A 29-year-old former hedge fund manager has managed to raise the initial public stock offering ever in the biotechnology industry.

The successful market debut of Axovant Sciences renewed concerns that biotech stocks, which have outperformed the overall markets for several years, are now in a bubble.

It has been said that Axovant raised $315 million in its offering Wednesday, selling 21 million shares at $15 each. It was 3.1 million more shares than it had expected to sell and at the high end of the expected price range.

The amount even exceeded the $264 million funds raised in December by Juno Therapeutics, which at the time was believed to be the largest I.P.O. in biotechnology, at least in the United States.

Shares of Axovant at the first day of the trading on Thursday nearly doubled to close at $29.90.

The 29-year-old founder of Axovant, Vivek Ramaswamy, had previously managed a biotech hedge fund, when, he said, he got the bug to do it himself.

Ramaswamy said, "I really was inspired by the possibility of more directly being involved in the development of drugs myself".

In last May he started a company called Roivant Sciences, which in October created Axovant as a subsidiary to develop drugs for dementia.

Axovant said that later in this year it will start another trial testing the drug, which it calls RVT-101, with donepezil, the generic version of Aricept.

Ramaswamy, who earned a bachelor's degree in biology from Harvard and a law degree from Yale, said he did not consider his company's offering a sign of a bubble.