Tank Tips: A Freshwater Aquarium in the Classroom

Originally appears in the Spring 2006 issue

Some of my favorite high school memories are of sitting in science class watching fish in the many aquariums that lined the room. The counters bordering the classroom held about 20 aquarium tanks of different sizes, representing various freshwater habitats from all over the world. These aquatic communities included pink kissing gouramis, Mexican blind cave fish, a community tank of tetras, a three-foot-long African lungfish (who was hand fed red worms once a day), and platties and swordtails who gave birth to endless schools of tiny fry. We watched the way the fish communities interacted and changed as new fish were added or babies were born. We helped change the water, maintain filters, feed the fish, and design the “landscape” inside the tanks. The science classroom was always an interesting place to be, and the lessons I learned went far beyond science curriculum. I gained a very practical understanding of the effects of water quality and chemistry, developed a sense of ownership and responsibility towards the care of our classroom, and gained skills that have enabled me to enjoy a lifelong hobby of keeping tropical freshwater fish.

Today, I still keep tropical fish, both at home and at school, and enjoy sharing a classroom aquarium with my students. Teachers who are interested in adding a freshwater aquarium to their classroom will find that it offers both aesthetic appeal and the opportunity to integrate learning across many disciplines. Students may study chemistry as they learn how to test water quality, biology as they learn about the anatomy of a fish, math as they calculate how many fish can live in tanks of different sizes, and geography as they map the places in the world where their tropical fish came from. In addition to benefiting academically, students have the opportunity to learn and practice responsible behavior by helping to care for the fish and maintain the aquarium. Further, observations of the interactions of the fish provide excellent opportunities to discuss social relationships and classroom dynamics.

The following tips are intended to help teachers select aquarium equipment and freshwater tropical fish that are suitable for the classroom, and to link the classroom aquarium to various subject areas of the curriculum.

Selecting a tank

Aquarium tanks are available in many sizes and shapes, and range from the simple and low-cost to the very elaborate. The standard small tank holds 10 gallons (38 liters), but a slightly larger tank is easier to maintain because water chemistry will not fluctuate as rapidly in a larger volume of water. A 20- to 30-gallon (75- to 115-liter) tank is usually a good size for a classroom. Be sure to select a sturdy table or stand on which to place the tank and to position it near an electrical outlet and away from direct sunlight, heaters, and air conditioners.

Every tank needs a lid to keep out dust and a light for easy viewing of the fish. If you are not adding live plants, the standard fluorescent lights supplied with most aquarium hoods will be sufficient for viewing your fish. The light should be set on a timer and turned on no more than 12 hours per day, in order to mimic the natural light cycle. If you want to include live aquatic plants in the tank, you will need to purchase a much higher quality light than is typically sold at pet shops.

Filters, heaters, and air pumps

All tropical tanks need a heater and filter, and a wide variety of these are available on the market. A filter helps to keep the tank clean, aerate the water, and maintain proper water chemistry. Most filters utilize several filtration methods: mechanical filtration, which removes solids such as dead plants and solid fish waste; chemical filtration, in which activated carbon or another medium removes organic pollutants chemically; and biological filtration, in which beneficial bacteria break down ammonia and nitrite into less harmful substances. The three most common types of filters are those that are submersed entirely in the tank, filters that hang on the back of the tank, and canister filters that are usually housed in a cabinet under the tank. By far the simplest and most user-friendly for children and beginner hobbyists is the hang-on variety, as it is mechanically simple, is easy to access for cleaning, and does not require complicated tubing and plumbing. A hang-on filter also provides adequate aeration (eliminating the need for an air pump), provided that it is large enough for the tank and is properly maintained.

An aquarium heater is necessary in order to maintain the water temperature in the range that most tropical fish prefer, between 76 and 80 F (24.5 to 26.5 C). A fully submersible heater, rather than the kind that clips onto the top edge of the tank, is preferable, as the non-submersible variety will break if it is accidentally dropped into the tank.

Air pumps and air stones add pretty bubbles but are more decorative than functional. Although air pumps can help to add oxygen to the water, I would not recommend their use in a classroom as they tend to be noisy. However, if your filter is not the hang-on variety, it may not provide adequate surface turbulence to aerate the water and you may need an air pump.

Aquarium decorations

Designing the “aquascape” in the tank is a fun part of setting up your classroom aquarium and a great opportunity for students to learn about the habitat needs and preferences of different fish. Generally, fish need places to hide and several objects or structures in the tank that help them divide the space into homes and territories. Fish placed in a brightly lit, mostly empty tank are more prone to stress and disease than fish living in a tank with plenty of structures and hiding places. A favorable habitat also promotes more natural behavior, and hence provides opportunities for students to observe natural interactions in the aquarium community.

