Environments
Plant and Animal Care

Students investigate the following animals in the Environments Module

Pillbugs and Sow Bugs
Beetles (Tenebrio)
Goldfish
Aquatic Snails
Amphipods
Elodea
Lemna (Duckweed)
Brine Shrimp

Click on any animal to find out specific information about its care.

Introduction to Life in the Classroom

In several of the FOSS modules and courses, living organisms are brought into the classroom to be cared for and observed by K-5 students. Through the direct experience with organisms provided by these modules, we hope to engender in students a sense of respect for all life and to spark a desire to understand the complex systems that support life on Earth.

The FOSS program endorses the National Science Teachers Association Guidelines for Responsible Use of Animals in the Classroom as they apply to elementary and middle school classrooms.

The FOSS program provides detailed information on how to obtain organisms, how to prepare for their arrival, how to care for them in the classroom, and how to instruct students to properly handle each animal. The animals in the modules were selected because they are abundant, safe for students, easy to care for, and hardy and well-adapted to classroom environments. FOSS selected organisms that were nonexotic, commonly available from local and regional suppliers, and, in some cases, found in the natural environments in many regions. When investigations are carried out as described in the FOSS teacher guide, the insects, worms, crustaceans, snails, and fish are not harmed in any way.

To read more about the FOSS/Delta Policy Statement on Living Organisms in the Classroom, please click here.

PILL BUGS AND SOW BUGS

Iso is Greek for "similar or equal." Pod means "foot." Put them together and you have the isopod, an organism that has an equal number of feet or legs on both sides with all legs similar to one another. Isopods have 14 legs that all function the same. This distinguishes them from closely related organisms that have legs that are modified to perform different functions, such as walking, feeding, feeling, grasping, and so on.

The many different species of isopods around the world share certain characteristics. Isopods are crustaceans, distant kin of shrimps, crabs, and crayfish. Like all crustaceans, isopods have a segmented outer shell (seven overlapping plates) that provides a measure of protection from the environment and predators. Like their aquatic relatives, isopods get the oxygen they need to survive through gill-like structures located at the bases of their legs, rather than through lungs like most terrestrial organisms. That is why isopods must keep moist at all times—if they dry, they die.

Two kinds of isopods are of interest as classroom organisms. The genus Armadillidium (arm•uh•duh•LID•e•um) is known casually as the pill bug or roly-poly. It gets these names from its habit of rolling into a tight sphere when threatened or stressed. The pill bug has a highly domed shape, short legs, and inconspicuous antennae. When in its defensive rolled posture, it is hard for a predator to grip, and it is also more resistant to drying out.

Pill bugs move slowly and have a difficult time righting themselves if they roll onto their backs on a smooth surface. They range from light brown to dark gray or black. Often they have white, cream, or yellowish spots on their backs. The largest individuals of this kind of isopod can be 1 cm long, but most are 7 or 8 mm.

The second isopod used extensively in classrooms, genus Porcellio (por•sel•E•oh), is commonly called the sow bug or wood louse. These names are potentially confusing because Porcellio don't show a particular affinity for swine, nor are they lice. They are relatively flat with legs that extend a little bit beyond the edge of the shell, and they have powerful antennae to sense their environment. They move rather quickly and will use their long antennae and little spikelike tail projections to right themselves if they happen to roll onto their backs. Sow bugs come in a surprising array of colors, including tan, orange, purple, and blue, as well as the usual battleship gray. Their size is similar to that of the pill bug.

In the wild, isopods are not usually seen out and about. They are members of that large category of animals known descriptively (not taxonomically) as cryptozoa, or hidden animals. They are most often found in layers of duff and leaf litter, under rocks or logs, or burrowed a short distance under the surface of the soil. The environment they seek is moist and dark, in or near dead and decomposing wood and other plant material. The former is their main source of food, accounting, perhaps, for their common name of wood lice. Isopods are not, however, above eating fresh strawberries and carrots, making them a minor pest in the garden.

