In a saucepan, add the onion, 2 carrots, celery, bay leaves and peppercorns. Cover with cold water and bring to the boil. Add salt to taste. Reduce heat, cover and simmer 25 minutes. Strain into another saucepan.
Add the potatoes and carrot to the stock and simmer 10 more minutes.
Add the fish fillet (without thawing) and simmer 5-7 minutes. Serve, distributing the fish equally, garnished with dill.