The BarclayHedge cryptocurrency traders index was up 138.1% for 2021, according to data the firm posted on Friday, showing results for about 39 funds, or less than 50% of the digital asset management firms it tracks. That followed record gains of 173% in 2020, as crypto funds benefited from extreme volatility that the coronavirus pandemic stoked across financial markets.

Bitcoin gained 60% in 2021 as it hit a record peak of $69,000 in November, while ether, the token used for the Ethereum blockchain, surged roughly 400%.

"There is an air of legitimacy now. Bitcoin is no longer viewed as an esoteric digital currency used only on the fringes by techies and cypherpunks," according to CoinDesk's annual crypto and blockchain review for 2021.

For the month of December, however, crypto funds showed losses of around 11%, as bitcoin and ether slumped as well. Bitcoin dropped 19% last year, while ether fell 20%.

"Crypto was the only sub-sector that didn't make money in December, as many of the industry's headline assets suffered whiplash from a sharp price downturn," said Ben Crawford, head of research at BarclayHedge.

Crypto's more traditional cousin, foreign exchange, on the other hand, turned in modest returns in 2021.

BarclayHedge's currency trader's index showed a gain of 2.2% last year, based on 60% of funds that reported. Currently there are 40 FX programs tracked by BarclayHedge.

The 2021 gain for FX funds followed a 4% rise in 2020. Returns were subdued last year as global central banks kept a lid on interest rates, depressing volatility.

Currency funds' returns, meanwhile, showed an anemic 0.23% rise in December.