Life cycle. There are both male and female isopods, but only another isopod can reliably tell them apart. After mating, the female lays several dozen eggs, which she carries in a compact white package on her underside between her legs. This package is a specialized brood pouch, the marsupium, in which the eggs develop for 3 or 4 weeks before hatching. A few days after hatching, a swarm of fully formed, minute isopods strike out into the world. They are nearly invisible at first but soon grow to a size that can be seen by the unaided eye. Like all crustaceans that carry a hard outer shell, isopods must shed their shells in order to grow. In the molting process the shell is cast off, and the new soft shell underneath expands before hardening. Interestingly, the whole shell is not shed at once; first the rear (posterior) shell segments are shed, and 2 or 3 days later the front (anterior) ones fall off.

What to do when they arrive. The shipping container contains damp paper to provide moisture. Upon arrival, mist paper slightly. Food should be removed if it shows any sign of mold and replaced with sliced carrot, potato, or apple. Pill bugs and sow bugs can be kept in the shipping container for a few days until ready to use in class. Moisten the paper towels as necessary.

If you are keeping them for a longer period of time, place them in a terrarium with rich, moist soil. Place moist paper towels in the container to provide humidity. Continue to add vegetables, replacing them as necessary to control mold. Keep container at room temperature in low light.

Classroom habitat. Isopods are excellent classroom animals—they exhibit interesting behaviors, they are small but not tiny, they don’t bite, smell, fly, or jump, and they are easy to care for. Isopods can live in just about any vessel, from a recycled margarine tub to a 50-liter aquarium. If the container is smooth-sided, it doesn’t even have to be covered, because isopods can’t climb smooth surfaces at all. A layer of soil covered with some dead leaves, twigs, and bark is great, but isopods will be comfortable with some paper towels or newspaper laid on the soil. They do like to have some structure to crawl under.

Food and water. The most important thing to remember is that the soil must be kept moist at all times—not wet, but moist—so that the isopods don’t dry out. A chunk of raw potato in the container with the isopods serves as a source of both food and moisture. Otherwise they will eat the decomposing leaves and twigs or the paper towels and newspaper.

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MEALWORMS AND DARKLING BEETLES (Tenebrio beetle)

The mealworm is not a worm; it is a larva. Any similarity to a true worm is incidental. mealworm larvae are golden yellow and have 13 segments—a head, three thoracic segments, and nine abdominal segments Mealworm larvae are the counterpart of the familiar caterpillar in the butterfly story. They pull themselves around on six stubby legs, one pair on each thoracic segment.

Mealworms are the larval stage of darkling (aka Tenebrio) beetles. Beetles, along with all their other insect kin (true bugs, flies, bees, wasps, ants, on and on), are members of the phylum Arthropoda, a word meaning jointed legs. Like all members of their phylum, insects wear their skeleton on the outside like a suit of armor. This is practical when they are under attack, but very inconvenient when they are trying to grow. Arthropods solved this problem by molting (shedding) this outer shell-like cuticle periodically. Immediately following the molt, the soft white larva expands before the new larger cuticle hardens. For mealworms this process repeats five times over a 2-month period, after which the larva is about 3 cm long. The final larval molt reveals the next stage, the pupa.

Life cycle. Darkling beetles follow a life history known as complete metamorphosis. Like butterflies and moths, they go through four distinct stages during their life cycle. A female beetle lays eggs, as many as 500 in her brief lifetime of a month or two. The eggs are about the size of the period at the end of this sentence. After a couple of weeks the equally tiny larvae emerge from the eggs. The larvae are known as mealworms, but of course they are not true worms. The larvae are golden yellow and have 12 body segments. They are the counterpart of the familiar caterpillar in the butterfly story. Mealworms pull themselves around on six stubby legs that are all crowded at the front.

The larvae seem to have two purposes in life: eat and grow. Beetles are arthropods, and like all members of their phylum they wear their skeleton on the outside like a suit of armor. This is very practical when they are being attacked, but very inconvenient when they are trying to grow. The arthropods have solved this problem by shedding (molting) their shell periodically. Immediately following the molt the soft, white larvae expand before the new larger shell hardens. This process may repeat half a dozen or more times over a 3-month period, after which time the larvae are about 2 cm (3/4") long. The final larval molt reveals the next stage, the pupa.

