Opae Ula Care Guide - Habitat, Feeding & Breeding Tips

Opae Ula, also known as Hawaiian red shrimp, are tiny, long-lived brackish-water shrimp belonging to the atyid family. Their translucent bodies are usually marked with rich red to rusty-brown colour, although the intensity can vary with age, diet, genetics and surroundings. A pale dorsal stripe or lighter markings may be visible along the back.

These shrimp are peaceful, unobtrusive animals that spend much of their time grazing on algae, microorganisms and biofilm. They may gather in groups on rockwork, glass and other surfaces, becoming more active when food is available. Their small size and calm nature make them especially appealing for compact specialist aquariums.

In the wild, Opae Ula live in anchialine habitats: landlocked pools connected to the sea through porous volcanic rock. These unusual environments can experience changes in salinity and water level, while lava provides abundant crevices and surfaces for grazing. The shrimp are adapted to brackish conditions rather than ordinary freshwater.

Halocaridina rubra is noted for its exceptional longevity compared with many ornamental shrimp. With stable conditions and protection from predators, individuals can live for many years, and established colonies may gradually grow through successful reproduction.

Opae Ula are endemic to the Hawaiian Islands in the central Pacific Ocean. They inhabit anchialine pools and lava-rock groundwater systems, especially on the islands of Hawaii, Maui, Oahu and Molokai.

A colony can be maintained in a mature aquarium of around 5–10 litres, although 10 litres or more provides greater stability and room for growth. A practical setup is approximately 30 × 20 × 20 cm or larger, with a secure cover to limit evaporation. Use marine or aragonite-based sand or fine inert substrate, porous lava rock and other hard surfaces for grazing and shelter. Gentle filtration or aeration is suitable, while strong currents, untreated metals, copper-based medications and freshwater top-ups should be avoided.

Up to about 1.5 cm (0.6 in) in total length; females are generally larger and deeper-bodied than males.

Opae Ula naturally graze on algae, bacterial films, microorganisms and organic particles that collect on rock surfaces. In an established aquarium, mature biofilm and algae may provide much of their nutrition, supplemented occasionally with a very small amount of shrimp food, spirulina-based food or other suitable algae-rich foods. Overfeeding can quickly pollute a small aquarium, so only tiny portions are needed.

Opae Ula are best kept in a species-only aquarium or with other peaceful organisms that share their brackish requirements. Small, non-predatory snails and carefully selected brackish-tolerant microorganisms may be compatible, but most fish will eat the shrimp or their young. Avoid freshwater community fish, aggressive species, crabs and large invertebrates, which may harass or consume them.

Opae Ula breed readily when settled in a mature, stable brackish aquarium. Females carry fertilised eggs beneath the abdomen, and the eggs hatch into miniature shrimp rather than free-swimming larvae, so there is no need for a separate rearing tank. Provide gentle water movement, algae and biofilm, and avoid exposing the adults or young to freshwater. Breeding is slow, with females producing relatively small broods at intervals rather than spawning large numbers at once.

Females are usually larger, broader and more rounded through the abdomen, particularly when carrying eggs. Males tend to be smaller and slimmer, with a narrower abdomen.