Every year or so my son decides to cook thai food and buys a bottle of fish sauce.
Look up the ingredients:
"Fish sauce is a liquid condiment made from fish or krill that have been coated in salt"
"Some variants add herbs and spices. For modern fish sauces, fish or shellfish is mixed with salt at a concentration of 10% to 30%"
There can be sugar in it as well, or other sweeteners.
The salt alone already would be reason for me to not want to use this.