The pupae don't eat and they don't move except for a twitch or two when disturbed. Inside, however, the mealworm is turning into a beetle, much the same as a caterpillar turns into a butterfly while sequestered inside the chrysalis. In 2 or 3 weeks the pupa splits open and out walks a beetle, white at first, but soon turning to brown and finally black after a day. The beetles mate and lay eggs, and the cycle repeats.

Habitat and food. Mealworms and darkling beetles are rarely seen in the wild, but when they are, it is likely to be in a field where wild grasses flourish and seeds are plentiful. They are most often found in barns, grain storage facilities, and food preparation areas. This organism has benefited by living close to human enterprises, because we unwittingly provide a much better environment for the success of mealworms than could be found in the natural world. For this reason mealworms have become a minor pest in grain storage areas.

Mealworms and darkling beetles are excellent classroom animals—they exhibit interesting behaviors, they are small but not tiny, they don't bite, smell, fly, or jump, and they are extremely easy to care for. Mealworms live right in a container of their food source: bran, cornmeal, rolled oats, breakfast flakes, or chick starter mash. All are excellent foods, but bran and chick starter are recommended. The food must be kept dry. Mealworms can go through their complete life cycle without any added water (they are very efficient at extracting water from the food), but it is recommended that small bits of apple, potato, or carrot be added from time to time.

Mealworms should be kept in large, relatively flat containers. They seem to thrive best when the colony has a large surface area. Keep the bran about 2 or 3 cm (±1") deep in a basin, bus tray, aquarium, or plastic shoe box. If the container sides are steep and smooth, it is not necessary to keep the container covered. Adults and larvae seem to prefer hiding under bits of paper or light cardboard; the pupae give no indication that they care.

The mealworm's preferred environment is very dry, moderately warm, and dark. A bit of apple provides extra moisture for the mealworms and seems to stimulate rapid growth. As the temperature increases, so does the rate at which mealworms advance through their life cycle. Under ideal conditions, in a classroom, the complete life cycle can take place in as little as 3 months, but more likely it will take 4 months. Cold slows the process almost to the point of suspended animation. Mealworms can be put into the refrigerator (not the freezer) for periods of time to stop metamorphosis.

In addition to providing reliable opportunities for observing a complete life cycle in the classroom as in the Insects and Plants Module, mealworms can also be used for other activities. In the Environments Module their response to various environmental factors is investigated. Mealworms can be used for structure/function observations and behavior investigations. And they are just nice to have around to remind us that life on earth takes a seemingly endless variety of forms, and that part of being human is to have compassion and respect for all life.

Food and Water. The mealworm culture must be kept dry. Mealworms can go through their complete life cycle without any added water (they are very efficient at extracting water from their food), but it is recommended that moisture continually be provided in the form of small bits of apple, sweet potato, or carrot. Otherwise the larvae and adults may attack each other in search of additional moisture. If carrot or sweet potato is used as the moisture source, the frass will be orange, adding evidence that the granules are waste rather than eggs.

Mealworm Homes. Large cultures of mealworms (200 or more) should be kept in large, relatively flat containers. They seem to thrive best when the colony has a large surface area. Keep the bran 5–10 cm (2–4") deep in the clear plastic basin provided in the kit. If you want to expand your mealworm activities, any basin, bus tray, or old aquarium will do. If the container sides are steep and smooth, it is not necessary to cover the container.

The mealworms's preferred environment is very dry, moderately warm, and dark. As the temperature increases, so does the rate at which mealworms advance through their life cycle. Under ideal conditions the complete life cycle can take place in as little as 3 months, but more likely it will take 4. However, students should be able to see their mealworms advance through the three important stages of larva, pupa, and adult in 4 to 6 weeks if the larvae are large and well advanced at the time they are introduced.