Caves, rocks, plastic plants, and driftwood are all good aquarium additions. Aquatic plants, too, are beautiful and beneficial additions to an aquarium, but be sure to check the specific care requirements of any plants you are considering. Two hardy, beginner-friendly live aquatic plants that will tolerate low light are Java moss (Vesicularia dubyana) and Java fern (Microsorium pteropus). Both of these plants do well when they are anchored to a piece of driftwood (tie them on with fishing line). Be sure that all aquarium additions are non-toxic and insoluble. Many types of rocks, corals, and seashells are not appropriate for freshwater aquariums because they slowly dissolve, releasing minerals that negatively affect the water chemistry. Granite, slate, and sandstone are generally safe for aquarium use.

Aquarium decorations can be anchored in the substrate, which may be gravel or sand, one to two inches (two to five centimeters) deep. Avoid painted substrates, as the paint often flakes off over time; and avoid very large diameter gravel, as fish can become trapped in the spaces between the gravel pieces. If using sand as a substrate, purchase it from an aquarium shop and ensure that is intended for freshwater use (many shops sell sand for saltwater tanks that contains salts and minerals that will negatively affect water chemistry in a freshwater tank). Sand from a beach is not suitable since it will contain too much salt and organic material.

Choosing fish

There are many species of freshwater tropical fish, and many color and form varieties within each species. The best choices for a classroom aquarium are peaceful community fish such as those in the tetra, gourami, danio, livebearer, and rasbora groups. The needs of most peaceful community fish are similar enough that several species can live together. On the other hand, semi-aggressive or aggressive freshwater fish are more challenging to keep and greatly limit the diversity of species that can be kept in the same tank. (The websites listed at the end of this article provide in-depth information on the requirements of various species, including preferred lighting, water chemistry, and recommended tank mates.)

Including students in the selection of fish will encourage them to take an active interest in your classroom aquarium. Students can research behavior, adult size, habitat needs, and other information about various species of fish. As there are hundreds of varieties, a good starting point is to make a list of the peaceful community fish that are available at your local pet shop. If you would like a larger selection of fish than is available locally, consider ordering through an on-line company, or ask your pet shop if they will make a special order for you. Be sure to purchase some livebearers (which give birth to live fry rather than laying eggs) if you want your students to watch generations of fish grow up in the tank (note that some fry will be eaten by larger fish if they are not removed and raised separately).

The number and size of the fish that you can accommodate is determined by the size of your tank. A typical aquarium can support one inch of fish per gallon of water (1 cm of fish per 1.5 liters). For example, a 20-gallon tank may contain only 17 gallons of water due to water displacement by gravel and decorations. These 17 gallons could support four 2-inch fish and three 3-inch fish, or any other combination that adds up to 17 inches of fish. Overstocking aquariums is a common cause of fish death, as it can lead to rapid fluctuations in water chemistry and result in dissolved oxygen levels that are too low for many types of fish.

Teachers will also want to consider the origin of their fish and the environmental implications of keeping exotic fish in the classroom. While it is possible to keep some varieties of native fish in the classroom, it is usually necessary to obtain them from the wild as they are not commonly available commercially. In addition, many species of native fish will grow far too large for a typical classroom aquarium and may require cooler, faster running water than it is feasible to provide. In many parts of the world, fish populations are dwindling due to habitat loss, over-fishing, and water contamination, making wild collection of either native or tropical species undesirable. However, more than 800 varieties of freshwater tropical fish are captive bred and tank raised, primarily in the U.S. and Asia. (By contrast, only 10 percent of commercially available saltwater fish are captive bred and raised, the remainder being harvested from increasingly endangered coral reefs and other marine environments.) When purchasing fish, look for dealers who specify the origin of the fish — whether tank-raised or wild-collected, and where they are from.¹ Researching and purchasing tank-raised fish provides an opportunity to talk with students about many environmental and ethical issues, including the distinction between wild and domestic animals and the ethical and environmental implications of the exotic animal trade.

Classroom aquarium challenges

Keeping an aquarium has many rewards, but when deciding to add a tank to your classroom it is also important to consider the challenges. Weekend, holiday, and summer maintenance needs to be planned, as it is very difficult to move an aquarium home for the holidays. During short vacations, a timer and automatic feeder can be used to turn aquarium lights on and off and to feed the fish, but the tank should be checked every five days or so to make sure the equipment is working properly. Aside from vacation care, normal tank maintenance includes changing 20 percent of the water every two weeks, monitoring water chemistry through regular water testing, and basic care and cleaning of aquarium equipment (filter, glass, etc.). Testing and charting water chemistry and performing routine maintenance on the tank are good opportunities to involve students in the care of the aquarium.

