That Fish Blog – Aquarium Advice and Information

No matter the profession, everyone has favorite parts of their jobs. One of my favorite “duties” is identifying the livestock we get into our store. Although we used to only offer them as “assorted” individuals, we recently started identifying the Mantis Shrimp we get in whenever possible and they’ve become my new favorite subjects!

Mantis shrimp offer some of the most varied coloration of all the marine animals that enter the hobby. The same species can have a seemingly unlimited array of color schemes depending on where they were collected, gender, surrounding habitat, and a number of other factors. Knowing what to look at as the characteristic and consistent traits is key. Sometimes, especially when they are small, it can be difficult to inspect these aspects without getting closer to the shrimp than you may like or without examining a molt or dead shrimp. Many of the available references use rather technical anatomy terms that may not be easy to understand. Here are some terms that are helpful to know and parts of the shrimp that are helpful to look at when trying to identify a mantis shrimp: Read More »

Note:  Please see Part I of this article, New Facts on Vision, Florescence and Movement, for natural history and other general information.

General

Mantis shrimp engender strong feelings among marine aquarists – to many, they are highly valued pets – responsive, complex and long-lived.  However, small specimens sometimes arrive unnoticed among live rock and make themselves unwelcome by devouring expensive fish and other creatures.  Either way, these alert predators are among the most interesting marine invertebrates available in the pet trade.

Mantis shrimp mannerisms, in my opinion, inspire one to wonder about their intelligence – they definitely seem to peer at their owners, and are very aware of all that goes on around them (see Part I of this article).  The various species exhibit a startling array of neon-like colors, and even the drabber temperate types are often interestingly patterned in tans and browns.

Aquarium Size and Physical Set Up

Although water quality is more easily managed in large aquariums, small mantis shrimp do quite well in 10 gallon aquariums.  Individuals longer than 8 inches or so do best in a tank of 20 gallons or larger.

A secure retreat, preferably a burrow below the substrate, is essential.  Despite their fearless attitude, mantis shrimp will languish and die if forced to remain in the open.  Providing a proper home will result in your seeing your pet more, not less, as it will feel secure enough to behave normally.  Artificial rocks work well. Mantis shrimp will also explore rock and coral mounds, move incredibly large amounts of sand and gravel from one place to another, and sometimes manage to create quite stable burrows of their own.

Temperature and Water Quality

Most species thrive at temperatures of 74-80 F, and at salinities of 1.020-1.022.  However, various species range from temperate to tropical waters, so please research the natural habitats of those you keep.  Setting a light timer to mimic their natural cycle (i.e. varying the cycle for temperate species) will likely benefit their over-all health.

Filtration can be quite simple for small aquariums, (i.e. an under-gravel filter).  Larger aquariums will require a suitably powerful canister or other filter.  Mantis shrimp are reasonably hardy as concerns water quality but are, like many aquatic invertebrates, quite sensitive to air-borne chemicals.  Fumes from cleaning products, paints, floor waxes and such may be introduced into even covered aquariums by the filtration system, and can be toxic to mantis shrimp.  Unexplained aquarium deaths can often be attributed to chemical poisoning.

Feeding

Depending upon the species, mantis shrimp catch their food using either of two distinct methods.  Those which “club” their food and shatter the shell or carapace (see Part I) can take small crabs, crayfish, snails, mussels and other invertebrates.  Those that grab or spear their prey are best fed shrimp, fish and aquatic worms (the “prey bashers” will accept these as well).

Mantis shrimp can be quite choosy when it comes to feeding – sometimes killing a live food item, seemingly as a territorial defense, but not consuming it.  Most will, however, adjust to unfamiliar foods over time.  They will, if you work carefully, usually accept dead food from a forceps (do not use your fingers, as serious injury can result).  This takes time and experimentation – actually, it is quite comical to see them grab an unfamiliar food, retreat into their den, and then contemptuously toss it out as unpalatable!

Tong-feeding will allow you to provide them with a more varied diet than if you relied solely upon live food.  Frozen mussels, clams, prawn, scallops, crab, squid and various fishes are all readily accepted.  Seafood (human) markets and bait stores are also excellent sources of unique food items (different shrimp, fish, snail and abalone species, for example) – including such in your pet’s diet will go a long way in promoting good health.

Captive Longevity

Mantis shrimp have lived for over 20 years in captivity.

Handling

Mantis shrimp strike out viciously with their second pair of appendages (maxillipeds) when threatened, and can cause severe injuries requiring stitches (shrimpers and divers call them “thumb splitters”).  The speed of this movement has been calculated at over 20 miles per second, and likened to the force of a small caliber bullet.  Indeed, mantis shrimp have broken aquarium glass (this is not at all common, but watch them at feeding time).

They also have a strong feeding and burrow defense response, and so may attack fingers moved in their vicinity.  Always use a tongs or other similar tool when working in the tank, and use a net if handling is necessary.

