Source: Jewish Holiday Kitchen - Joan Nathan

INGREDIENTS:

One 4-5-pound haddock (fillets, cut and ground), plus the head, skin, and bones-if only smaller fish are available, you can add 1-2 more fillets
2 quarts plus ½ cup water
1-2 large onions, peeled
Several sprigs parsley
6-7 large carrots
5 tbsp sugar
4 tsp salt
Freshly ground pepper to taste 
1 small onion, grated
1 egg
2 tbsp matzah meal or cracker crumbs.

DIRECTIONS:

1. Put the bones, skin, and head of the haddock in a large soup pot. Cover with water to about 2 inches over the bones (about 2 quarts). Add the peeled onions and parsley. Cut the carrots on a slant and add them to the pot. Bring to a boil. Add 4 tbsp sugar' 3 tbsp salt, and pepper to taste. Remove scum and simmer.
2. Meanwhile, grind the fillets and place in a bowl. Add the grated onion, egg, matzah meal, 1 tsp salt, pepper, 1 tbsp sugar, and ½ cup water. Mix well.
3. Dip your hands in cold water and form balls 1½ in diameter (tinier if you want them for appetizers). Drop the balls in the simmering soup and bring to a boil again. Then simmer, covered, for 1 hour.
4. Remove the balls carefully and extricate the carrots. Pour the  liquid stock through a strainer and chill. The bones can be discarded.

For an hors d'oeuvre, serve the tiny fishballs with a toothpick on a round of carrot, using horseradish as a dip. As a first course or summer luncheon dish, serve with carrots, some fish stock, a sprig of parsley, horseradish, and hallah.