According to Wikipedia, ketchup originated “In the 17th century, [when] the Chinese mixed a concoction of pickled fish and spices and called it (in the Amoy dialect) kôe-chiap or kê-chiap (鮭汁, Mandarin Chinese guī zhī, Cantonese gwai1 zap1) meaning the brine of pickled fish (鮭, salmon; 汁, juice) or shellfish.”
As a kid, I spent a lot of time at drugstore lunch counters. Many of you are no doubt too young to remember those; every drugstore had one. You could get made-to-order Coca Cola from a spout that mixed the syrup with fizzy water right in front of you (flavors, from cherry to chocolate and vanilla, were optional), various ice cream treats (malts, shakes, floats and sundaes), more or less fresh coffee and donuts, and greasy lunches for a reasonable price. Condiments like salt and pepper, mustard and ketchup, were lined soldier-like along the length of the counter. It was a cheap hangout, an ersatz clubhouse, where a guy too young to hang out in a bar could go and reasonably expect to find a friend or two any time of day. Best of all, magazines and comic books were always displayed nearby, and you could sit and read them without buying; the proprietor generally only complained a couple of times a month, when the racks got overly disorganized, as long as you were careful not to treat them so roughly that they couldn’t ultimately be sold.
A kid could get to know the routines: the shift changes, the making of the Fresh Coffee (older customers timed their arrival for this), and the refilling of the condiments. I would sit and watch, fascinated, as the counter server went from container to container, topping off the bottles and shakers. I never saw anyone empty and wash out a bottle of ketchup, which leads me to one inescapable conclusion.
Some small trace of that original 鮭 was no doubt still at the bottom of those ketchup bottles, and that’s why I have such a strong immune system to this day.