David Ballois, v.p. in credit derivatives trading at Credit Suisse in London, has left the firm. He had been at the house for two years and reported to Eraj Shirvani, head of European sales and trading in London, who was unavailable for comment. Rebecca O'Neill, spokeswoman in London, confirmed the departure, declining to comment on a replacement. Ballois could not be reached and it could not be determined if he has taken a new position.