A leukocyte is responsible for:

bringing oxygen to the other body cells
fighting disease by phagocytosis or antibody production
causing muscle contraction
conducting nervous impulses throughout the body

The second one is correct

Explanation:

A leukocyte is responsible for the immune system

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.