Fish death is a challenge that most teachers will face at some point, and is not uncommon in the first few weeks when water chemistry is stabilizing in the tank. The manner in which death is handled by the teacher and students will depend on the age of the children. I believe it is best to establish with students from the start that, together, you will do your best to provide a good, healthy home and care for your fish responsibly, but that sometimes fish die and you will talk about it further if it happens. Fish death, although unfortunate, can provide opportunities for discussing feelings and life experiences, and how we learn and grow from those experiences.

Curriculum links

Once it is set up, a classroom aquarium can be integrated into many areas of the curriculum. Following are lesson and activity ideas for several subjects.

English literature: Read children’s stories about fish and have students write their own stories based on observations of the classroom aquarium. Clara and Asha, a story by Eric Rohmann about a little girl with an imaginary fish friend, will inspire students to think creatively about fish beyond the aquarium. Swimmy, by Leo Lionni, provides opportunity to discuss diversity, problem solving, and the value of teamwork. Fish is Fish, also by Leo Lionni, is the humorous story of a tadpole and a minnow who are born at the same time and look very much alike, but are surprised when they grow up to be different creatures with very different life experiences. What’s It Like to Be a Fish? by Wendy Pfeffer is an excellent introduction to fish biology and life cycles for younger children.

Math: Many mathematical calculations are involved in setting up and maintaining a classroom aquarium. For example, students can calculate how many fish can live in tanks of various sizes, calculate the volume and surface area of the aquarium, learn to read water temperature on a thermometer, and graph changes in water chemistry over time.

Science: Students may learn basic biology concepts through studying, labeling, and drawing fish anatomy, and learn about habitats and ecosystems through researching and creating aquarium habitats similar to the native environments of particular fish. They may study fish adaptations by observing different mouth forms and feeding habits, and by considering how body shape and color may have been influenced by a fish’s natural environment. As part of routine maintenance of the tank, students may test and chart water chemistry parameters and experiment with different types of filter media.

Many natural webs and cycles occur in a well-balanced aquarium, and these too may be studied, drawn, and observed. For example, an aquarium with live plants will have a simple food chain, with plants as the primary producers, snails or herbivorous fish as primary consumers, and beneficial bacteria serving as decomposers. Aquariums with live plants also serve to demonstrate photosynthesis. A very important cycle in tanks with or without live plants is the nitrogen cycle, a process by which toxins such as ammonia and nitrites (from fish waste and decaying plants) are converted by beneficial bacteria into less toxic nitrates. Plants and animals use the converted nitrogen to grow, thereby completing the cycle. The levels of ammonia, nitrite, and nitrate in the aquarium can be easily tested, making it possible to chart the progress of the nitrogen cycle in the aquarium.

Social Studies/Geography: Mapping the countries of origin of various tropical species is an excellent way to explore world geography. Various cultures may be highlighted by studying the history of fish keeping around the world (Japanese koi are a particularly good example).

Social Skills: Students can develop responsibility and ownership through participating in the care of a classroom aquarium. Additionally, observing fish behavior provides opportunity to talk about bullying, community, cooperation, and other classroom dynamics that are reflected in the aquarium community.

Finally, a classroom aquarium can be used as a link to studies of the native fish in your area. Enjoyment of tropical fish in the classroom often sparks students’ interest in learning where fish live in their local community, what their habitat is like, and how human activities might affect them. My hope in sharing a classroom aquarium with my students is to teach responsible behavior towards and respect for living things, to provide interdisciplinary curricular connections, and to inspire curiosity about the fish that are native to our community.

Note

¹ Live Aquaria, <www.liveaquaria.com>, sells many captive bred and tank raised tropical fish and provides information about the origin of the fish they sell.

Web resources

The Krib, <www.thekrib.com>. This website and community devoted to tropical fish keeping is an excellent source of step-by-step instructions for setting up an aquarium and in-depth profiles of many fish species.

Tetra Fish <www.tetra-fish.com/aquademics/>. This website provides instruction on setting up and maintaining an aquarium, and has a section for teachers that includes lesson plan suggestions, printable activity sheets, and on-line games for students.

[/content_protector]

To view the photo-rich magazine version, click here.

If you are not already a subscriber, please subscribe to read the full article 

Rebecca Holcombe is an environmental educator and the Director of Community Programs for Common Ground High School and the New Haven Ecology Project in New Haven, Connecticut.