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Crayfish Adventures: A Science Project

Tena Brown, Wengert Elementary School, Las Vegas, Nevada
March 15, 2006 | FOSS in Schools

Top image: The dark spot is the baby crayfish's heart, which could actually be seen beating.

It all started innocently enough. Mrs. H had ordered crayfish for the FOSS Structures of Life Module she was planning for her third-grade class. I was going to use them after her. I had already extended my Structures of Life Module to include raising silkworms and hatching chicks, as well as growing beans hydroponically. But I had not used crayfish before. When Mrs. H was through, I inherited her crayfish.

She had been following the directions in the FOSS teacher guide for the care of these crustaceans, and I received them in the shallow tub with the half pots. She had fed them in a separate container each day, returning them to their big tub and cleaning the feeding container. This seemed like a lot of trouble to me. During my youth, my family would gather 20–40 large crayfish from a river near our home in California, cook them, and enjoy eating them in the same way as large shrimp. I also remembered that we would dive three to four meters into the river to grab the tasty critters. So why couldn’t we keep them in an aquarium? Thus the adventure started.

I set up a ten-gallon tank and placed the crayfish in it. I also remembered that the creatures in the river were scavengers, so I decided to feed them something much less messy than cat food. I switched their diet to shrimp pellets and fish food.
They did very well.

When the next school year started, I took them to my room and added them to the menagerie that I had already. The other third-grade teachers were curious about the set-up. One crayfish had died, so I had four left—one male and three females. We were all happy to have crayfish on hand and not to have to order them.

Then came the big surprise. The females came “in berry”! In other words, they laid eggs, hundreds of them. We set up another tank and separated them into two groups.

Mother and eggs

The mother crayfish carries the eggs under her tail.

We recorded the dates that we first saw the eggs and waited anxiously for them to hatch. The eggs are carried under the mother’s tail, and once the eggs hatch, the babies continue to stay there for several days. They are very small when they hatch and nearly transparent, so we had difficulty telling the baby crayfish from the eggs. It wasn’t long before we had hundreds of tiny crayfish swimming in the tanks and getting sucked into the aquarium filter.

The mortality rate was very high. We occasionally saw them attack each other.
Many just disappeared. We set up more tanks, and soon four of our third-grade
classrooms had at least one tank. Two of us had three tanks with crayfish. Few of
the crayfish grew to more than 4 or 5 cm. Some would grow rapidly and attack the smaller crayfish. We started giving the crayfish away to other schools, rather than set up dozens of tanks.

My class decided to incorporate a growth experiment by separating the babies. Each student kept one baby crayfish on his or her desk in a clear cup, documented its molting, and measured its growth over several weeks.

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Photo of two baby crayfish taken through a digital microscope.

They would feed the crayfish shrimp pellets and clean their water every other day. These babies were only about 4 mm in length when we started. If one died, they recorded that on their index card, got another baby, and started again. Students also made a Kid Pix® slide show with pictures of their baby (taken with an Intel®microscope), its mother, and diagrams of body parts.

Near the beginning of this experiment, the local newspaper published an article about a man in Nevada that had switched from raising cattle to raising freshwater lobsters (Australian crayfish). I shared the article with my class, and they had a lot of questions. We made a list of the questions and sent them with a letter to the lobster farmer. He responded by sending us a brochure about the lobsters and explaining that he fed them fish food and dried peas. We decided to extend our experiment by investigating which food types caused the most growth. What we found surprised us. Although there was little difference in growth between the two groups, there were no deaths with the peas. This caused us to wonder how many deaths were due to food source instead of sibling rivalry. The students learned,and so did the teachers.

Inquiry goes on. We continue to learn from the offspring of those original crayfish. Occasionally, one manages to escape a tank and is found dehydrated down the hall or crawling out from behind a bookcase. We have shared our extra crayfish, as well as our experience in raising them, with other schools. It has truly been a great learning experience for both students and teachers.

For more information about this article, contact Tena Brown at Tbrowntena@aol.com.