Fairy Shrimp: What They Are and Whether You Can Keep Them

Scoop a jar of water out of a rain-filled ditch or a spring meadow pool and you might find tiny, see-through creatures swimming on their backs, their legs rippling along the body like a slow wave. Those are fairy shrimp, and despite the name they are not the cherry or ghost shrimp you would drop into a planted tank. They belong to an older, stranger branch of the crustacean family, and most of them live and die in puddles that are gone by summer.

They are close cousins of brine shrimp, a distant relative of the shrimp in your tank, and a poor fit for a normal aquarium. Here is what they are, how they live, and what it really takes to keep them.

A planted aquarium like this is the one place you will not find fairy shrimp. They live in bare, fishless seasonal pools, not stable tanks

Quick Answer

Fairy shrimp (order Anostraca) are small freshwater crustaceans, usually half an inch to an inch and a half long, that live in temporary pools where fish cannot survive. They swim upside down using eleven pairs of leaf-shaped legs that double as gills, and they filter tiny food particles out of the water. Their eggs are tough, dormant cysts that survive months or years of drying and hatch once the pool refills.

They are the freshwater relatives of brine shrimp (Artemia), the saltwater animal sold as fish food and marketed as Sea-Monkeys. You can hatch them from cysts in a kit, but they need cool, clean freshwater, cannot share water with fish or predatory triops, and live only a few weeks. Treat them as a curiosity, not a tankmate for your cherry shrimp.

What Are Fairy Shrimp?

Fairy shrimp make up the order Anostraca, one of the most primitive groups of crustaceans alive. The name "anostraca" means "without a shell," and that is the giveaway. Where your tank shrimp have a hard shield (the carapace) over the front of the body, a fairy shrimp has none. The body is long, soft, and nearly transparent, so you often see the gut and the developing eggs right through the skin.

The US Fish and Wildlife Service and the Pennsylvania Natural Heritage Program describe the same basic animal: two compound eyes on short stalks, two pairs of antennae, and eleven pairs of swimming legs called phyllopods. Those legs do two jobs at once. They paddle the animal along, and because they are flat and leaf-shaped they also work as gills. A fairy shrimp can even dial its oxygen uptake up or down, which lets it survive in warm, stagnant pools that would suffocate most animals.

The upside-down swimming throws people off. A fairy shrimp cruises belly-up, legs toward the sky, beating them in a rolling wave. Males are easy to spot once you know the trick: their second pair of antennae is enlarged into hooked claspers that grip the female during mating. The overall effect is an animal that looks less like a shrimp and more like a feather drifting through the water.

Where Fairy Shrimp Live: Pools Without Fish

The defining fact about fairy shrimp is where they live. They turn up in temporary bodies of freshwater, the kind that fill with winter or spring rain and dry out by early summer. Scientists call the classic habitat a vernal pool, a seasonal wetland that holds water for only a few months. The Encyclopedia of Arkansas and USFWS both make the same point: fairy shrimp are found in water that is too small, too temporary, or too isolated for fish to live in.

That is not a coincidence. A fairy shrimp is slow, soft, and defenseless, so a single hungry sunfish would clear a pool in an afternoon. Breeding only in water that dries up gives them a predator-free nursery, and the price is having to pack a whole generation into the short window the pool is wet. The predators they do face are the ones that also tolerate temporary pools: salamander larvae, diving beetles, and predatory water bugs.

These pools come in every size. USFWS records the vernal pool fairy shrimp in everything from a puddle about three centimeters deep to wetlands many acres across, and the group turns up on every continent, including desert lakebeds and Arctic meltwater. Wherever there is water that comes and goes, some species has usually found a way to use it.

One thing to know before you go collecting: several species are protected. The vernal pool fairy shrimp (Branchinecta lynchi) is threatened under the US Endangered Species Act, the San Diego fairy shrimp is endangered, and Buchanan's fairy shrimp is a protected vulnerable species in New South Wales. If you want to keep fairy shrimp, buy cysts of a common species sold for the purpose rather than scooping them out of a wild pool you cannot identify.

