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Woody Tews
Title: Breeding the 'Fathead Minnow' Pimephales promelas

Summary: The Milwaukee Metropolitan Sewerage Department uses fathead minnows for experiments and testing of treated sewage water. Woody saw how the laboratory breeds them, and also bred some at home himself.
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Breeding the 'Fathead Minnow'
Pimephales Promelas

By Woody Tews
From Splash, newsletter of the Milwaukee Aquarium Society

The Milwaukee Metropolitan Sewerage Department works with a firm called SF Analytical Laboratories located at 6125 W. National Avenue in Milwaukee to determine when treated sewage can be released into Lake Michigan. In their testing, the laboratory uses 3 creatures or organisms for their test results. They are; algae, tiny daphnia, and fathead minnows. Mr. Jim Stark who is the manager of SF Analytical has provided me with all the technical data regarding their experiments plus a video that he produced. I in turn then will make this material available to our club library for anyone who is interested. All of the procedures regarding this testing were most interesting but I will dwell on the fathead minnow.

The minnow is so named because the males develop a large spongy growth on the top of their heads. This growth helps them protect the eggs from would be predators. The males average about 3 inches in length and the more slender females are about 2". Mr. Jim Stark was kind enough to give me a tour of the laboratory and a comprehensive dissertation regarding all the testing including the spawning of the fathead minnow.

The lab uses 15 gallon tanks divided into quarters with substrate. The substrate used is sections of 4 inch PVC about 4-5 inches in length. The temperature is maintained at approximately 77 degrees Fahrenheit with 16 hours of lighting and 8 hours of darkness. Regular aged tap water works fine although the lab has a well.

For my home experiments I used 10-gallon tanks at 75-80 degrees Fahrenheit with my aged tap water. I used one pair for best results per tank. I never witnessed a spawning because it seemed to occur early in the morning. I have a small window near the spawning area and the natural coming of daylight seemed to be very important. When I would feed the fish, if the males were inside the cave (formed by the substrate) it was usually a sign that they had spawned. The female after spawning left the site to the protection of the male. The eggs were sort of gelatin like in appearance and quite clear. I didn’t count them but I am sure there were on occasion a couple of hundred.

Five days seemed to be the norm for hatching. I would remove the substrate with the eggs and put them in a shallow plastic pan (like they give you in the hospital). The pan would hold about 3 inches of water, and I then floated the pan in a heated 10-gallon tank. In addition I supplied an airstone for water movement along with a few drops of an anti-fungal solution. In the beginning I fed infusoria created by adding dried banana peels to containers with older used tank water. I also fed powdered egg yolk. After a week to 10 days I fed baby brine shrimp and micro worms. When the fry became baby guppy size I released them into the aquarium proper from the pan.

All fish are interesting but knowing the role that the fathead plays in the processing of our drinking water made them appealing to me as a hobbyist. They are quite common in the USA and that is why they are the industry standard for experimentation. Once again on behalf of the Milwaukee Aquarium Society, and myself thank you Mr. Jim Stark of SF Analytical Laboratories in Milwaukee, WI. Also a thank you to Mr. Eric Waldmer of the Milwaukee Metropolitan Sewerage District who mailed me the detailed description of the Biomonitoring testing process.