What is Fish Sauce?:
Fish Sauce, or "Nam Pla" in Thai, is one of the basic ingredients in Thai cooking. It has a rich translucent reddish-golden brown color, and is used liberally in nearly all Thai dishes. It is often used as a marinade for fish and meat, as well as a condiment (usually mixed with fresh-cut chilies and lime juice) - you may have come across this "sauce" on tables in Thai restaurants. In fact, Thais would add a little fish sauce to their meal the same way we would use salt and pepper.
What is Fish Sauce Made of?:
Good fish sauces are made from a mixture of fish and salt that has been allowed to ferment for 1 year to 18 months. Anchovies are typically used, although some fish sauces are also made from other types of fish or squid. The basic ingredients of a good fish sauce are: fish, water, and salt. Sugar may also be added, but isn't necessary.
Where Can I Buy Fish Sauce?:
These days, most supermarkets sell fish sauce (look for it in their Asian section). Personally, I have found the best type is usually sold in Asian food stores. You'll find a good selection of fish sauces at nearly any Chinese/Vietnamese/Thai food store. Look for tall bottles with "Fish Sauce" and the ingredients displayed on the label (fish extract, salt, and water - other ingredients aren't necessary). It should be made in Thailand or Vietnam. You can also order it online. Squid Brand Fish Sauce is a good one.
What Can Vegetarians use as a Substitute for Fish Sauce?:
Vegetarian fish sauce does exist. So far I've yet to find it in a Thai food store, but nearly all the Vietnamese food stores carry it. Better substitutes (in my opinion) are Golden Mountain sauce , or just plain soy sauce. When I cook Thai for my vegetarian sister, I use a combination of these two sauces, and the food always turns out wonderfully. For Golden Mountain Sauce you will need to shop at a good Asian food store (see link for more on this 'secret' Thai ingredient).
Fish Sauce & Sodium: What to Do if You're Worried About Salt Intake?:
For those who are concerned about their sodium intake, using fish sauce can be a bit of a dilemma. Not to worry. While the sodium content of fish sauce seems outrageous when you look at the serving size on the label, remember this amount will be distributed throughout the dish you're cooking (for example, a Thai curry), so you won't be consuming all of it - at least not in one portion or sitting. Add only a portion of the fish sauce called for in the recipe, then top up the remainder with sea salt. Sea salt has only a portion of the sodium found in regular table salt, and is much better for you in other ways too.
How do I keep dishes made with fish sauce from smelling 'fishy'?:
Here's the secret: lime juice. In most Thai recipes you will find fish sauce paired with lime juice and other ingredients. I always tell people it only smells fishy to use, as the cook, because you were the only who added the fish sauce (and had to smell it). Personally I don't mind the smell at all, but perhaps I am now so used to Southeast Asian cooking that it has become a normal part of my sensory world. In any case, if you find either the dish you're cooking OR your hands smelly 'fishy', try squeezing over some fresh lime juice and see if it helps. Cheers!