Peel and quarter the carrot and onion.
Combine the water, bouquet garni, peppercorns, 1 tsp (5 ml) salt, the cloves, carrot, and onion in the bottom of the steamer and bring just to a boil. There should be about 2 inches (5 cm) of court bouillon in the steamer.
Simmer 20-30 minutes.
Meanwhile, rinse the fish fillets with cold water; pat dry with paper towels.
Discard any bones.
Trim the fillets so they are roughly the same length.
Cut each of the fish fillets lengthwise into strips about 2 cm (3/4 inch) wide, so that there will be 6 strips of each different type of fish to plait. TAKE CARE: Handle the fish gently while cutting so strips do not break.
Arrange a strip of snapper, sole, and mackerel next to each other, skin-side up.
Plait the strips together, lifting them carefully over each other and gathering the ends together.
Continue making plaits with the remaining strips of fish.
Plait strips loosely so they do not shrink and break during cooking. Don't worry if the plaits are not even.