Even if they can both be used interchangeably in dishes, these two sauces are not the same. The Worcestershire sauce is a cousin to the fish sauce and soy sauce as it also provides your dish with an umami flavor. Worcestershire sauce is not as popular as the fish sauce, even if it is mostly available, so you should note that when you need either your fish or soy sauce for a dish and you have none available, you can use the Worcestershire sauce.