Clean the carp, reserving the bones and the head. Slice the carp and the catfish into large pieces, sprinkle them with salt, and set aside. Place the carp bones and head and all of the small fish into a large pot. Add the onions, and pour 10 litres of water to cover. Add some salt, bring to a boil, and boil continuously for at least 40 minutes. Remove from heat and add paprika. At this point, a chopped tomato and pepper can be added, if desired. Return to the heat, bring back to a boil, and simmer for ten minutes. Push the soup through a sieve to make a dense broth. Bring the broth back to a boil and add the pieces of carp and catfish, cooking the soup at low heat until all fishes are soft. For this type of fisherman’s soup, noodles do not fit; serve with fresh bread instead.