Scale, fillet and skin the salmon trout. Remove the line of small bones that runs down the middle of each fillet using a pair of pliers. Cut each fillet slightly on an angle into six pieces.
Peel the asparagus and tie in bundles of six. Cook in boiling salted water so that they are cooked but still retain a little bite. Refresh in iced water and drain.
Blanch and skin the tomatoes, then deseed and cut the flesh into small dice. Mix together the oil and the sherry vinegar and add the tomato. Tear the basil leaves into small pieces and add to the vinaigrette. Season to taste.