The Swiss bank says Crossfinder has experienced steady volume growth this year and is now the number one dark pool in the US. The bank cites research from Rosenblatt Securities which shows the ATS represented 1.55% of US stock trading volume in September.

Crossfinder was launched in 2004 but has seen volumes boosted over the last year after a concerted effort to attract retail investors.

Dark pools that are operated by banks - like Crossfinder - have come under fire recently, with the the World Federation of Exchanges voicing concerns that they do not come under the same scrutiny as platforms run by bourses.

Earlier this month five firms that operate off-exchange venues moved to placate critics by agreeing to print trades made on the venues on the reporting facility Nyse Euronext operates with Finra and display daily activity on Nyse.com. Credit Suisse was not one of the five operators.

However, not all exchanges are hostile to bank-owned platforms. London Stock Exchange CEO Xavier Rolet has defended dark pools in a Bloomberg interview, claiming the help market stability. Rolet says enabling stocks to be traded off-exchange prevents volatility caused by large movements of assets.

Rolet recently pulled the LSE out of the Federation of European Securities Exchanges (FESE), which has joined the criticism aimed at dark pools run by bank.

Facing ever-growing competition from upstart European exchanges, he wants to work with banks, notably on the LSE's Baikal dark pool. According to the Financial Times, the bourse is close to a deal that would see Baikal merged with the bank-owned Turquoise trading platform. No money would change hands but the LSE would hold a 51% controlling stake in the merged entity.