Each replication fork requires both leading and lagging strand synthesis. why?

Because each strand acts as a template for the synthesis of a new, complementary strand.

Explanation:

This is known as semiconservative DNA replication. Leading and lagging strands are complementary, antiparallel strands (one is 3'-5' while other is 5'-3- direction) which are replicated differently. The leading strand is replicated  continuously while the lagging strand is replicated in fragments-Okazaki fragments. Replication of both strands is performed by DNA polymerase.

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.