Both fish and oyster sauce add umami flavour to Thai food and are key ingredients in this cuisine. If you have Worcestershire sauce on hand instead of these, you can try it in your Thai recipes. If you’re a vegetarian, you can use an oyster sauce substitute that’s made with mushrooms. If you want to leave the sauces out altogether, add extra salt to make up for the lost saltiness. Soy sauce can be the perfect substitute for both salt and flavour.