Describe the relationship between the old man and the fish in The Old Man and the Sea.
I think that you could probably go two different directions with this answer. A common answer is to describe the relationship between Santiago and the marlin as a respectful relationship between two equally strong opponents. The man and the fish are not necessarily enemies of each other, but the fish is definitely in a battle for its life, and it generally wins those fights as evidenced by the additional hooks found on it. Santiago is a fisherman, and he has great respect for the sea and the animals found within it. When the battle is over, Santiago is both relieved and saddened, and readers see just how respectful Santiago is when he can't protect his catch from the greedy sharks.
The other way to describe the relationship is to go toward the direction of saying that the fish is nothing more than something he needs to obtain to continue his existence. This is a cold relationship and quite an existential relationship. Santiago is a fisherman; therefore, his existence is defined by his relationship with and dependence on the sea. Catching fish allows him to live and gives him happiness. The fish then becomes a means to an end. He has gone for months without a catch, and bringing home this super fish will likely grant him renewed feelings of youth and vigor as well as money to feed himself with.
The relationship between the old man and the fish is one of respect and dignity. The old man reveres the fish constantly talking to him and asking what he's got next for him. He is awed by his size and by the fact that he keeps going and trying to escape. That's why he's so upset once the battle is finally over. He knows he's beaten this fish and he would like to bring him in with dignity and respect. When the sharks start to get after him, he knows that he's done a disservice to the fish by not being able to get him in and save his body from the sharks. You can also support this idea by talking about the point when the fish launches and the old man mentions that their eyes meet. The fish is impressed with the old man's ability to hang on, something others have not been able to do, as evidenced by the number of hooks hanging from the side of his mouth when the battle is finally over.
If you need detailed quotes, there is a link below to detailed passages.
When the old man, Santiago, first encounters the fish, he is weary and cynical, having been unlucky in his fishing for so long that his apprentice's parents have forbidden the latter to sail with him. When he first hooks the enormous marlin, his feelings are that of excitement that his luck has finally turned. It is this excitement that keeps him pushing through for the next two days of struggle with the great fish.
While Santiago is fighting to bring the fish in, he begins to think of it with the utmost respect, admiring its tenacity and endurance. He even begins to think of the fish as kindred and as too mighty to ever be eaten by any man. It is perhaps this feeling more so than Santiago's dashed dreams of fortune that makes the ending of the story most tragic for him.