Whats the difference between Fish oil and Krill oil?

So I was in the vitamin section at the store the other day and saw bottles of Fish oil and Krill oil. I thought Krill was a type of fish so wouldn't Krill oil and fish oil be considered the same thing? Does one work better than the other? What are its benefits? From your own personal experience what did it do for you? Is is worth taking in your opinion?
Whats the difference between Fish oil and Krill oil?
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