We’ve all heard it… goldfish keep water troughs free of algae. Sounds great, right? Unfortunately, this is truly an old wive’s tale.

Researchers at the University of Minnesota conducted a study to determine how goldfish influenced water quality. They tested plastic and metal troughs with and without goldfish. They found that goldfish were not the best at keeping troughs clean. The algae content of tanks was unaffected by the presence of goldfish. Water turbidity was also unaffected. Horses drank equally out of tanks with fish versus without fish, however the fish used in the study had a high death rate.

Additionally, 26% of horse owners surveyed had used goldfish previously. Of those respondents, 43% stopped using fish due to high fish mortality, and 22% discontinued use of goldfish because they did not think they were effective.

The study did find, however, that metal troughs had lower turbidity and less algae compared to plastic troughs. So, that is something to think about!

Concerns about animal husbandry were also raised. Is it cruel to keep goldfish in a trough? There are differing opinions on this, but from an animal husbandry perspective, stock tanks are not the ideal habitat for goldfish. So it is not surprising to me to see high mortality for the goldfish in the study and in the survey.

In conclusion, if the goal is a clean trough, it is unlikely that goldfish will make any difference. Some claim that goldfish are quite effective at controlling mosquito larvae. Maybe a researcher out there would like to take that on as their next study?

To read more about the study I referenced, click the link below!
https://extension.umn.edu/horse-care-and-management/cleaning-animal-water-tanks