Branchinella

Branchinella australiensis - photo© Neil Armstrong

Fairy shrimps are widespread and form an important component of freshwater ecosystems in temperate and tropical regions. Fairy shrimps are small to moderately large, delicate animals of variable colour, and are among the most primitive of all living Crustacea. They are elongated animals without any sign of a carapace, with clearly defined head, thorax, and abdomen. Males and females differ in form of their second antennae, which in males are longer and adapted to serve as a sexual grasping apparatus. The male second antennae are important from a classificatory viewpoint, and female specimens often cannot be fully identified.

Male fairy shrimp compete intensely for mates. Since mating usually occurs just after the female moults, males often grasp her and are towed around while waiting for her to moult. Some females have a chain of these attached males, including some which have died while awaiting her moult!

Branchinella australiensis - photo© Neil Armstrong

Branchinella occur in all Australian States, but, by and large, each species is rather restricted to a local region. About sixteen species of Branchinella have been described from Australia, and almost all are endemic. Forty percent of these are known from a very limited area or just the type locality in the arid zone. They inhabit fresh or slightly saline water, but as a general rule they live in temporary freshwater habitats that lack fish. Fairy shrimps are active, almost always swimming with the ventral surface uppermost, paddling with the thoracic appendages. They feed mainly on micro-organisms, which are collected along a groove between the bases of the thoracic appendages. These face dorsally as the animals swim ventral surface uppermost. Others scrape food from surfaces with the leg setae, and one species predates on other anostracans.

Branchinella have eggs resistant to desiccation as many of their habitats dry up periodically. It may be that the eggs must obligatorily undergo a period of desiccation in order for further development to take place. The eggs can remain viable in completely dry habitats for years or decades. They hatch as soon as conditions are suitable; the adult shrimps appearing soon after the habitat fills with water. After a few weeks to months, as the habitat starts to dries and the water becomes more saline, they lay dormant eggs that fall to the bottom. The population then disappears and does not re-appear until their habitat dries and then refills. The primary habitat for these aquatic species is thus dry for most of the year.

Fairy Shrimp as Live Food
Fairy shrimp are freshwater relatives of the more popular brine shrimp (Artemia spp.), and offer interesting possibilities as live food for fish larval culture. They are probably more appropriate than Artemia as a live food for freshwater fish. Their high carotenoid content makes them a prime food source for colour enhancement in ornamental fish culture. Fairy shrimp nauplii closely resemble brine shrimp nauplii and are similar in size. The possibility of using fairy shrimp as food for aquariculture has not been explored widely. Fairy shrimp have the potential to be used as a food item for rainbowfishes and their cysts and nauplii may be useful in larval culture. They are comparable to Artemia in their nutrient contents.