Research update: Goldfish and water quality

Summarized Krishona Martinson, Ph.D., University of Minnesota
Farm Forum

Goldfish have been reported as a method to keep water tanks clean; however, little information exists on this approach. The objectives of this research, conducted at the University of Minnesota, were to evaluate the efficacy of goldfish on maintaining water quality in tanks and to evaluate the frequency that this method is used.

The first objective was completed during June through October 2017 in St. Paul, Minn., using plastic and metal 100 gallon stock tanks, each with and without goldfish in a drylot that housed six adult horses. The stocking rate was 5 goldfish per tank. Daily readings of total dissolved solids (TDS) and water turbidity (NTU), and weekly samples to measure chlorophyll a were taken. At the end of each 28-day period, tanks were cleaned and rotated. Plastic tanks had lower TDS than metal tanks; however, metal tanks had lower NTU and chlorophyll a. Adding goldfish resulted in lower TDS; however, there was no effect on NTU or chlorophyll a. No parameters had an impact on horse preference.

The second objective was completed using an online survey that was open from October 31 until December 15, 2018. Of the 672 completed surveys, 56% had not tried using goldfish in water tanks, 26% had utilized goldfish in the past, and 18% currently used goldfish. The inclusion of goldfish in water tanks did not affect all water quality parameters; however, 44% of survey respondents had tried, or were currently using, this management method.

Based on these results, we cannot conclusively recommend using goldfish as a management method for maintaining water quality in stock tanks, and goldfish should not replace frequent cleaning as a way to maintain water quality.