Fish stock, also called fumet, is a simple way to add savory seafood taste to your recipes. It is the base for many sauces, soups, and seafood dishes. Fish stock can be an integral ingredient for making bouillabaisse. It is made from simmering the bones and heads of non-fatty fish, like halibut or other white fish. The resulting stock is a clear liquid, with a delicate, but unmistakable fish flavor.
Using a fish with fatty meat may result in a stock that produces gelatin, which can be skimmed off the top if not used in the dish. Fish stock can be a little harder to find at the grocery store than beef, chicken, or vegetable stocks. If you are unable to find it, have a seafood allergy, or do not eat fish, select a fish stock substitute and keep cooking!
List of Fish Stock Substitute
Select the best fish stock substitute for your recipe from alternatives like bottled clam juice, vegetable or chicken broth, dashi, and other seafood like shrimp, crab, and lobster shells. 
Bottled Clam Juice
Clam juice is a popular and easy substitution if you cannot make your own fish stock. Buy two or three bottles, depending on how much stock you need. Boil the juice with half a vegetable bouillon cube in an uncovered pot until the liquid has reduced by 25%. This can give you a similar concentration of flavor while keeping the liquid light and clear.
For a faster, lighter flavor, you can mix equal parts of clam juice and vegetable broth without reducing the amount of liquid.
Half a cup of chicken broth or half vegetable broth, mixed with half a cup of water, will work as a great fish stock substitute. Cutting the broth with water can stop the flavors of seafood in the dish from getting muddied since both chicken and vegetable broths can be very strong and salty.
Alternate Fish Stock
If shellfish is not an issue, the fish stock can be made using other seafood as well. A simple shellfish stock can be made with shrimp, crab, or lobster shells, some vegetables, and a bit of white wine.
Dashi is a traditional Japanese fish stock made with bonito fish flakes, used in many miso soup and noodle dishes. A vegan version of dashi can be made by making a stock out of dried kombu kelp and shiitake mushrooms. It may not taste like seafood, but it will give the dish savory depth and sea-like saltiness.