My thoroughly unkosher mother-in-law hosted Thanksgiving this year and was gracious enough to cook a kosher turkey on my and her grandchildren's behalf. While raised in a strictly kosher home, she forcefully seized her dietary destiny at 18, when along with two girlfriends, she hopped on the A train in Manhattan's Washington Heights and headed down to a fancy Midtown restaurant. With great fanfare she proceeded to order the special - shrimp in lobster sauce - a fabulous double whammy of an unkosher delicacy. Though digested in the latter years of the Eisenhower administration, the experience of momentously breaking with ancient Jewish dietary tradition proved so thrilling that to this day my mother-in-law relishes the episode as if the busboy had cleared away the dishes only moments ago. Why the thrill? By violating the sacred kosher laws that evening long ago, my mother-in-law was breaking with strict tradition diligently followed by Jews for almost 3,000 years. But was she really? PERHAPS NOT. She might be surprised to discover that in contrast to their commonly prevalent image as devout and trembling monotheists, many ancient Jews were flouting their own religious laws from just about the moment they were enacted. Isaiah, Jeremiah and Ezekiel all wagged their collective finger at their iniquitous "idol whoring" brethren, warning them of the terrible fates that awaited them for their incorrigible sinfulness. Yet given the centrality of kosher laws in Jewish tradition, it is strange that very little was uttered by any of these biblical prophets about the rampant consumption of unkosher food. The single mention that comes to mind is Isaiah 66:17, a passage near the book's end that was apparently included much later, during the era of the Babylonian exile in the sixth century BCE. The verse bitterly laments the people "eating swine's flesh... and the mouse." No accounting for ancient tastes. But mention of forbidden fish is nowhere to be found. Yet we do know that the prophets' Jewish neighbors regularly ate such creatures. In late 2005, while sifting through the remains of an ancient structure in the City of David just south of Jerusalem's Old City wall, archeologists discovered a hoard of thousands of animal bones. The remains of sheep, goat and cattle are a common find at ancient excavations in Israel, but the sheer amount of fish bones at this site was quite unusual. Jerusalem is, after all, high up in the mountains and far from the sea and large rivers, which would have made fish a very expensive luxury for the city's residents. That fish was widely sold Jerusalem is implied in the Bible: The books of Zephaniah, Nehemiah and II Chronicles all mention the "Fish Gate" which is where the local fish market must have existed. OMRI LERNAU of the University of Haifa, an expert on ancient fish bones, has identified a wide variety of fish at the City of David site, mainly from the Mediterranean and the Nile River. In an e-mail exchange, Lernau explains that for many centuries by then, dried, salted and smoked fish was already being exported from the Nile Valley to the Eastern Mediterranean coast, Cyprus and Turkey. The marketing and processing of fish and fish sauces would develop into a vast trans-Mediterranean business by Greek and Roman times. The trove of bones in the City of David was comprised of several types of fish that were kosher, but also included catfish, a thoroughly unkosher sea creature whose remains have been found in many other excavations throughout Israel, including strictly Jewish towns such as Gamla on the Golan Heights. And if eating unkosher fish wasn't bad enough, Nehemiah, the governor of Judah, complains in the biblical book that bears his name that many Jewish Jerusalemites habitually purchased their pricey fish from Phoenician sailors on the Sabbath day, itself a grave violation of Torah law that was legally punishable by death. Herein lies the problem: Jewish tradition assures us that the Levitical kosher laws were dictated by God to Moses around 1200 BCE, who in turn passed them down to the people. And yet we are faced with a ubiquity of unkosher fish remains at Jewish sites from a period when Jews should have been thoroughly familiar with these statutes for more than four centuries, and would have presumably shunned them. This implies two alternative possibilities: One is that ancient Jews were brazenly violating kosher laws, literally under the noses of the Temple clergy. If this is the case, the general silence of the biblical prophets on this crucial matter is strange, to say the least. The other possibility is that despite the contentions of ancient tradition, kosher laws had not yet been fully promulgated by the ninth-eighth century BCE - the late Iron Age period to which the City of David animal bones have been dated. Either way, the implications leave a great deal of... seafood for thought. What is certain is this: that far from being an iconoclast, my mother-in-law can rest assured that she remains a link in a long line of treif Jews. The writer is a New York-based author and research analyst. He is writing a graphic novel about life and loss on the Lower East Side.