Mealworms and darkling beetles are rarely seen in the wild, but when they are, it is likely to be in a field where wild grasses flourish and seeds are plentiful. They are most often found in barns, grain storage facilities, and food preparation areas. This organism has benefited by living close to humans, because we unwittingly provide a much better environment for them than can be found in the natural world.

What to do when they arrive. Mealworm beetles are shipped in a container with a "breathing" cap to provide air. They need no special care but should be used as soon as possible, as they have a rather short life span. Keep beetles at normal room temperatures in low light. Store in a cool place at 45 to 65º F out of direct sunlight. At warmer room temperatures, larvae will soon pupate. Cover loosely with a paper towel to provide crawling space. Add slices of potato or carrot for moisture and add a substrate of bran for food. Replace as necessary or if it becomes moldy.

 

Mealworm Life Cycle
Stage
How long?
Food
Moisture
Other information
Egg 7–14 days      
Larva 30–90 days Bran Apple 5 molts occur
Pupa 10–20 days      
Adult 5–10 days Bran Apple Death: 30 days
Egg The cycle continues.

 

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GOLDFISH AND GUPPIES

Plants and animals that live in water make up the majority of biomass. They have so much more space in which to live. Life undoubtedly originated in the water, and many life-forms have never left it. Living in a dense fluid like water provides a lot of support for organisms, and the free-swimming forms have three-dimensional mobility. And, of course, they never have to worry about where their next drink is coming from.

For many of us a goldfish bowl was our introduction to aquatic animals. The beautiful orange fish are hardy and forgiving in terms of their living requirements. They are good classroom animals, requiring a minimum amount of care to keep them in good shape.

Goldfish weren't always gold; their wild kin are dark gray and olive-green. Goldfish are related to carp, so they have a rather unglamorous lifestyle, spending their time foraging in murky water for a variety of foods, including plants, insects, snails, and the eggs of other fish. The lovely colors and sometimes bizarre shapes of goldfish are the products of selective breeding conducted in China and Japan, where they are native.

A bucket, a bowl, a plastic bag, or a two-story-tall glass box can be an aquarium. A few of the millions of plant and animal species make excellent classroom aquarium organisms. But before we look at the organisms, it is important to think about the factors that make up their environment.

Water. Chlorine in regular tap water can be lethal to both goldfish and guppies. There are two ways to dechlorinate water. The first is to age the tap water by letting it sit in an open container for at least 24 hours. Chlorine dissolved in the water escapes into the air. Or add dechlorinating chemicals (included in the kit) to tap water. In some water systems, chloramine, a newer additive, is used in place of chlorine, and it will not leave the water when exposed to air. You must use water conditioners that specifically say they remove chloramine. It might be beneficial to ask at your local pet store or aquarium store just what is recommended in your area to make the water safe for fish. Set aside a pitcher of water to age, so that you will have it ready to maintain the water level of the aquarium. Keep your aquarium covered to reduce evaporation and to keep dust out and fish in.

The water in an aquarium will be fine for extended periods of time. Aged or treated tap water should be added to maintain the proper level, and about once a month half of the water should be removed and fresh water added in order to reduce the concentration of nitrogen-containing chemicals, the excretory products of the animals.

If a fish dies, or if too much food is put into your aquarium, change the water immediately. If you don't, bacteria will proliferate, taking advantage of the bounty of food. The result will be a putrid smell and danger for your fish and other aquarium animals. The bacteria will quickly deplete the oxygen supply in the aquarium, and the animals will suffocate.

Temperature. Unless you get fish that are specifically identified as tropical fish, it will not be necessary to obtain an aquarium heater. For the classroom it is best to stick to temperate-water organisms—they are so much easier to maintain. In fact, it is more important to keep your aquarium from getting too warm. Warm water holds less oxygen in solution, so aquatic organisms are more comfortable in cooler water. Keep your aquarium away from direct sun except for specific purposes.

Aquarium care. Goldfish don't place many demands on the aquarist. They need unpolluted water, but it is not necessary to provide extra oxygen with an air pump. You may experience some mortality when you first introduce new fish into your aquarium, but this is often due to transportation stress. As long as the fish are not crowded, they will be able to get enough oxygen just from what is dissolved at the surface of the water. To avoid crowding, do not exceed one feeder-size (3 cm) goldfish per liter of water for any extended length of time. You should be able to put six to eight guppies in a basin aquarium.