Social Groups and Breeding

It is almost impossible to house more than 1 mantis shrimp in an aquarium, unless it is very large and complex in its set up.  That being said, their breeding behavior is fascinating (please see Part I) – pairs may remain together for 20 years and care for their eggs and each other.  It would be well worthwhile to attempt to house a pair together, just be sure to have a spare tank set up in advance. 

Males may be distinguished by the presence of organs known as penes.  Used to transfer sperm, these slender structures are at the base of the last pair of walking limbs.  Males of many species are also larger than females.

Mantis shrimp larvae are planktonic in nature, and thus not likely to survive in the aquarium, but a mated pair would be most interesting to study none the less.

Thanks for your interest – we have a lot to learn about these creatures, so please pass along your observations and questions.  Until next time, Frank.  

Additional Resources

Photos of a variety of mantis shrimp species are posted at:

http://images.google.com/images?hl=en&q=mantis+shrimp+photos&um=1&ie=UTF-8

Only distantly related to shrimp, these unique, aggressive predators are actually classified within their own order, Stomatopoda. Over 400 species are known, mostly from the Indian and South Pacific Oceans. Hobbyists are often surprised to learn that one species, the 10 inch long Squilla empusa, ranges along our Atlantic Coast is for north as Cape Cod.

A flurry of new research articles on these fascinating creatures has been published recently, and it turns out that they are even more unusual than we might have suspected. I’d like to summarize some of this new information here — in my next article, I’ll write about caring for mantis shrimp in captivity.

A New and Unique Visual System
Research completed at the University of Queensland, Australia, in March of this year has demonstrated that mantis shrimp have a vision system previously unknown in any other type of animal. Utilizing precisely tilted filters in their eyes, mantis shrimp are able to perceive circular polarized light (CPL) by converted it to a linear form. CPL spirals to the left or right, and appears only as “haze” to us and other creatures (hence the need for polarized sunglasses). The filter within the mantis shrimps’ eyes functions in a similar manner to those used in certain photographic processes – only they beat us to it by about 400 million years!

CPL is reflected by male mantis shrimps’ exoskeletons, leading researchers to believe that it is used for sexual signaling. Furthermore – squid, a major mantis shrimp predator, can detect linear polarized light but not CPL. The use of CPL may, therefore, represent an ingenious strategy by which the mantis shrimp can communicate without drawing the attention of their enemies.

The World’s Most Complex Eyes
Further research in May of this year revealed that mantis shrimp possess the Animal Kingdom’s most complex eyes. Their eyes contain ten pigments sensitive to different light wavelengths, as opposed to our own three pigments. In addition to detecting CPL, mantis shrimp can also see colors ranging from ultraviolet through infrared – far more than any other creature.

Although we have yet to understand all the reasons for the evolution of such a remarkable visual system, we have some hints. Certain of the mantis shrimps’ prey, such as sand shrimp, are transparent and very difficult to see underwater. However, these shrimp are full of sugars that reflect polarized light – making them easy targets for the mantis shrimp. As if all this were not enough, mantis shrimp can also rotate each eye independently of the other, allowing for a very wide circle of vision.

Splitting Thumbs and Shattering Glass
Of more immediate concern to marine aquarists is a recent study demonstrating that a common pet trade species, the peacock mantis shrimp, can extend its hard, club-shaped front legs at speeds of over 75 feet per second. This is the fastest kick known, and explains the why we sometimes find aquariums housing mantis shrimp shattered, and a flood on the floor – the odd creatures actually generate enough force to break glass! In fact, so much pressure is exerted that the exoskeleton at the back of the leg actually wears away over time, but is replaced when the mantis shrimp molts.

This mighty thrust is made possible by a unique hinge in the leg, and was analyzed after being recorded by a camera capable of operating at 100,000 frames per second. The deadly front legs allow mantis shrimp to crack the shells of the snails and crabs upon which they feed, and to defend themselves — indeed, divers long ago christened these colorful terrors “Thumb Splitters”.

Communicating via Florescence
Although many marine creatures fluoresce (absorb one color and emit it as another), mantis shrimp are the only ones known to use fluorescence as a means of communication. This month (May, 2008) researchers at the University of North Carolina demonstrated that the bright yellow spots of the species Lysiosquillina glabriuscula were visible even at depths of over 130 feet, allowing the animals to signal each other despite the dim blue light (which would otherwise render the yellow color indistinct).

Last but not least (“last” for now, I’m sure these oddballs are hiding other secrets!) – certain species of mantis shrimp cover ground by curling into a ball and rolling downhill.

On to captive care next time – until then, please share your own observations and questions. Thanks, Frank.

A video showing just how well a pugnacious mantis shrimp can use its kicking ability is posted at:
http://www.youtube.com/watch?v=Tt55yPxTxyA&feature=related