Some cells have many short, hairlike structures on their surfaces. these structures are used mainly for what

Movment and absorbtion of nutrients. I think the structures that you are refering to are the microvili.

answer: 20 percent

the fish culture has become a developing commercial practice in developing countries which is already prominent in developed countries of the world. the major fish protein demand is being supplemented in developing countries is   fishing to meet the needs of the growing population. therefore, in some developing nations, the percentage of animal protein from fish in the diet can be as high as 20 percent.