themselves consume some energy. When plants are not enough for human beings to collect and eat, there will be fewer fish and shrimp that need to consume energy from plants like human beings, and it will be more difficult to ensure human energy or protein supply.