I disagree that it's actually redundant. It's like if back in 2004 somebody said "Apple computers are overpriced and underpowered." Technically, "Apple" in that sentence stands for "Apple Computer," so you're saying "Apple Computer computers are overpriced and underpowered." But that's fine, because it's just part of the company's name, not actually a redundancy. No copy editor would have flagged that, but they would have flagged attempts to remove the redundancy by saying things like "Apples" or "Apple Computers." Similarly, Fish is a name, so adding "shell" is useful in identifying the thing you're naming.