By: Rabbi Ari Enkin
There is a well-known custom to eat fish on Shabbat. Indeed, the Shabbat meal frequently begins with a first course consisting of fish. This is no doubt partly due to the story of “Yosef Mokir Shabbat”.
The Talmud tells the story of a certain impoverished Yosef who always honored the Shabbat with the best possible foods. In Yosef’s neighborhood there lived a wealthy Gentile. Local fortunetellers warned this wealthy Gentile that Yosef would one day acquire all of his wealth. Not wanting to see all his hard earned possessions end up in the ownership of someone else, he went and sold everything – purchasing a precious stone with all the proceeds. He kept this precious stone set in his hat so that it should be with him wherever he went. Once, as he was crossing a bridge, a wind came and blew off his hat and jewel sending it into the river below, and the man watched as his jewel was swallowed by a fish that then disappeared.
One late Friday afternoon Yosef was walking in the marketplace. A fish merchant desperately trying to sell his best catch before the onset of Shabbat approached Yosef surveying his interest in buying the fish. True to his reputation, Yosef did indeed purchase the large and tasty looking fish in honor of Shabbat. Upon arriving home and slicing open his fish in preparation for cooking, Yosef found a diamond – the rich man’s diamond – in the belly of the fish. The sages teach us that it was in the merit of Yosef’s extensive honoring of the Shabbat that he merited to receive this diamond which we are told was worth thirteen roomfuls of gold.
Fish is especially appropriate for the Friday night meal, although it is ideal to partake of fish at all three Shabbat meals. If one only has enough fish for one meal, it seems preferable that it should be saved for the Shabbat daytime meal.Some authorities argue that the third Shabbat meal is actually the ideal time to eat fish. The popularity of fish on Shabbat may be due to the fact that fish (“dag”) is the gematria of “7”, suggesting that we are to eat fish on the seventh day.As with anything one eats on Shabbat – one’s personal gastronomic preferences and conveniences take priority.
There are a number of additional explanations for the custom of eating fish on Shabbat. One explanation has it that eating fish represents a three-part continuity in the order of creation: Fish were created on Thursday, Man on Friday, and Shabbat on Saturday. Others suggest that eating fish on Shabbat represents the feast which will take place in Olam Haba, the next world, in which the Leviathan fish will be served.
 Shabbat 118b  Magen Avraham 242:1  O.C. 271:3  Minhag Yisrael Torah, O.C. 291:1,Ta’amei Haminhagim 305  Mishna Berura 242:1  Ta’amei Haminhagim 305  Bava Batra 75a, Rashi;Bereishit 1:21. The Leviathan is a giant fish which was created on the fifth day of creation. God created one male Leviathan and one female. The male, we are told, was castrated, and the female was set aside for that special banquet discussed above. See: Tehillim 74:13-14, Iyov 41, and Yeshayahu 27:1 for biblical references to the Leviathan.