What place to goldfish have on a farm, or in a garden? 

how many people are out there who started collecting rain water to irrigate with?

Goldfish will keep such containers free from mosquitoes

fish water

is loved by plants

fish excrete their waste nitrogen in precisely the form most available to plants, and it's dilute, so you can just pour it on. 

But really, I just like goldfish. They are so pretty, little reflective jewels gliding through the water.