Cook the lobsters (or spiny lobsters) in salted vegetable water for about 20 minutes, then let them cool in the cooking liquid.
Meanwhile, tie the catfish into a neat cylindrical roll with kitchen string, and salt it.
Poach gently in a tangy, vegetable poaching liquid (water, vinegar, vegetables, bay leaf, pepper) for about 25-30 minutes, then let it cool in the liquid.
Slice the cooled catfish roll into equal pieces.
Stir the finely chopped tarragon into the melted, lukewarm aspic.
Coat each fish slice with the aspic so it's covered by an even layer at least 2 mm thick; repeat as needed, chilling in between to set.
Carefully extract the meat from the lobster tails from underneath, so the top of the shell stays whole.
Chop the extracted meat finely, mix it with the mayonnaise, and stuff it back into the empty shells.
Slice the stuffed tail shells, and arrange on a platter.
Arrange the aspic-coated fish slices around them, garnishing to taste.
Serve cold with remoulade sauce or mayonnaise.
Based on: Malatinszky Fanny szakácskönyve (a classic Hungarian cookbook), modernised. Calories and protein are estimated.