The red feeder shrimp are easy to keep in a small separate tank indefinitely and they will breed under the right conditions, but they reproduce so slowly it is extremely difficult to culture them in any quantity. It can be done, but the larval shrimp undergo many different stages of development and raising them is very, very challenging. It isn’t really practical for the home hobbyist.
I have no idea how to sex them, but that shouldn’t really be necessary — they are colonial shrimp that live together in large groups, so if you’re going to be keeping a few dozen of them as seahorse food, you can rest assured that both males and females will be present and that natural reproduction will occur. Getting them to breed isn’t the problem; rather, it’s their low fecundity — the fact that they spawn only a handful of times each year and reduce such low numbers of young each time they spawn — that makes it difficult to raise them in any numbers at all.
Here is some additional information about these fascinating little shrimp that will explain the conditions they prefer for keeping them as potential seahorse food:
You will find the red feeder shrimp (Halocaridina rubra) to be easy to keep and relatively undemanding to culture, although their numbers build up very gradually due to their naturally slow rate of reproduction.
Red feeder shrimp or volcano shrimp, as they are sometimes known, prefer brackish conditions and breed best at reduced salinity (1.0145-1.0168) but they adapt well to full strength saltwater and will survive indefinitely is a marine aquarium. They are a perfect "feed-and-forget" treat for large seahorses! As a rule they don’t need a great deal of room. The size of the tank you’ll need depends on the number of shrimp your dealing with and whether you want to maintain and ongoing culture or simple keep them alive until needed. A 5-10 gallon tank will generally suffice for 500-600 of these shrimp and biological filtration of some sort is desirable for keeping them long term. A simple sponge filter will do.
RED FEEDER SHRIMP from Hawaii (Halocaridina rubra)
* Excellent nutritional value
* Irresistible to all the greater seahorses.
* Feed-and-Forget — lasts forever in saltwater!
* Easy to enrich.
* Simple to gut-load.
* Can be cultured using simple techniques and the most basic setups.
* Reproduces slowly; difficult to build up a large population.
Specific gravity: 1.0145-1.0168; pH: 8.0-8.3
Temperature: 68 degrees F – 73 degrees F (20 degrees C – 23 degrees C)
These fabulous little feeder shrimp can be kept indefinitely in a spare 2-10 gallon tank, or even a clean, plastic bucket, that has been filled with clean saltwater and equipped with an airstone for aeration. Neither a heater nor a fancy filtration system is required. They thrive at room temp and reduced salinity (1.015-1.016), and all they require is an airstone (or a simple air-operated foam filter at most) to keep the water oxygenated, with perhaps a little coral rubble as substrate and a clump or two of macroalgae (sea lettuce, Ogo, Gracilaria) to shelter in. They’re easy to feed — they feed primarily on algal mats and bacteria — but they will accept vegetable-based flake foods and pellets such as various Spirulina products. They are filter feeders and can also be fed with yeast or commercially prepared foods for filter-feeding invertebrates. Many people find an easy way to feed them is to place a small piece of algae-encrusted live rock in their holding tank; once they clean it off, simply replace it with a new piece of algae rock. But if you want to culture them, I’d recommend ordering the special shrimp food formulated just for them when you order your feeder shrimp from Hawaii. It’s designed to meet all their needs and requirements.
These tiny red feeder shrimp (Halocaridina rubra) are native to Hawaii where they inhabit underground lava tubes. Brackish pools collect in the cracks, crevices and depressions in the lava below the water table, thus forming the habitat for the shrimp. The brackish water that fills these pools consists of intrusive seawater diluted by freshwater that percolates downward. Because of their lava-tube habit, they are sometimes called Hawaiian Volcano Shrimp.
Native Hawaiians call them Opa’e-ula, and they are unique among the several different species anchialine pond shrimp in being small, social, herbivorous shrimp that feed mainly on algae and bacteria. They are known to feed on insects that drown in the lava tubes. When conditions are favorable, they may feed en masse at the surface in swarms of countless individuals that turn the water red.
Halocaridina rubra look like miniature, bite-size Peppermint Shrimp, and all seahorses save the miniature species go absolutely nuts for them! They are very nutritious and eat a varied, omnivorous diet. They are perfect for seahorses in every way.
Unfortunately, it is very difficult to culture these shrimp in any quantity, since they reproduce slowly and the females only carry 12 to 14 eggs. They spawn but 4 or 5 times and produce an average of only 5-10 larvae per spawn. The larvae hatch as free-swimming, yolked zoeae after a brooding period of 38 days. Larval development is abbreviated with four zoeal stages and one megalopial stage occurring before they reach the first juvenile stage. Duration of the larval stages in the aquarium is 24 to 27 days at 22 to 23 degrees C.
Like other shrimp, it is the complicated larval developmental period they undergo, with multiple zoea and megalops stages, that makes the larvae difficult to raise, RJ. However, it can be accomplished the same way other decorative shrimp such as peppermint shrimp (Lysmata wurdemanni) are raised. There is a very interesting and informative book that explains exactly how to go about raising such shrimp that I recommend you read. It’s called "How To Raise & Train Your Peppermint Shrimp" by April Kirkendoll and they can be obtained at the following URL:
You’ll find lots of excellent information on raising peppermint shrimp in April’s book that will apply equally well to your volcano shrimp if you really want to give it a try, RJ.
Best wishes with all of your fishes!