Some good combinations:
If using whitefish, mushroom or vegetable stock works well, plus onion, carrot, daikon, spring onion, and mushrooms. For the cream I normally use the evaporated milk.
If using clams or oyster meat, with the juice they come in, chicken or vegetable stock work well, plus onion, carrot, and potatoes. For the cream I normally use the evaporated milk.
For a seafood type chowder, go with a mushroom or vegetable stock, and a little of each seafood listed, plus onion, carrot, potato or daikon. and mushrooms. For the cream I normally use the evaporated milk.
Let's get started. In a medium size pot, heat the bacon fat or butter, when hot, add the onion and saute until softened and starting to brown up.
Add the stock of your choice, the carrot, and 1-3 vegetables of your choice and bring to a boil then reduce to a simmer. As that is simmering add the fish or seafood of your choice, then add the evaporated milk or cream and milk, season with salt and pepper as desired. If using mushrooms add those as well.
Simmer for about 15 to 20 minutes to cook the seafood through and the carrot, and potatoes or daikon are tender.
Ladle into bowls and enjoy.