Steam the potatoes whole for 20 minutes until tender. Insert a knife to check that they are soft in the middle. Mix the chives and red onion with the crème fraîche and seasoning.
While the potatoes are cooking, heat the oil in a pan and cook the sea bass fillets for 4 minutes on each side.
Slice the potatoes while still hot and mix with the crème fraîche and chive mixture. Serve