GloFish

I know what kind of fish I'm keen to add to the aquarium, though, as soon as it's established — these are GloFish. I understand these are genetically modified zebrafish (or rather these are descendants of the original genetically modified fish), developed with the intention of indicating the presence of toxins in water. They are literally florescent, and glow under black light. They look really nifty under ordinary light, too.

Many years ago, my wife was talked into buying some transparent Glass Catfish with beautiful streaks of vivid color — only to learn, to her horror, that the fish had been injected with a small amount of dye to create that effect. Since then, we've been careful to avoid those kinds of fish, no matter how beautiful they appear.

(Thankfully, GloFish are born to brilliant color.)