One of the best things about reef keeping is the wide selection of readily available invertebrate, and shrimp is definitely one of them! They not only do well in most reef aquaria, they can also do good in some fish-only systems if care is taken when it comes to their tankmates and water quality.
Before discussing some of interest, lets take a look at where they fit into the Phylum Arthropoda (joint-legged animals), which also contains insects and spiders. Its Subphylum Crustacea, which of course is of more interest to aquarists, contains seven classes with over 32,000 described species and many yet undescribed species. Two of the seven, Branchiopoda and Malacostraca are of special interest, as they contain by far the majority of animals we think of as crustaceans. Those in the Class Branchiopoda are mostly freshwater or brackish species, such as brine shrimp, usually incorrectly called Artemia salina, as this species is thought to be extinct. Yet one of the known species from the San Francisco area, Artemia franciscana, is regularly cultured for the aquarium trade. Another, the very common Daphnia pulex, would be familiar to freshwater aquarists, however, its also used as a marine fish food.
Nevertheless, those in the Class Malacostraca are of far more interest as it contains crabs, lobsters, prawns, shrimp, and crayfish. It's further divided into three subclasses, Phyllocarida, Hoplocarida and Eumalacostraca. As for Phyllocarida, its mostly ancient/primitive creatures, with most extinct. In the Subclass Hoplocarida, its Order Stomatopda contains those dreaded mantis shrimps that are often undesirable in our aquariums. They look quite similar to their terrestrial counterpart the "Praying Mantis" hence their name. These are awesome predators and are armed with powerful appendages that can destroy hard-shelled prey. In fact, they can easily smash the shells of snails, crabs, clams, easily capture fish, eat feather dusters/hard tube worms, and can split your finger right down the middle!
I've maintained Odontodactylus scyallarus, the brilliantly colored Peacock Mantis Shrimp, which can get as large as 18 inches (45 cm), in a dedicated 20-gallon aquarium with lots of rubble and a shallow sand bottom. This extremely interesting creature hails from the Indo-Pacific and did well in average water quality with daily feedings of meaty foodstuffs. Even though it made for an extremely interesting display, it was at times quite noisy! As many know, pistol shrimp make a sound similar to a single 22 caliber shot when disturbed or hunting prey. Mantis shrimp, however, also make a noise, yet theirs is more like a machine gun, i.e., having a rapid series of slightly less loud shots. In fact, it's a good way to tell whether it's a mantis or pistol shrimp hiding in your aquarium!
In the Subclass Eumalacostraca, there are several superorders, two of which are of interest to marine aquarists. Its Superorder Peracarida contains small bottom-dwelling isopods and amphipods, along with small opossum shrimps we know as mysid shrimps.
The Superorder Eucarida contains two orders of significance. Order Euphausiacea contains the Pacific krill (Euphausia pacifica), which is an excellent foodstuff, either frozen or freeze-dried for our fish. And probably the most interesting is the Order Decapoda (meaning ten feet), which includes shrimps, prawns, lobsters, hermit crabs, and true crabs, and is composed of about 68 families containing almost 10,000 species.
This order is further divided into two suborders, Dendrobranchiata and Pleocyemata where those within it are classified by the structure of the gills and legs, and the way larvae develop. Those in the Suborder Dendrobranchiata release their eggs into the water and hatch as nauplii. And if shrimp are a people food in your household, a whole industry has been built around the culture of 'prawns' in this suborder. As for those in the Suborder Pleocyemata, its members cement their eggs to their pleopods (abdominal appendages) until they hatch, and these are of more interest to aquarists.
And once we move into the Suborder Pleocyemata, there are numerous 'infraorders' dedicated to various types of creatures, e.g., shrimp, lobsters, crabs, etc., and two have special interest if 'ornamental' type shrimp are of interest. In the Infrorder Stenopodidea, Family Stenopodidea, there's a very familiar species called the Banded Coral/Boxer shrimp Stenopus hispidus. However, it's not really considered a shrimp! It's considered more a lobster-like creature. These are circumtropical animals and even though they do set up cleaning stations in the wild, it's an infrequent happening in aquaria. These must be maintained singly or in mated pairs in aquaria, as they will kill same sex members. The female has a heavier body and carries her eggs for about two weeks under her shell. The eggs can usually be seen through the shell where they are first a yellow color, then turn a light green. When the female molts, about every 16 days, the male fertilizes the eggs. The eggs are hatched in the female's mouth in small numbers about two weeks later, and released into the water column. The babies are half the size of newly hatched brine shrimp and can live on their yolk sac for three days. Rotifers are a good food supply until the babies can take larger food. The adults will accept defrosted pieces of clam, shrimp, krill, fresh fish flesh, or live brine shrimp. They have a temperature range of 71 to 83°F (21-28°C), and are one of the favorites among aquarists. In fact, they are easily kept in reef aquariums when there are sufficient caves and hiding places. Yet, can do harm to corals and anemones when there's insufficient food. Attains a maximum size of 4 inches (10 cm).