Food. Goldfish will eat a wide variety of foods, but the most convenient is a commercial flake food. This kind of food floats, and the fish will quickly learn to come to the surface to eat. The most important thing about feeding is not to overfeed! Feed your fish once a day as much food as they will consume in 3–5 minutes. Too much food left in the aquarium will foul the water. Fish-feeding cakes—compressed food that disintegrates slowly—are available at pet and aquarium stores if you need to leave the fish unattended for more than 3 days.

Feed the fish when students can observe the feeding behavior. Goldfish like to eat insect larvae, worms, aquatic plants, and snail eggs (all of which they eat in the wild) as well as commercial food. Guppies also eat commercial fish food, as well as finely chopped fish, tubifex worms, earthworms, and Daphnia.

Reproduction. Goldfish are very prolific in nature and in special breeding ponds, but don't expect any offspring in the classroom. They need lots of plants and other cover to propagate successfully. If they did lay eggs in the aquarium, they would doubtless eat all of their own eggs during their incessant foraging for food morsels. Goldfish can grow to be 40 cm (16") long and may live more than 10 years. Be prepared for an extended stay when goldfish move into your room.

Guppies are small fish that bear live young. The feeder-guppy females are larger and usually a uniform beige or silver gray. Their abdomens become quite large when they are gravid (carrying young). The males are smaller and have longer, flowing tails. Males are the ones with spots of multiple colors. Fancy guppies that have been bred for showy colors can be dazzling.

Guppies are quite prolific and will probably give birth during their stay in your classroom. In fact, you may observe the arrival of baby guppies a day or two after the adults are put in their basin aquarium. The stress of transportation may induce a gravid female to release the babies. Adult guppies will eat the young, so you should supply the aquarium with plenty of Elodea in which the babies can hide, or move the adults to a separate tank. Students will enjoy watching the baby guppies grow.

What to do when the fish arrive. Float the unopened bag in aquarium of dechlorinated or spring water for about 15 minutes to equalize the temperature. When temperatures are equal, pour contents of bag through a dip net into another container and transfer fish from net to the aquarium. Discard shipping water. DO NOT USE CHLORINATED TAP WATER!!!

Maintain aquarium at room temperature out of direct sunlight, adding and/or changing water with treated water as necessary to reduce the concentration of nitrogen-containing chemicals naturally occurring in the water.

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AQUATIC SNAILS


Many kinds of aquatic snails make excellent additions to an aquarium. All snails have spiral shells that get bigger toward the opening as the snail grows. The snail secretes new shell around the opening and moves in, abandoning the narrow reaches at the tip of the spiral in which it lived as a youth.

The muscular part of the snail that protrudes from the shell is the foot. Its mouth is on the foot right where a human’s foot has a couple of toes. Because of this interesting structure, snails are called gastropods, which means stomach (gastro) foot (pod). The snail scrapes algae from the surfaces over which it travels. A few snails in your aquarium will graze on the algae that grows on the sides and make it possible to see what’s going on inside.

Snails lay gelatinous globs of nearly transparent eggs. These may be stuck to plant material or the sides of the aquarium. After a couple of weeks, they will hatch, and the tiny larvae will swim freely around the aquarium. Soon they begin to grow a shell, which weighs them down and makes them pedestrian. You may find your aquarium swarming with tiny snails. Snails are quite cooperative about providing opportunities to observe their life cycle.

What to do when they arrive. Immediately upon arrival, open bag and place in cup or similar upright container to prevent tipping. Rinse snails with dechlorinated or spring water prior to transferring to aquarium. Snails will feed on algae or decaying plant matter naturally found in the aquarium.

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Amphipods

Gammarus, also called scuds and side-swimmers, are amphipods. Most amphipods are marine, but there are 50 American species living in fresh water. They live in unpolluted lakes, ponds, streams, brooks, springs, and subterranean waters.

