Aquatic Ecosystems Organism Care
Living organisms, including Elodea, dragonfly nymphs, mosquitofish, blackworms, Daphnia, and pond snails are an essential part of this unit. Careful planning and scheduling is the best way to ensure success and avoid the extra expense and disappointment of a die-off.
Download a complete guide to caring for living organisms, including information on ordering the organisms.
Download the At-A-Glance Organism Care for a quick reference guide
Tips for Success
- Order the organisms 3 weeks before students begin to work with them. This means you should stagger your order; dragonfly nymphs are introduced later in the unit, and should be ordered accordingly.
- Plan to teach the unit when temperatures are above freezing and below 90°F. Organisms cannot be shipped during extreme temperatures.
- Alert the office staff at your school that the organisms should be delivered to your classroom as soon as they arrive.
- Set up your holding tanks with dechlorinated water in advance, so you are ready to receive the organisms as soon as they arrive.
- Put the organisms in their holding tanks as soon as they arrive.
- Alert custodians at your school to the presence of live organisms in your classroom, and ask them to avoid using insecticides and cleaning agents that may be harmful to the organisms.
- Keep the model ponds out of direct sunlight and away from heaters.
- Keep the lids on the model ponds when not in use any dust or stray drops of soap, pain, or other pollutants that may accidentally get into the water.
- Do not overfeed the organisms. It is better to underfeed than overfeed. Don’t worry about feeding them over the weekend, including three-day weekends.
- Make a plan for holidays or vacations longer than several days. This is especially important in severe climates where a school’s heat or air conditioning may be turned off during extended breaks. If this is the case, take the model ponds home during the break.
- Replace about 20% of the water every three weeks with clean, dechlorinated water. This helps maintain water quality.
- Make a plan for what to do with the organisms after you finish the unit. Do not release any organism into your local environment or wild ecosystems. For suggestions, see page C48 of the Care of Living Materials section.
- If you have access to 5-gallon tanks, you can use those as holding tanks.
It is possible to substitute like organisms for some organisms used in this unit. Substitution organisms may be hardier in your area, or more readily available. Some possible substitutions are listed below. For more information on organism substitutions, contact Amplify Customer Service at 800-823-1969 (Option 3).
Rinse the Elodea with dechlorinated water and place a few sprigs directly into each of the holding tanks.
The Elodea (water plants) will do just fine as long as they have enough light to make their own food through the process of photosynthesis.
Local pond snails can often be substituted for the pond snails provided with the kit.
Discard the water in which the snails were shipped and rinse the snails with dechlorinated water before placing a few of them into several holding tanks. Snails give off a lot of waste products, so you may want to clean out the holding tanks if you have the snails in them for more than a couple of days. If you clean out the tanks entirely, save at least 50% of the water to return back to the tanks.
Many species of pond snails are herbivores and will eat the water plants and any algae that starts to grow on the sides of the holding tanks. Many pond snails are also scavengers and can be seen feeding on anything that dies in the tank. The pond snails do not need to be given any extra food.
Pour off the water in which the blackworms were shipped, being careful not to lose any blackworms. Use dechlorinating drops to dechlorinate tap water. Add this dechlorinated water to the bag, swirl a bit, and pour off the water. Add more dechlorinated water and pour the blackworms into a clean two- to four-cup plastic container (such as a cottage cheese container). Add more dechlorinated water until there is just enough to barely cover the blackworms with about one-half inch of water. Place the plastic container with the blackworms in the door of the refrigerator (the warmest part of the refrigerator). Rinse them each day with cold dechlorinated water and then place the blackworms back in the refrigerator. Swirl the water in the container and carefully pour off and discard any blackworms that are grey or white in color. Use a fork to remove a few blackworms to place into each of the model ponds in Session 1.5.
Store the blackworms in the refrigerator, covered with approximately one-half inch of water so they can get oxygen, until they are introduced into the students’ model ponds in Session 1.5. There is no need to feed them while they are in the refrigerator. Blackworms eat tiny bits of waste that falls to the bottom of the aquariums; there is no need to feed them.
Upon arrival, transfer the contents of the shipping jar into one of the small holding tanks filled with dechlorinated water, using a large kitchen baster or by pouring contents directly from the jar. Do not net the Daphnia because they must be kept in water at all times. Keep the holding tank at room temperature and out of direct sunlight.