The Life Cycle: Eggs That Wait for Rain

Fairy shrimp solve the puzzle of a pool that dries up with one trick. The "eggs" the females carry are really cysts, dormant embryos wrapped in a thick, drought-proof shell. When the pool dries, the cysts settle into the mud and wait. USFWS notes they can stay viable for several years through hot, dry summers, building up what biologists call an egg bank in the soil. That is why a pool that has looked lifeless for years can suddenly swarm with fairy shrimp after one wet winter.

When rain refills the pool, some of the cysts hatch, but not all at once, which hedges against a pool that fills and dries again too fast. The hatchlings then pass through a series of molting stages, called instars, on the way to adulthood.

How fast that happens depends heavily on temperature, and the sources give different numbers because they measure different species and different stages. USFWS reports that San Diego fairy shrimp hatch and mature within 7 to 14 days of a pool filling, while the vernal pool fairy shrimp averages about 18 days to maturity and closer to 40 days to reproduce. Other accounts say a whole cycle can run in as little as 16 days under ideal warmth. The honest summary is one to six weeks from cyst to breeding adult, with warmth speeding it up.

The adults do not last long. They hatch in late winter or early spring, grow for a week or two, breed for one to three weeks, and the population usually fades by mid-spring as the water warms into the upper 60s Fahrenheit and predators move in. The cyst bank in the mud can outlive them by years. The animal you see is brief; the species is patient.

How Big Do Fairy Shrimp Get?

Most fairy shrimp are small. USFWS puts the vernal pool species between about 0.12 and 1.5 inches long, and a Texas Parks and Wildlife account notes that the 16 Texas species top out around half an inch to one and a quarter inches. Think somewhere between a grain of rice and your thumbnail. A handful of "giant" species break the rule, with that same Texas account citing giants of three to six inches, but those are the exception. From a hobby kit, expect delicate half-inch animals, not monsters.

Fairy Shrimp vs Brine Shrimp vs Triops

This is where most of the confusion lives, because all three get sold in novelty "hatch your own" kits and all three make dormant cysts.

Fairy shrimp and brine shrimp are genuinely close. Both sit in the order Anostraca, so a brine shrimp is basically a saltwater fairy shrimp. Brine shrimp are the genus Artemia, they live in very salty water such as the Great Salt Lake, and they are the animal the trade sells live, frozen, and freeze-dried as fish food. They are also the creature rebranded as Sea-Monkeys, a novelty pet launched in 1957 by Harold von Braunhut. So a Sea-Monkey is a brine shrimp, not a true fairy shrimp.

Triops are a different animal. They belong to the order Notostraca, the tadpole shrimp, and they look like a tiny horseshoe crab with a broad shield over the body. The practical difference is behavior: triops are omnivores that turn predatory as they grow, and keepers warn that they will hunt and eat fairy shrimp once big enough. If a kit sells you both, raise them in separate containers or you end up with just triops.

Can You Keep Fairy Shrimp at Home?

Yes, within limits. Fairy shrimp are sold as cysts, often in triops-and-fairy-shrimp kits, and hatching them is a fun short project, especially for kids. But they are harder to raise in numbers than brine shrimp. One recurring complaint on shrimp and amphibian forums is that fairy shrimp eggs sink while brine shrimp eggs float, which makes brine shrimp far easier to hatch in bulk, and that is a big reason Artemia dominates the fish-food trade.

If you want to try, these broad rules come out of the biology and from lab rearing studies. Fairy shrimp species differ a lot, so the supplier's instructions for your exact cysts beat any general number.

