Preheat the oven to 350°F (180°C). Place fish mixture in two separate bowls. To one bowl, add chopped herbs and stir, turning it from white to green.
In a non-stick ovenproof mould, arrange the crayfish in a neat pattern, covering the bottom. Gently spread out the white fish mixture over the crayfish, using a wet spatula.
Place asparagus lengthwise on top. Finish with the green fish mixture, spread evenly. Give the mould a few gentle knocks against the table to remove any air bubbles.
Place the mould in a bigger ovenproof dish, and fill the dish with boiling water two thirds up on the non-stick mould. Bake in the oven for 45 to 55 minutes. Check for doneness by poking it with a knife. If it comes out clean, the terrine in done.