By Paul R. La Monica, CNN Business

(CNN) -- Aurora Cannabis, one of the biggest Canadian marijuana stocks, debuted on the New York Stock Exchange Tuesday and it didn't go well. Shares quickly fell more than 15% before recovering towards the end of the day.

Many of Aurora's marijuana peers were tumbling sharply, too.

Investors have been dumping cannabis stocks since Canada legalized recreational marijuana last week. It's a classic case of buying the rumor and selling the news, as many of them surged in the past few months.

Shares of Canopy Growth (CGC), Cronos (CRON) and Tilray (TLRY) all fell about 10% Tuesday at one point. And each of them are down about 30% in the past five days.

But Canopy Growth, which has a more than $4 billion investment from US beer giant Constellation Brands (STZ), has surged more than 50% in the past three months.

Aurora (ACB), a company that has diverse operations throughout the cannabis industry -- it's been dubbed by some as the Berkshire Hathaway of pot -- has been just as volatile.

The company's shares, which also list in Canada, have fallen 30% in the past week although they're still up 45% in the past three months.

Of course, it doesn't help that the broader market has tanked in October because of concerns about slowing earnings growth and a trade war with China.

But Canadian cannabis companies already may be running into concerns about over-saturation. How many cannabis companies does the world really need?

Toronto-based credit rating agency DBRS put out a report Monday that was skeptical of many of the big Canadian marijuana stocks.

Analysts at DBRS said that "for now, cannabis is still a relatively small-scale subsector within the context of the consumer products industry and the economy in general" and added that "not all will perform equally and many will fail."

That sounds an awful lot like internet stocks in the late 1990s. At that time, online shopping was a very small part of the overall retail pie. But companies were falling over themselves to set up e-commerce sites.

Marijuana -- both for recreational and medical purposes -- may eventually become a major business. But not everyone will become the Amazon of pot. More companies will lose than win.

Terry Booth, CEO of Aurora, is bullish though.

He said in a release about the NYSE listing earlier this month that Aurora intends to "meet the growing demand for high-quality cannabis both in Canada and abroad" and is also working on "scientific research into medical applications of cannabis."