First de-bone the fish, the fish is described below. Lay the fillets flat, skin side down, on a large plate, sprinkle with the salt and pepper, and refrigerate until ready to cook. Now make a fish stock by placing all the boning-process trimmings in a saucepan on medium-high heat with the water, celery and mushroom stems. Cook for 25 minutes. Strain and set aside. Cut the celery heart in two lengthways and place in a microwave dish. Pour in 1 cup of the reserved fish stock, cover, and cook on high power in the microwave for 10 minutes. Turn the celery over, rotate the dish 45 degrees and cook for 5 minutes. Remove the celery and set aside, reserving the liquid. Slice the mushroom caps thinly and add to the strained fish stock, cover, and microwave on high for 3 minutes. Strain out the mushrooms; reserve the liquid. Press the mushrooms on the fish fillets; sprinkle with the shrimp and dill. Pour the reserved fish stock into the microwaveable dish, just large enough to hold the trout. Carefully lift the prepared trout into the stock; the liquid level should just reach the top of the fillets without covering them. Cover with greaseproof (waxed) paper and cook on high in the microwave for 4 - 6 minutes, depending on the size of your oven. Transfer the fish to a serving plate and keep hot. Saffron sauce: Use the poaching liquid and enough reserved stock to make 2 cups of poaching stock into a small saucepan, stir in the saffron, and heat through. Make a slurry of arrowroot and water and stir this in to thicken just to the consistency of melted butter - about 1 minute. Add the lemon juice to taste. Steamed rice: Bring water to a boil in a medium pan. Add rice and salt; boil 15 minutes. Strain in a metal sieve; put the rice-filled sieve over a pan of boiling water and steam, covered, for 5 minutes. To serve: Drizzle the tender trout with the golden saffron sauce and present to your guests with the celery heart and rice on the side.