The body of Gammarus is laterally compressed and consists of a cephalothorax (head/thorax), seven free thoracic segments, a six-segmented abdomen, and a small tail (telson). They have seven pairs of thoracic legs, some of which are adapted for swimming and some for walking. This accounts for their Latin name, amphipod: amphi meaning "both," and pod meaning "feet or legs." Their eyes are well developed, and they have two pairs of antennae.

In general, Gammarus are much more active at night than during the day hours. They crawl and walk using their legs in addition to flexing their whole bodies. When Gammarus swim, they often roll over on their side or back (hence the name side-swimmer).

Amphipods usually live close to the bottom or among submerged objects where they can hide from their predators, fish. Their environmental preference is for dark areas. They are scavengers, browsing on microscopic plants, animals, and decomposing material. Unlike brine shrimp, amphipods are not adapted for withstanding drought and other adverse environmental conditions.

Reproduction. Most Gammarus breed between February and October, depending on the water temperature. During mating, the males carry the females on their backs. Paired individuals feed and swim about for up to a week or until the female is ready to molt. The two animals separate for a short while as the female sheds her old shell. The two pair up again, and mating occurs shortly thereafter. The female keeps the fertilized eggs in a brood pouch, or marsupium, where the eggs hatch after 1 to 3 weeks. Young stay in the pouch until their mother molts again, which might be in a week or so.

Care of Gammarus is the same as care of Daphnia.

What to do when they arrive. Upon arrival, transfer into a larger container of dechlorinated or spring water, using a large baster or by pouring contents directly from the shipping jar. Keep container at room temperature out of direct sunlight. Gammarus are scavengers and feed on microscopic algae and protozoans normally found in pond water. If keeping for longer periods of time, introduce aquatic plants into the aquarium which, as they break down, will provide food.

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ELODEA (ANACHARIS)


Plants occupy the base of the food pyramid in aquatic systems just as they do in terrestrial systems. Inconspicuous single-celled algae that turn your aquarium green capture the sun's energy and provide food for countless minute animals in the water. If you want to stimulate an algae bloom (population explosion), put a goldfish in an aquarium, place it where it will get direct sun several hours a day, and provide the fish with plenty of food. When you see the water turn green, it's a sign that your aquatic plants are growing beautifully.

FOSS activities also use vascular aquatic plants. The popular goldfish-bowl plant that looks like a green feather boa is Elodea (or sometimes Anacharis). In nature it is usually rooted to the bottom of a stream or pond, but in your aquarium it can just float around. It is a good food source for amphipods, fish, and crayfish and will contribute to the oxygen in the water as it photosynthesizes. It also provides crannies where small animals can hide from predators.

Care of aquatic plants is easy. Keep plenty of water in their container.

What to do when the plants arrive. Open bag and rinse plants in dechlorinated or spring water. Keep Elodea floating in bowl of dechlorinated or spring water to avoid drying out until it's ready to use.

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DUCKWEED


Lemna, also known as duckweed, is a tiny floating green plant that looks superficially like a bunch of diminutive lily pads. An individual plant never gets any larger than a few millimeters, but they can proliferate to cover huge areas of water completely. Ducks are fond of it and do their part to keep waterways open, along with many other animals that find it a good food source. Lemna is a good plant for population studies because of the rate at which it multiplies by division of the fleshy leaves. Lemna is the smallest of the flowering plants, but it rarely blooms.

Care of aquatic plants is easy. Keep plenty of water in their container.

What to do when the duckweed arrives. Transfer contents of shipping container to small sieve or dip net. Rinse in dechlorinated or spring water. Introduce duckweed to aquarium where it will float and provide food for other organisms.

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BRINE SHRIMP


Brine is a salt solution—usually a saturated salt solution. And we have all seen a shrimp or two, even if only in cocktail sauce. Brine shrimp might therefore sound like some kind of pickled seafood delicacy, but that's not the case. Brine shrimp, also called fairy shrimp and sea monkeys in some contexts, are tiny but important organisms found in salt ponds and saline lakes.

