Like the river it's named for, Amazon never stands still. Nor can it afford to: Though the world's biggest online retailer has proved remarkably...

Like the river it’s named for, Amazon never stands still. Nor can it afford to: Though the world’s biggest online retailer has proved remarkably recession-resistant over the past few years, its efforts to stay abreast of ever-evolving technology have landed it a whole new set of tough competitors.

Not that that’s anything new for Amazon. When the company launched its bookselling website 15 years ago, few thought it would ever pose much threat to giants such as Borders and Barnes & Noble. Now both those retailers are struggling to stay afloat.

A few years later, when Amazon expanded into consumer electronics, the biggest names in that field were Circuit City and Best Buy. Circuit City went bust last year and closed all its stores; Best Buy remains a formidable competitor.

To look at Amazon’s financial results, you’d never guess there was a recession on. Sales in fiscal 2009 were $24.5 billion, up 27.8 percent; profit was up nearly 40 percent. The company’s first-quarter results this year were similarly strong.

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Amazon’s biggest shift has been its Kindle e-reader, the first version of which was released in late 2007. The company still refuses to say how many Kindles it has sold, though the technology news site TechCrunch estimated total sales at 3 million as of the end of 2009. Whatever the number is, it’s likely to grow now that Target will start selling Kindles in selected stores.

That may or may not have anything to do with Apple’s launch earlier this year of the iPad, which is an e-reader among many other functions. Barnes & Noble has its own e-reader, the Nook; Google reportedly plans to launch one later this year. Suddenly there are a lot more piranhas in the water.