Branchinecta mackini, commonly known as The Alkali Pool Fairy Shrimp, belongs to the Branchinectidae family. This species can be found in a diverse range of habitats, including dry lake playas, predominantly during the cooler seasons of the year. Although often associated with alkaline habitats, Branchinecta mackini is not limited solely to these environments. It can be frequently observed in Canada, Mexico, and the United States, states such as California and Nevada.
Anatomy: The characteristics outlined below may exhibit variations influenced by environmental conditions, population dynamics, and the organism's age.
Head:
Second Antenna:
The shrimp has a second antenna that is close to the body (proximal antennomere) with a back-middle outgrowth (basal posteriomedial apophysis) and small spines spaced along its middle side. The far end (distal antennomere) of the second antenna curves towards the middle, with a major bend located in the middle near part. This part is somewhat flat, with a tip that does not curve backward.
Female: Have reduced second antennae and the first antenna is longer than the second antenna.
Thorax:
Dorsolateral Process:
Male: Absent.
Female: The upper side of the thorax (the part of the body between the head and the abdomen) does not have lobes.
Thoracopods:
Male: Limbs are more curved in shape containing more spines than fine setae.
Female: Limbs are more rounded with fine setae.
Reproductive Segments:
Male: A pair of penes.
Female: The ovaries have two branches (biramous) with the lateral egg duct positioned at the beginning of the second genital segment. The groove for mating (amplexial groove) is not differentiated, and the pouch for carrying eggs (brood pouch) is cylindrical with no structures to receive the male’s second antennae during mating. The tip of the pouch ends under the second or third abdominal segment (fourth or fifth segments without legs).
Cyst:
The egg is round, with tiny, raised lines (cortical crests).
Abdomen:
No unique features and consistent between sexes.
Tail:
Cercopods:
The tail appendages (cercopods) do not converge and are set with feathery bristles (plumose setae) along the middle and side borders.
Morphology:
Size: 2 cm to 2.5 cm in length, contingent on prevailing environmental conditions.
Coloration: The body is mainly transparent but can have undertones of browns, tans, and blues.
Captivity and Growth:
Growth is influenced by multiple factors such as temperature, salinity, and care. These temperature ranges are based on our experience but do not represent the maximum or minimum.
Hatching Temperature Range: 50 to 72°F.
Temperature Range for Adults: 50 to 75°F.
Hatching: At temperatures of 60 to 72 Fahrenheit, nauplii appeared after 24 to 48 hours.
Growth Rate: This species has a moderate growth rate, achieving sexual maturity within 10 to 14 days. The average lifespan spans 8 to 10 weeks.
Behavior: This fairy shrimp is a moderately slow-moving species, swimming gracefully throughout the water column, feeding on microorganisms. If no food is readily available, they will scrape substrate from the habitat floor to feed on. They tend to stay near the bottom of the habitat, barely floating over the substrate most of the time. They constantly swim in a forward motion; however, females can swim stationary for a bit more often.
Reproduction: Males utilize their second antennae to swiftly latch onto females during mating, a process lasting only a few seconds.
References:
Obregón-Barboza, Hortencia, et al. "A Review of the Branchinecta (Branchiopoda: Anostraca) from the Baja California Peninsula: First Record of the Giant Fairy Shrimp B. gigas Lynch, 1937 from Mexico." Journal of Crustacean Biology, vol. 35, no. 3, 2015, pp. 433-440.