Exchange Traded Funds, commonly known as ETFs, have gained immense popularity in recent years. They give investors exposure to entire industries or sectors with stock-like liquidity, and they are often preferred to mutual funds because fund managers do not take fees out of the total return.

Nowadays, there’s an ETF for just about anything. Here are some of the strangest, most specific ETFs out there.

Global X Social Media Index ETF ($SOCL)

Captures the performance of social media companies. SOCL has all the biggest names in social media like Facebook (FB) , its largest holding, and LinkedIn (LNKD) , its fourth largest holding. However, SOCL also holds companies like Google (GOOG) , Groupon (GRPN) , and Pandora (P) , which aren’t social media companies by definition but certainly have social elements. Half the fund’s holdings are American equities, with China and Japan consuming a combined 39 percent.

Market Vectors Gaming ($BJK)

Seeks to reflect the performance of the gaming industry, specifically gambling. Its largest holdings are Las Vegas Sands (LVS) , Sands China, and Wynn Resorts (WYNN) . The ETF typically pays a cash dividend at the end of the calendar year, yielding 3.93 percent at the end of 2012.

Global X Fishing Industry ETF ($FISN)

Designed to reflect the performance of the fishing industry. Over 40 percent of its holdings are Japanese and its largest holding is Toyo Suisan Kaisha (TSUKF) , a $3.42 billion Japanese food manufacturer with an enormous seafood division.

iPath Dow Jones-UBS Livestock Subindex Total Return (COW)

Reflects the returns of potential investments in livestock futures contracts. In other words, when the price of cows and pigs increases, this ETF tends to perform well. This gives potential investors exposure to investing in animals, and requires slightly less upkeep than actually purchasing a real live animal.

Global X Lithium ETF ($LIT)

Holds the largest companies that are engaged in the exploration and mining of lithium, as well as lithium battery producers. FMC Corp (FMC) , a diversified chemical company with a large lithium business, is by far the ETFs largest holding, capturing 23 percent of total holdings.

Special Mention: Bitcoin ETFs

Two parties have filed with the SEC to create two separate publically traded Bitcoin ETFs. One is SecondMarket, a private investment firm that has already raised $65 million in Bitcoins. The other group is Cameron and Tyler Winklevoss, the twins who are commonly known for their role in the creation of Facebook.

Bitcoin, a controversial crypto-currency, trades wildly. Now selling for above $800, the price of a Bitcoin can swing hundreds of dollars in a single day. Traders would certainly love a piece of the action, and an ETF would be a great outlet to trade it.