What is the meaning of this sentence which is said by Santiago: "The setting of the sun is a difficult time for all fish."
As a novel, The Old Man and the Sea is preoccupied with questions of age, mortality, strength, and change. Santiago, the fisherman, is an elderly man whose physical health and luck are deteriorating, so much so that he is considered "salao," or unlucky. He must battle against these forces in order to survive, and, perhaps more importantly, to regain his pride and reputation.
Thus, when Santiago says that "The setting of the sun is a difficult time for all fish," he may well be referring to his own predicament. He is an aging man - that is, he is in the sunset of his life - and it is becoming progressively more difficult for him manage his strenuous occupation. If he does not fish, he will sink deeply into poverty. He may be too old and too sick to pursue other employment. Further, Santiago's life is "setting" in that the joys and adventures of his youth, symbolized by lions on an African beach, are far away, and his future is uncertain. What will happen to him in the coming years? Who will care for him when he is too frail to work?
This quote can also be understood in terms of the broader context of literary modernism, which refers, loosely, to a school of writing which spurns embellished or flowery prose for simple, cutting statements and depictions of an ambiguous world. Indeed, Santiago's statement is short and straightforward; there are no unnecessarily large or complex words, and its symbolism (the setting sun) is quite ordinary. Nevertheless, it conveys profound tension and emotion about aging, the future, and mortality. Indeed, it is an excellent example of the paucity and potency of prose for which Hemingway is famous.