Artemia salina is the scientific name for brine shrimp. Like their distant cousins the lobster and crab, brine shrimp are aquatic crustaceans. Unlike their marine relatives, brine shrimp live only in bodies of salt water that are isolated from the ocean. They are found reliably in the Great Salt Lake in Utah and Mono Lake in California, but they can appear in unlikely temporary salt ponds after a torrential rain in the desert.

Brine shrimp are small unsubstantial-looking creatures of 1 cm (1/2") or so in length. They glide smoothly through the water, propelled by what appear to be two wings along their sides. Viewed under a microscope, the "wings" are revealed to be 11 pairs of appendages that undulate and act as paddles. As brine shrimp glide along, they feed on microscopic organisms suspended in the water: algae, yeast, and bacteria.

There are both male and female brine shrimp. Following mating, the female will develop either live young or eggs in her egg sac. A female's first batch of young are born alive. After that, eggs form and are released into the water. Eggs may hatch soon thereafter, or they may lapse into a dormant state. The eggs are amazing in their ability to completely dry out and maintain their viability. Brine shrimp eggs can lie in the desert for 10 years or more, waiting for the right environment, and then spring into life to start their life cycle again.

Just after hatching, the larval brine shrimp, called a nauplius, is no bigger than the period at the end of this sentence. This is the stage that students will look for as evidence of hatching. They will suddenly see that the tiny dark points in the water are making jerky little movements. The nauplius grows fairly rapidly when conditions are favorable (food, oxygen, and the right concentration of salt), molting its outer shell frequently. It takes 3 to 6 weeks for the shrimp to reach maturity.

A key factor in the environment of brine shrimp is salt. They are adapted for life in a wide range of salt concentrations (as low as 25 parts of salt per 1000 parts of water to as high as 300 parts per 1000), but their optimum salt environment is around 80 parts per 1000. This is more than twice as salty as the ocean, which is about 35 parts of salt per 1000. Brine shrimp are one of the most salt-tolerant animals in the world. Conditions as salty as this result when a body of water has streams running into it, but not out. Salts carried in by natural erosion over countless years raise the salt concentration to the levels preferred by brine shrimp.

What to do when they arrive. We strongly recommend that you test the suitability of your local tap water and the viability of your brine shrimp eggs a week or so before you plan to do the investigation. Put 150 ml of aged tap water in two cups. Add one 5-ml spoon of salt to one cup and label it "1 spoon," and two 5-ml spoons of salt to the other cup and label it "2 spoons." Transfer 1 level minispoon of brine shrimp eggs to each cup. Put the lids on and gently swirl the cups to wet the eggs.

If al goes well, in 24 to 48 hours, at room temperature, you should see the tiny brine shrimp swimming about. You must look closely: Any movement of the water will interfere with your ability to see hatched shrimp, so leave the cup on the table and look into it from the side and down from the top (take the lid off). Eggs float, but larvae swim about.

If no eggs have hatched after 72 hours, purchase bottled spring water and try again. If you still have no success, the viability of the eggs is suspect. Viability is certain for a year or two, so if your eggs are old, replace them. Egss can be purchased from Delta Education (go to Environments) or from tropical fish stores.

Hatching brine shrimp. Brine shrimp are easy to hatch, and with luck you can raise them to maturity and keep a stable population going in your classroom for months. They start life fueled by the energy stored in the eggs, but soon they must feed or perish. After the first week of life, they must move to a large container (plastic or glass—no metal) with a new water supply prepared using this formula:

4 liters of water
250 ml of rock salt
30 ml of Epsom salts
15 ml of baking soda

Food: For food, a pinch of baker's or brewer's yeast once a week should be fine. Mark the water level on the container. As water evaporates, add more tap water—not salt water—to keep the salt concentration the same. Put the container near a window or under a light during the day and watch the brine shrimp grow. Adult brine shrimp can be purchased from a tropical fish store. They are sold as fish food.

In addition to environmental investigations involving salinity, brine shrimp are useful for light investigations; they are light seekers. Brine shrimp can be studied as part of a food chain and can be used to demonstrate life cycle.

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