Talk of koi carp reminds me of a story from one of Jeremy Clarkson's books, talking about pet fish becoming more popular than dogs ...
They don’t come when they’re called, they don’t bark at strangers, they won’t fetch sticks, they’re not cute and, being fairground goldfish, I’m fairly sure they wouldn’t be delicious either. Honestly, it’d be more rewarding to own a pet rock. And don’t think things improve if you move up the evolutionary scale and go for a koi carp. My dad did that, and spent many happy hours watching them gliding around his garden pond, gorging on the psoriasis flakes that fish call food. Then one Christmas I bought him half a dozen ‘ghost koi’ which looked very splendid in the tank at the pet shop. Unfortunately, in my dad’s pond we learnt why they are called ‘ghost’ fish. It’s because they are completely invisible. And what’s the point of a pet you can’t see? Sadly, I also discovered that in the fish world they are the SAS among carp, approaching their prey silently and killing without pity or remorse. So within a day, all my dad’s beloved orange fish were upside down on the surface, leaving him with a pond full of apparently nothing at all. My advice, then, is simple. If you want a fish, get it from the chip shop.