• •Use freshwater, not salt. Unlike brine shrimp, most fairy shrimp hatch best in nearly fresh water. Hatching trials in the Journal of Limnology found several species hatched well only at very low salinity, close to distilled water.
• •Keep it cool. The same studies found good hatching for temperate species in the range of roughly 15 to 27 degrees Celsius (about 59 to 81 Fahrenheit), depending on species. Warmer water speeds growth but can be lethal: in one trial every animal reared at 30 Celsius died before breeding.
• •Feed tiny particles. Fairy shrimp are filter feeders. In culture, green water (a light algae bloom) or a dusting of powdered invertebrate food works; the lab studies used single-celled algae and lipid-enriched yeast.
• •No filter, no fish, no triops. A strong filter sucks these fragile animals in, and any fish or grown triops will eat them. A bare container with gentle or no aeration is the norm.
• •Expect a short run. Even in ideal conditions you get a few weeks of adults. Let the females drop cysts, dry the substrate, and you can rehatch later.

If you want to pick up a kit to try it, search for a fairy shrimp and triops hatching kit rather than a specific brand, since stock changes and the cheaper kits hatch just as well.

How Fairy Shrimp Relate to the Shrimp in Your Tank

Here is the part that surprises aquarium keepers. A fairy shrimp is only distantly related to the shrimp you actually keep. Cherry shrimp, ghost shrimp, amano shrimp, and the rest are decapods, the same order as crabs, lobsters, and crayfish, with a hard carapace, true claws on some legs, and ten walking legs. You can see all of that in our shrimp anatomy guide. A fairy shrimp has none of it: no carapace, no claws, and legs built for filtering rather than walking.

So "shrimp" is doing a lot of work as a common name. It gets stuck on fairy shrimp, brine shrimp, tank shrimp, and even animals that are not shrimp at all, the same naming mess we untangle in our crayfish vs shrimp comparison. For the big picture of where all these animals live in the wild, where shrimp live runs from reef to rice paddy to vernal pool.

The closest thing in the hobby to a fairy shrimp's oddball life is the opae ula, the tiny Hawaiian shrimp that lives in sealed brackish jars for years with almost no care. It is still a decapod, but like a fairy shrimp it comes from strange, fish-free water. Our opae ula shrimp care guide and the broader pet shrimp guide are the right next stops if offbeat shrimp are your thing.

Frequently Asked Questions

◆Are fairy shrimp the same as brine shrimp or Sea-Monkeys?

They are close relatives, not the same animal. Both sit in the order Anostraca, but brine shrimp (Artemia) live in very salty water and fairy shrimp live in freshwater. Sea-Monkeys are brine shrimp that were rebranded as a novelty pet in 1957, so a Sea-Monkey is a brine shrimp, not a true fairy shrimp.

◆Can you keep fairy shrimp in a regular aquarium?

Not really. They need cool, clean freshwater with no fish and no strong filter, and any fish or grown triops will eat them. They also live only a few weeks. A bare hatching container works as a short project, but they are not a tankmate for cherry shrimp or community fish.

◆How long do fairy shrimp live?

The adults live only a few weeks, often one to three weeks of breeding after one or two weeks of growth, and wild populations fade by mid-spring as the water warms. The eggs are the survivors: dormant cysts can sit in dry mud for several years and hatch when the pool refills.

◆Why do fairy shrimp swim upside down?

They swim belly-up because their eleven pairs of leaf-shaped legs work as both paddles and gills. Holding the legs toward the surface and rolling them in a wave is the efficient way to move and pull in oxygen at the same time.

◆Is it legal to collect fairy shrimp from the wild?

It depends on the species and where you are. Several, including the vernal pool fairy shrimp and the San Diego fairy shrimp, are protected under endangered species law, and many wild species are hard to tell apart. The safe route is to buy cysts of a common species sold for hatching rather than collecting from a pool you cannot identify.

The Bottom Line

Fairy shrimp show how strange and tough simple animals can be. They swim upside down, breathe through their legs, pack a whole life into a drying puddle, and leave behind eggs that wait out years of drought. They are cousins of the brine shrimp you feed your fish and only distant relatives of the shrimp in your tank, and they belong in a bare, cool, fishless container rather than a planted aquarium. Hatch a kit if you are curious and let them leave cysts for next time. If you would rather keep an odd shrimp that actually lives a long time, start with our pet shrimp guide instead.