# How many dead fish get flushed down the toilet a year?

Ha! This is what we might call a Gedanken thought. That is: it’s an interesting question as a start for a discussion, but it isn’t likely we’ll find much of a definitive answer.

First of all, I would want to know whether you really meant: How many people flush live fish down the toilet. Then we could start our discussion.

The way to “solve” problems such as this is to break them down into pieces. Here are some pieces:

•  What percent of people in the world own toilets? It’s not everyone, that’s for sure.
• What percent of people own tropical fish? (I assume that’s what you mean.)
• How many fish do they own?
• How many of those die?
• How many owners just get fed up with cleaning the algae from the glass, and decide to ditch the whole fishtank?
• How many of those people decide to use the toilet, rather than say, dumping them in a river, lake or ocean. (Or backyard fishpond.)

Having broken the question into reasonable sub-problems — feel free to add your own — I can then make a guess without consulting the Internet.

I guess only 1/3rd of people in the world have toilets at home. So that makes, say, 2 billion. An average household is say 4 people. That makes 500,000,000 households. Of those, maybe only 1-in-10 has tropical fish. That makes 50,000,000 households with tropical fish. Of those, probably many are just fishbowls with a goldfish or a guppy enjoying the good life. So the average number of fish is maybe 200,000,000.

How many adult fish die a year? Well, on the average 200,000,000. But a big part of those are just going to be helpfully eaten by their tank friends. So we’re back down to, say, 100,000,000.

The big uncertainty is: What happens to the other dead fish? In the garbage, or down the toilet? I vote 90% in the toilet. That’s 90,000,000. But we’re not quite finished, because some people are just going to throw the whole tank away at once. Gross, yes, but true. They should at least feed them to a happy kitty and save environmental damage!

Prolly 1-in-5 people abandon their aquarium a year, so to 90,000,000, add 10,000,000 tanks’ worth of fish. (Ok, I cheated with the numbers a bit on this last one, sue me.) So I get 10,000,000 X 4 + 90,000,000 = 130,000,000 fish.

That’s a heck of a lot more than I thought when we started. Gedanken thought experiments can be useful!