U.S. Fish & Wildlife Service

Sacramento Fish & Wildlife OfficeServing the people, conserving the fish, wildlife, and plants of California

A Unit Of The Pacific Southwest Region

Species Information

Longhorn Fairy Shrimp

Branchinecta longiantenna

Basic Species Information


Endangered. This species is in danger of extinction throughout all or a significant portion of its range.


The longhorn fairy shrimp is a small crustacean in the Branchinectidae family. It ranges in size from 1.3 to 2 cm (0.5 to 0.8 inch) long. Fairy shrimp are aquatic species in the order Anostraca. They have delicate elongate bodies, large stalked compound eyes, no carapaces, and 11 pairs of swimming legs. They glide gracefully upside down, swimming by beating their legs in a complex, wavelike movement that passes from front to back.


The shrimp feed on algae, bacteria, protozoa, rotifers and bits of detritus.


Longhorn fairy shrimp inhabit clear to rather turbid vernal pools. These include clear-water depressions in sandstone outcroppings near Tracy, grass-bottomed pools in Merced County and claypan pools around Soda Lake in San Luis Obispo County. Longhorn fairy shrimp have been collected from late December to late April.


Female fairy shrimp carry their eggs in a ventral brood sac. The eggs either are dropped to the pool bottom or remain in the brood sac until the mother dies and sinks. When the pool dries out, so do the eggs. They remain in the dry pool bed until rains and other environmental stimuli hatch them.

Resting fairy shrimp eggs are known as cysts. They are capable of withstanding heat, cold and prolonged desiccation. When the pools refill, some, but not all, of the cysts may hatch. The cyst bank in the soil may contain cysts from several years of breeding.

Hatching can begin within the same week that a pool starts to fill. Average time to maturity is 43 days.


The four known populations of longhorn fairy shrimp include:

  1. areas within and adjacent to Carrizo Plain National Monument, San Luis Obispo County
  2. areas within the San Luis National Wildlife Refuge Complex, Merced County
  3. areas within the Brushy Peak Preserve, Alameda County
  4. areas within the Vasco Caves Preserve, near the town of Byron in Contra Costa County


Habitat loss and fragmentation is the largest threat to the survival and recovery of vernal pool species. Habitat loss generally is a result of urbanization, agricultural conversion, and mining.

Habitat loss also occurs in the form of habitat alteration and degradation as a result of changes to natural hydrology, invasive species, incompatible grazing regimes, including insufficient grazing for prolonged periods; infrastructure projects (e.g., roads, water storage and conveyance, utilities) and recreational activities (e.g., off-highway vehicles and hiking), erosion, climatic and environmental change and contamination.


Just about any place you live, you can help restore streams and ponds. Search the Internet for words like volunteer, stream, river, watershed, restoration, clean-up, and the name of your town or area.

See What You Can Do to Help Wildlife and Plants (201 KB | PDF) for ideas about how to help threatened and endangered species.

Last updated: December 1, 2017