Q: What is the significance of Santiago's struggle with the big fish?

Q: What is the significance of Santiago's struggle with the big fish?

Ans: 

Santiago succeeds in killing the Marlin after a long period of patience. With the sense of victory, the Old Man lashes the Martin alongside his skiff and sails back to his shore.
The first attacking shark is Make. 'It is a beautiful fish except its jaws. Here, the writer gives detail about the. kinds and appearance of sharks. The sharks tears of the Marlin’s flesh.
‘ But he drives the point of his weapon “with resolution and complete malignancy" into the shark’s brain. At this time, Santiago has to bear big loss as shark takes with it forty pounds of Martin, the harpoon and all the rope. 

The loss is increased when the Marlin’s blood attracts other sharks. Santiago sees the second shark coming and utters the single work “Ay". There is no translation of this work. He feels sorry for his big fish. But he is confident and resolute. “But a man is not made for dfefeat”, he said, "A man can be destroyed but not defeated”. He tries to cheer up his spirits. He thinks about many things including baseball. He enjoys his killing the shark. Santiago kills the sedond and third sharks, hateful, bad smelling sea-vengers as well as killers with his knife lashed to an oar. But when the
gallons take with them fully a quarts of the Marlin’s best meat. “I wish it were a dream and that I had never hooked it," says the Old Man, “I am sorry about it, fish. It makes everything wrong. Santiago kills the gallons but it breaks Santiago’ knife. .
By the time, the Old Man has clubbed the fifth and the sixth sharks put into death just at sun set. But a full half of the Marlin has been eaten away. “What will you do now if they come in the night?" Asks the voice inside the Santiago.
The sun sets. What could he do iri the darkness of night? “Fight them", he says. It seems that the Old Man has lost this fight  as there is nothing left of the great fish except the skeleton. But he succeeds to save his' honour and dignity. His honorable fight proves him the greatest fisherman. He proves that he can never be defeated. It is not the big fish who has beaten him. He will be  counted as the undefeated fisherman.