BlackRock filed with the U.S. SEC after the U.S. stock market closed Monday to add bitcoin ETF exposure to its Strategic Income Opportunities Fund portfolio, a public regulatory filing showed. "The fund may purchase shares of exchange-traded products (ETPs) that are designed to generally reflect the performance of the price of bitcoin through direct holdings of bitcoin (bitcoin ETPs), including bitcoin ETPs issued and managed by affiliates of BlackRock," the filing said.