SHANGHAI (Reuters) - Chinese hedge fund managers parried criticism of their trading techniques and market impact on Tuesday, a day after the country's top securities regulator said the rapidly growing number of "quants" was a challenge to stock exchanges. Yi Huiman, chairman of the China Securities Regulatory Commission (CSRC), said on Monday bourses should be paying attention to a surge in quantitative trading on the mainland. Quants, as traders and funds that engage in such trading are known, employ fast computers that use mathematical and statistical analyses to trade.