Aquaculture America 2023

February 23 - 26, 2023

New Orleans, Louisiana USA


Barbara I. Evans, Derek D. Wright, Benjamin J. Southwell and Emily Hebert

College of Science and the Environment

Lake Superior State University


We have been operating two aquaponics systems continuously for nearly three years, one with Koi and another with Tilapia. Water quality has been monitored on a regular basis using the API freshwater test kits and drinking water tests strips. Note, we use aged municipal water sourced from Lake Superior, so the source water has very few ions. Although all water quality parameters appeared within optimal levels, we suddenly lost two Koi fish. Ammonia levels had increased slightly, but other metrics appeared normal. Our analytical chemistry colleagues offered to run water samples using their Inductively Coupled Plasma Mass Spectrometry (ICP-MS) equipment, and were surprised to find high levels metal ions at least an order of magnitude higher that the source water. We decided to shut down the system and moved all fish to another location (where they are doing well). We recently restarted the system with yellow perch, and take regular water samples to see if the metals are accumulating from the food or other contaminants such as condensation from overhead pipes.

Six months after the Koi mortality event we started losing our large Tilapia. Although the pH was low, no other parameters looked out of line. Water samples were again run on the ICP-MS and high levels of metals were found again. Although not as high as those from the Koi samples, several were in the range of chronic toxicity. Comparing our data to chronic and acute levels from the NOAA Screening Quick Reference Tables (SQuiRTs) suggests levels of Aluminum and Copper may be a factor in the fish mortality (Figure 1). However, we did not see any evidence of fish stress, such as gasping at the surface or erratic swimming prior to the mortality.

Our results suggest that caution should be taken with closed loop systems and recommend testing water for metals on a regular based. Although not all aquaculture facilities have access to an ICP-MS; a number of labs will analyze samples. We are still not sure of the sources of these metals as the Tilapia food is different from the Koi food, and our source water has very few ions. Copper levels may be high due to copper pipes, and vary with residence time of the water in copper pipes. We regularly remove water from the system with the solid waste and replace with aged water, so are surprised that we have an increased concentration of these metal ions. We plan to test all feed samples for contaminants, and will also look for other contaminant sources.