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Larry's Letters: Trouble with Brine Shrimp

Larry Malone, Co-Director of FOSS, Lawrence Hall of Science
March 08, 2005 | Observations by Larry

On November 11, 2004, I received this letter from Mrs. Mary Martin's fifth-grade class in Spokane, Washington, regarding Investigation 5, Hatching Brine Shrimp, in the Environments Module. The letter came right to the point— the brine shrimp eggs didn't hatch, and she and her students wanted to know why.

Letter

Right away I suspected that the cause of the problem was not the environmental conditions provided by the students, but the viability of the brine shrimp eggs. I dropped the students a note, suggesting that the information they found on the Web probably applied to culturing brine shrimp and raising them to maturity.

The inquiry from Adams Elementary was perfectly timed. We had recently found out that the suggested saltwater recipe for hatching the brine shrimp eggs was not producing acceptable results with the eggs currently being supplied in the Environments Module. It appeared to be too concentrated. I needed data. It looked like an opportunity for Mrs. Martin's concerned students to help out.

I suggested to the class that the two most critical variables in a hatching investigation were salt concentration and live eggs. I sent a sample of eggs that I was sure were viable and proposed that the class test these eggs and their eggs in a series of salt concentrations. I also let them know that I was anxious to see their lab report.

Data table

On December 15, I got the report. The students had designed and conducted a nice experiment. They set up two identical sets of cups with 100 ml of water and from 0–7 ml of kosher salt. In one set they put a tiny spoonful of the questionable eggs from their kit, and in the other set they put a tiny spoonful of the eggs I provided. Here is their data table.

Sure enough, they determined that the original eggs in the kit were no longer viable. And, after two days, the new eggs had hatched in all of the salt concentrations they had tested, except for 0 ml of salt. Included with their report was a sample of the eggs they had determined to be dead. In the spirit of good science, I replicated their experiment, following their procedure precisely. After three days I was able to confirm their results and conclusions.

The students at Adams Elementary experienced some difficulty determining which salt concentrations provided the optimum environment for hatching. My results suggested that the lowest salt concentrations provided the greatest hatching and that hatching actually declined in the more concentrated salt solutions. This will require a revision of the student sheet in the Environments Module.

Thanks go out to Mrs. Martin and her class of excellent scientists. Their pursuit of answers to questions about the natural world represents science at its highest level. As a result of their good work, we have two important bits of information to share with teachers around the country using the Environments Module.

  1. Test those brine shrimp eggs a week or so before you plan to teach Investigation 5. Dissolve a 5-ml spoon of kosher salt in 150 ml of water. Add one minispoon of your brine shrimp eggs. In two days you should have a little swarm of pinpoint-sized hatchlings moving around in the cup.
  2. Modify the brine shrimp hatching experiment procedure and student sheet no. 17, Hatching Brine Shrimp, by reducing the amount of salt in half. You should still use the 5-ml spoon and 150 ml of water, but use only half as many spoons of salt. The cups will then be labeled 0 spoons, 1 spoon, 2 spoons, and 3 spoons. Student sheet no. 17 should be modified in a similar fashion.