Once we move into the Infraorder Caridea, more familiar 'true shrimp' genera begin to show up. The family Hippolytidae in this infraorder probably contains the most well-known aquarium genera of which the genus Lysmata contains the 'cleaner shrimp' often called the Scarlet Cleaner shrimp, Lysmata amboinensis. It's probably the most popular of all marine aquarist ornamental shrimp. And that's because it's not only very pretty, it's a prolific cleaner of fish parasites, almost always setting up cleaning stations and trying to entice customers by waving its long white antennae. This beauty has two red longitudinal stripes separated by a white stripe and hails from the tropical Indo-Pacific and Red Sea. This 3 inch (8 cm) cleaner shrimp can be kept in small groups and will come directly onto your hand to take pieces of clam, shrimp, krill, mussels, mysis, fresh fish flesh and the hair off the back of your hand. It's frequently in view during the day and may steal food from corals, but does not appear to be destructive. Since these shrimp are hermaphroditic spawners (possess both male and female sex organs), all adult members of the group produce eggs and are fertilized by another member of the group. Therefore, any two of these shrimp is sufficient to propagate the species, if they like each other! Readily breeds in the home aquarium, yet availability of captive-bred specimens is still in question. They do however; seem to be sensitive to temperatures above the low eighties. There's also an Atlantic morph, L. grabhami, that is almost an exact copy, except its white stripe goes all the way into the tail, whereas the central body white stripe on L. amboinensis stops at the top of the tail.
Another favorite in this genus, although more expensive, is the Blood Red Shrimp Lysmata debelius, which hails from the Central Indo-Pacific from the Chagos Archipelago to Indonesia. It basically has the same husbandry as those above, but is extremely shy and spends most of its time hiding. In fact, in large aquariums, you may lose sight of these 2 inch (5 cm) shrimp for months, and because of that, are difficult to make sure its getting the food its needs to stay healthy.
Still in this genus, the Peppermint Shrimp Lysmata wurdemanni, has become a favorite if for no other reason than it's a very good consumer of unwanted Aiptasia sp. anemones. In fact, I've seen a newly added group head directly for these anemones in my aquarium and stay there until they were all eaten! It is not necessary to directly feed them, as they mostly hide during the day, usually on the underside of elevated rocks, and scavenge for food during the night. Unfortunately, they have a taste for zooanthids such as Parazoanthus gracillis, which is generally called Yellow Polyps by aquarists. This shrimp molts about every seven months. It begins life as a male, yet most change to females, however, they retain the male ducts and produce sperm. The females, therefore, are able to incubate their own embryos without the help of a male. It has successfully been captive bred.
As for molting in general, i.e., the shedding of its shell-like exterior (exoskeleton), it's an extremely important growth aspect for all shrimp. To grow larger, shrimp must shed this exoskeleton, as it will not stretch. Periodically, the shell-like covering begins to dissolve and separates from the body tissue while a new shell develops underneath. When the process completes, the shrimp climbs out of the old exterior covering and then takes up water, stretching the new soft covering to fit its now larger body. When finished, the new covering forms a hard exoskeleton. Keep in mind they are defenseless at molting time, therefore need secure hiding places that predators cannot reach.
Keep in mind all shrimp should be slowly acclimated to their new surroundings as they have a tendency to go into shock when entering an aquarium where water parameters are only slightly different from the shipping container. Temperature and especially Specific Gravity (S.G.) should be the same before transferring them into their permanent home. Contrary to what you may have heard, shrimp of any kind should never be given a freshwater bath to kill parasites prior to being added to the aquarium. It 'will' kill them, as they are very sensitive to changes in osmotic pressure. And as with all shrimp, low alkalinity, calcium, iodine and especially low magnesium levels can interfere with the molting process. In fact, magnesium 'must' be maintained at the proper level in relation to the S.G., or the molting process will not complete (per. com. Dr. Vincent Hargreaves). The lack of proper magnesium level is probably the main reason why many aquarists fail to maintain shrimp over the long term!
And as for water quality requirements; Calcium 380 - 430 mg/l; Alkalinity 3.5 - 4.5 meq/l; pH 8.1 - 8.2; Specific Gravity 1.024 - 1.026, Mg