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Ideas for Using Triops in the Classroom
Over the years I have had many people ask me how to use Triops in the classroom. Several of these questions are the in FAQ section, but I thought it would be nice to have a specific section for teaching, since it is a subject close to my heart. There are web sites that allow you to purchase Triops kits in bulk, for a decent reduction in cost (as low as $3.50/kit), so doing a larger classroom exercise with a number of students rearing Triops in various treatments or habitats is feasible. The major impediment to doing these types of experiments is the fact that Triops are cannibalistic. Thus, when one tries to rear a number in a single container, there can often be a single winner! This in itself could be something to study, but may not be appropriate for some classroom settings. Idea 1For a "winner takes all" experiment, one can follow who is doing well on the basis of molt characteristics that can allow identifications of specific individuals. The end segment of the tadpole shrimp is called the "telson," and has a number of spines on its dorsal surface. These spines are variable, and can be easily seen with a dissecting microscope (or a magnifying lens) on a molt. The shrimp molt 1-2 times a day when young, and so daily collection of molts can be used to follow the success of various individuals in the tank or aquarium. This will only work for a limited number of individuals (I kept track of 16, but that was difficult). It would be easy, though, to keep track of half a dozen or so and measure their size over time (the carapace length is easily measured on the molts, and is a good measure of total size - this is what we do in our research on clam shrimp). The class could track the size of various individuals, and look to see who "makes it" and who doesn't (the common pattern is for the smaller individuals to "disappear" due to being eaten by their larger brethren!). They could do a plot of size vs. age and note the trajectories over time. Idea 2Triops are very sensitive to density. In my research I used 5, 10, and 16 Triops per 10 gallon aquarium. You might want to try something along those lines to show the students how competition works in "the real world." Students could set up a few containers with differing numbers of Triops and look to see the differences in size over time (using the same measurements of carapace size from molts as suggested above). I have had up to 50 Triops in a single 10-gallon tank, and they were all uniformly stunted in growth. You would need several containers, possibly using the containers that come with the Triops kits, and to hatch several batches of eggs for this experiment. Once the young Triops grew their carapaces (2-3 days), they can be counted and moved into the various containers. I would not suggest putting more than 5 Triops into a 1 liter container. The same amount of food should be supplied per container to maximize competition. Again, students could track growth trajectories as in Idea 1 above and compare those trajectories between food types. Or, they could just compare average size at a given age, as above. Idea 3Triops can eat LOTS of different food items (they are omnivores). Students could decide on several different types of food and compare survival and growth on the various food items. You can purchase a variety of food types for fish in fish stores (e.g., goldfish food, freeze-dried brine shrimp, flake food, etc.) that you could use in such a comparison, but I have seen stories on the Internet for use of meat, cheese, and other food items! The difficult part would be to try to standardize the amount given of each type. I suggest figuring out the amount of food suggested by the manufacturers and try to figure out that weight and standardize on that amount for these other food types. Again, students could track growth trajectories as in Idea 1 above and compare those trajectories between food types. Or, they could just compare average size at a given age, as above. Idea 4Triops are known to attempt to stick their eggs onto various vegetation. I have tried a variety of materials to place in the tank that the shrimp can use to adhere their eggs to. I found that small bits of fiberglass window screen were most useful for this behavior. You could give the students an array of materials (all that could be placed in water and that wouldn't leach harmful chemicals or metals into the water) to test their usefulness for this reproductive behavior. This is a fun experiment because it is fun to watch the shrimp lay eggs, if you can "catch them in the act"! Not all shrimp will do this behavior, nor will any one shrimp ALWAYS lay eggs in this way, so be prepared for some randomness for this project. The students could remove the various materials each day (Triops lays 1-2 batches of eggs per day) and compare which had eggs and which didn't. They could also look at the eggs under a dissecting microscope, if you have any available, and look to see how the eggs are laid down and count how many are in any one batch. Idea 5Behavioral experiments might also be interesting. One could determine the amount of time the Triops spend doing different activities, like digging, swimming, foraging, etc. Also, putting a small amount of dye (like a bit of bromphenol blue) in water in a small container with the Triops (see Figure 6) might be useful for showing the water movement around the Triops's swimming appendages. Finally, the neatest observations one can make on these Triops is to see them molt. They molt while swimming, and go through all kinds of contortions to release their old molt. Unfortunately, you cannot precisely predict when molting will occur, so you just need to be lucky to see one, or have a lot in a bowl, and usually one or more will be molting. They molt about once a day, when they get larger.
Links
The Clam Shrimp Information Page - Information, movies and pictures of Triops' close cousins! Crustacea.net - Information about all known crustacea The Large Branchiopod Bibliography - A list of many large branchiopod original publications from the 1800's to present (exclusive of papers on Artemia)
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