Preheat a water bath to 110°F (43°C).
Remove the pin bones and skin from the salmon. Sprinkle the salmon with the citrus zest. Combine the salt and sugar together in a small bowl then sprinkle some over the salmon, there will be some left over. Place the salmon in the sous vide bag and lightly seal. Let the fish sit in the refrigerator for at least 30 minutes but preferably several hours or overnight for the dry brine to take effect. Place the sous vide bag in the water bath and cook for 15 to 45 minutes, until heated through.
For more information on the cooking times you can read my detailed article which addresses why is there a range in sous vide cooking times.
Once cooked, remove the sous vide bag from the water bath and place in an ice bath until chilled.
Remove the root of the fennel. Remove the fronds and reserve them, then thinly slice the fennel.
Add the orange juice, lemon juice, and olive oil to a bowl then whisk to combine. Add the fennel and toss to coat.
Add the onion, red wine vinegar, water, and sugar to a pot and bring to a boil. Reduce the heat and let simmer for 5 minutes. Remove from the heat and let cool.
Take the cooked and chilled salmon out of sous vide bag and pat dry. Thinly slice the salmon.
Place some of the fennel carpaccio on a plate along with its dressing. Top with several slices of salmon. Add some capers then sprinkle with the citrus zest. Top with some fennel fronds and pickled red onion. Sprinkle with sea salt then serve.