The Darwin Fish is a symptom of the larger square- peg-in-round-hole disease that seems to afflict the 'Brights'. Look, I like science as much as the next guy -- natural selection is true, informative, very cool. But it's not a meaning-giving philosophy. Christianity (or Buddhism, or Islam, or humanitarian Aristoteleanism) tells you how to live your life. Darwinism, or 'science,' or atheism don't do this. It's like making a hobby out of disliking stamp collecting.
It's true that I'm sometimes overly dismissive of those so-called "meaning-giving philosophies." It's just that I've never been clear on what meaning is (like, does it imply signification?) and what it could mean for something to give it. For example, those tens of thousands of people who name "Jedi" as their religion on census forms -- who am I to say that they shouldn't live their lives by the teachings of Yoda? I'm a scientist and an atheist (more or less), so my life must certainly be without meaning. I probably just need more midichlorians.
Well, I think Jedi-ism, while goofy, could qualify. But I didn't mean to judge the plausibility of the foundations (although, as ogged will tell you, I'm very pro the plasuibility of foundations). Rather, let me simply note: people do, in fact give certain species of reasons for their actions. If I ask you why don't you steal your colleagues' work, "because I'm a christian" or "because it's immoral" or "because it will decrease my utility" or "because I'm afraid I'll be caught" are all candidate answers that make sense in a way "because natural selection explains speciation" does not.
Again, just to repeat: I'm a big fan of modern life science, in fact, it's my livelihood. But there are some things we just can't ask it to do, and serving as an ethical theory or religion is not one of those things.