It may be better to clean your horse’s water trough more regularly than try novel methods to keep it clean, if a recent US study is anything to go by.

Large water troughs tend to accumulate algae over time if not cleaned regularly. They can also become a breeding ground for mosquitos.

Adding goldfish to water troughs is popular in some places, with the little swimmers thought to slow the build-up of algae, and possibly help control mosquitos by eating the larvae.

A recent survey in the US of 672 owners or horse carers found that 44% had used fish to keep trough clean at some time, and 18% currently used goldfish in their horses’ water.

The survey formed part of a study by Devan N. Catalano and colleagues at the University of Minnesota.

Devan N. Catalano. [Image: LinkedIn]

Six adult horses were kept in a drylot which contained large (379L /100 US gallon) plastic and metal water tanks. Five fish were placed in one tank. After a month the tanks were cleaned, and the fish moved into the other tank.

During the study, the research team monitored the water quality daily, recording total dissolved solids (TDS) and water turbidity (NTU). Once a week they measured the water chlorophyll-a content (the pigment responsible for the green colour of algae).

They found some differences in water quality between the two types of water tank. TDS was lower in the plastic tank, but the metal tank had lower turbidty and chlorophyll-a.

Tanks containing goldfish had lower total dissolved solids, but there was no other difference in water quality between tanks with or without fish.

Horses appeared to have no preference for either type of water container, or for the presence or absence of fish.

The researchers conclude that “goldfish do not improve water quality except for total dissolved solids.” They add: “frequent cleaning is important, especially in warm months and with plastic tanks.”

The full study team comprised Catalano, Bradley J. Heins, Marcia R. Hathaway, and Krishona L. Martinson, all from the University of Minnesota’s Department of Animal Science in St Paul, and Shahram Missaghi, who is with the University of Minnesota Extension, in Farmington.

The Effect of Goldfish (Carassius auratus) on Water Quality in Horse Stock Tanks. Catalano DN, Heins BJ, Missaghi S, Hathaway MR, Martinson KL. J Equine Vet Sci. (2019) 79:73-78. 

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