Daphnia are scavengers that feed on microscopic algae. They will also feed on Elodea as it breaks down. Daphnia do very well in water that contains a high concentration of microscopic algae and looks very green. If the water in the holding tank does not have a lot of algae growing in it to feed the Daphnia, the Daphnia can also be fed bacteria or yeast. To prepare bacteria, mash half of a hard-boiled egg yolk in one liter of water. Let it sit for a couple of days. The cloudy liquid that forms will be full of bacteria. A yeast suspension can be prepared by stirring half a package of dry baker’s yeast into one liter of warm water. To feed the Daphnia in the holding tank, simply remove one-half liter of water from the holding tank and replace it with one-half liter of the bacteria or yeast suspension. (Pour very carefully so as not to pour out the Daphnia. You could pour the water through a net, but be very careful not to crush the Daphnia or keep them out of the water for more than a few seconds.) When the water clears in the holding tank, feed the Daphnia again. Daphnia will be added to the students’ model ponds in Session 1.5 where they will do very well feeding on the algae and bacteria growing there.
We suggest using mosquitofish instead of guppies, minnows, or goldfish because they are hardier, and several lessons in the unit focus on students reading, writing, and discussing mosquitofish. However, mosquitofish are banned in some counties. If you are unable to use mosquitofish, we recommend guppies or white cloudfish as substitutes. Students can compare these fish to what they learn about mosquitofish.
The temperature and water chemistry in the holding tanks, compared to what the mosquitofish are accustomed to in the delivery bag, must first be equalized before adding the fish to the holding tank. Following are steps to equalize the two: 1. Float the unopened bag of mosquitofish in the water in the holding tank for around 20 minutes, until the water in the bag is the same temperature as the water in the holding tank. 2. Open the bag and remove approximately 1 cup of water, add approximately 1 cup of tank water, close the bag with a rubber band, and let it stay in the holding tank for approximately another 10 minutes. 3. Repeat this process one more time in order to equalize the temperature and the water chemistry in the bag. 4. When you have completed this process, carefully remove the mosquitofish from the bag with the fishnet included in the kit and place them into two of the holding tanks. Dispose of the water in the bag to reduce the possibility of contaminating your holding tanks. The mosquitofish are not fussy eaters and will actually eat goldfish flake food, pellet food, and algae. They much prefer live food, but do not feed them blackworms and Daphnia while they are in the holding tanks. The mosquitofish are introduced into the students’ model ponds in Session 1.7. Before Session 1.7, feed the flake fish food to the mosquitofish.
It is not necessary to feed the mosquitofish every day; a small pinch of flake fish food every other day is sufficient. Mosquitofish prefer live food, such as blackworms and Daphnia, but they will eat flake fish food and algae. There are only enough blackworms provided in the kit to place three worms in each of the eight model ponds in Session 1.5. The mosquitofish will be very attracted to the blackworms and will probably eat them very quickly. Continue to feed the mosquitofish flake food and save the Daphnia to feed to the dragonfly nymphs.
Damselfly nymphs can be substituted for dragonfly nymphs.
The dragonfly nymphs will arrive wrapped in moist plant material so they are less likely to injure one another during shipping. As soon as they arrive, remove them from the plant material and place them in your holding tanks. The dragonfly nymphs should be separated into a minimum of three holding tanks, apart from any of the mosquitofish or snails, because they have a tendency to eat one another and other organisms that are present. They also need a lot of oxygen. Make sure they have plenty of hiding places (broken clay pots and floating Elodea) so they do not attack one another. The plant material in which they were shipped can be added to your holding tanks once you have rinsed it with dechlorinated water. Soon after adding the dragonfly nymphs to the holding tanks (after a day or two), you might see a lot of what looks like dead nymphs on the bottom of the holding tanks. They are likely not dead nymphs, but, rather, their molts (or exoskeletons). Dragonfly nymphs need to molt in order to grow larger. Use the fishnet when you are ready to transfer the dragonfly nymphs into students’ individual model ponds.
These larval insects are voracious predators of live food, including blackworms, Daphnia, and other kinds of worms, fish, snails, water insects, tadpoles, and mosquito wigglers. They do not eat dead organisms or flake, frozen, or pellet fish food. Dragonfly nymphs are very likely to attack the mosquitofish in the model ponds, especially if they are not given enough other food to hunt and eat. For this reason, it is important to give the fish a lot of hiding places in the Elodea. It is not necessary to feed the nymphs every day; add no more than five Daphnia each week to each of the eight model ponds to make sure you have enough Daphnia to last through Session 3.10 (week 6). If your Daphnia reproduce in the holding tank, you can add a few more to each model pond. However, keep in mind that the more that dragonfly nymphs get to eat, the faster they will molt and grow. To be sure that the dragonfly nymphs are able to prey on the Daphnia, you may want to remove the mosquitofish for a bit before you add the Daphniaso that the mosquitofish do not eat all the Daphnia before the dragonfly nymphs have a chance. If you like, you could supplement the dragonfly nymphs’ diet with additional blackworms and/or a couple of inexpensive feeder fish from your local aquarium store each week.
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