Put a small-sized fish, onion and parsley in a saucepan, pour in 2 liters cold water, bring to the boil, skim off the foam and cook for 30 minutes. The fish should be overcooked. Then strain the broth and throw the fish away. Cut northern pike, pike perch and salmon into large pieces and boil in the broth for 15-20 minutes, skimming off the foam. Peel potatoes, cut into small pieces and add to the broth; cook for another 10 minutes. Season with salt, pepper, bay leaf and remove from fire. Leave the soup under the lid for 10 minutes. Pour in the vodka and divide between bowls. Add finely chopped greens.