01 · One shrimp
Opae ula
Halocaridina rubra
ʻŌpae means shrimp; ʻula means red.
As a shrimp
About half an inch, found only in Hawaii, in anchialine pools: brackish pools near the sea, linked to it underground. It can live 10 to 15 years.
Behaviour
Scrapes the crust of algae and bacteria off rock, and filters food from the water with fine bristles on its legs.
Its job here
Lives on the bowl's own film of algae and bacteria, so the bowl needs little food and no filter.
Facts
- Size
- About ½ in
- From
- Hawaii only
- Lives
- 10 to 15 years
- Water
- Brackish, specific gravity 1.008 to 1.018; 68 to 82 °F
National Park Service, Anchialine pools; Wikipedia, Halocaridina rubra; Shrimp Science, opae ula tank
BrackishOpae ula shrimp bowl
A tide pool in a bowl.
1.6 gallons of brackish water for opae ula, the tiny red shrimp of Hawaiʻi's lava pools.
01The bowl
A small world.
A round glass bowl, about 9 inches wide and 8 tall, with a 6 inch opening.
02Substrate
A black floor.
Inert substrate: it changes nothing in the water.
03Hardscape
Lava, fans and pebbles.
Lava rock, two small natural sea fans, and white calcium carbonate pebbles.
04Algae
Something green.
A clump of Chaetomorpha and a slow-growing algae ball.
05Water
Half sea.
Brackish salt in distilled water, to a specific gravity of 1.010.
06Light
Twelve hours of sun.
A 12 W grow light on a 12-hour timer feeds the film the shrimp eat.
01Anchialine pools
Born in lava.
Opae ula come from anchialine pools in Hawaiʻi: water caught in lava rock near the shore.
Rare
Hawaiʻi is the only US state that has them.
02Salinity
Not fresh. Not sea.
Brackish is fresh water with a little sea in it. Keepers measure the salt as specific gravity: how heavy the water is next to pure water.
About a third of sea
Brackish salt in distilled water, to 1.010.
03The water cycle
Only light goes in.
No filter, no heater
Algae, bacteria and shrimp recycle the rest.
Rock that holds the pH
White calcium carbonate pebbles keep it above 8. No wood: it pulls the pH down.
04Why so simple
No plants. No water changes.
Food grows on the rock
In Hawaiʻi they scrape the crust of algae and bacteria off the lava. Here too, that film is most of what they eat: the light grows it, the shrimp graze it.
No plants needed
Plants are not their food, and most aquarium plants are freshwater plants. The green here is Chaetomorpha, a sea algae that also lives in brackish water.
Very little waste
A few half-inch shrimp, fed once every two to four weeks, make very little waste. The algae and bacteria use it up.
Top up, don't change
Water evaporates and the salt stays behind. So only distilled water goes back in, before about a tenth is gone. No routine water changes.
04Halocaridina rubra
Small, red, long-lived.
ʻŌpae means shrimp, ʻula means red. Hawaiʻi's state shrimp.
00Livestock
Red, and patient.
02 · The colony
The colony
Halocaridina rubra
Slow, and long lived.
Eggs
A female carries about 12 eggs for 30 to 38 days, once or twice a year.
Larvae
The larvae are about ⅛ inch, and take about seven weeks to reach adult shape.
Patience
A bowl colony grows slowly; each shrimp lives for years.
05Timeline
Film first. Shrimp later.
- NowSetting up
Substrate, rock, fans, pebbles and salt water.
- A few weeksThe bowl matures
Bacteria settle in; the biofilm grows.
- About Nov 9Twelve opae ula
In about 17 days.
06The tanks
Five tanks, one house.
00Gear list
What it is made of.
The gear list
- Glass bowl1.6 gal
- Black substrateA thin floor
- Lava rockRough rock for the film to grow on
- Calcium carbonate pebblesCalcium for moulting, and alkaline water
- Sea fansSomewhere to climb
- ChaetomorphaFine green macroalgae
- Marine salt in distilled waterMixed to about 1.010
- RefractometerReads the salt
- Small LED lightAbout 12 hours a day