Peel carrots, potatoes and onion, dice finely, place into a saucepan, add thyme, bay leaf and broth. Cook on low heat for about 20 minutes. Peel the fish, finely slice, sprinkle with lemon juice and salt. Cut champignons. Add fish fillets, champignons and crab meat in 20 minutes before doneness. Serve with sour cream and chopped dill.