When I was reading the book, I really did not notice any symbols. Luckly, after writing about the book for a couple days I noticed that the fish could very well be a symbol for the conflict and struggle the old man goes through.
First, the fish lurches, and the line cuts the old man's hand (Hemingway 30). This makes the old man's job harder and more painful than it already was. I think that the fish is being used to escalate the conflict and make it more challenging for the old man.
While the old man has been trying to uncramp his left hand for quite a while, the fish jumps out of the water (Hemingway 33). This is the first time the old man's body is starting to show some weariness, and also the first time the old man sees the fish. I think the fish is being used as a symbol for the challenge the old man is having because the first time it is seen is while the old man is really struggling to get his hand working again.
When the fish finally decides to start jumping, the line is pulled from the old man's hands so fast that both of them are cut open (Hemingway 41). Now the left had is cut as well as the right, and the right has been hurt twice. I think that here again the fish is making the conflict more intense.
Epecially when the fish is circling it is apparent that it is a symbol. After every time the fish goes around the old man has to fight harder and harder to keep himself from failing (Hemingway 46). He starts out doing quite well, but after many passes it becomes a true struggle to keep working on the fish. Because of this, I think the fish is being used as a symbol here.
At the end, the fish is merely a pile of bones, left on the beach as trash (Hemingway 59). I think that this symbolizes the old man letting go of his struggle and moving on.
Hemingway, Ernest. The Old Man and the Sea. New York: Scribner, 2003. Print.