That Fish Blog – Aquarium Advice and Information

Please welcome back Frank Indiviglio with another excellent article.

Introduction – A Most Captivating Fish
Seahorses, armor-plated and prehensile-tailed, and equipped with independently-moving eyes and fins that flutter like wings, seem to stretch the limit of what might conceivably be called “a fish”.  Add to this the phenomenon of “male pregnancy” (the male incubates the eggs in a pouch and adjusts the salinity of the water therein as needed; please see my article posted on this blog on June 27, 2008 for more details) and the fact that seahorses change color and can grow and discard filamentous appendages, and you can easily see why they have long attracted marine aquarists.  All of the nearly 130 species (Family Syngnathidae) are, however, strict live food specialists, and rarely thrive on the brine shrimp-based diet commonly offered to them in captivity.

The two species highlighted in this article (Please see Part I, The Atlantic Seahorse, published last week) were chosen because, of all, they are the most likely to do well on diets that are within the means of most aquarists.  Please do not be tempted to try other species until you are well-experienced with the following animals.  I will focus here on points unique to seahorse husbandry – water quality and filtration should be managed as for other marine fishes (please see related articles posted on this blog).
Dwarf Seahorse, Hippocampus zosterae

Description and Habitat
“Seapony” might be a more appropriate name for this diminutive creature, which, at an adult length of 0.9 inches, is only slightly larger than the smallest known species, Denise’s pygmy seahorse (please see below).  Ranging from Florida to the Bahamas, the dwarf seahorse may be white, yellow, green or black in color.  It dwells in sea grass beds, so much so that the species name, “zosterae”, is drawn from that of the plant with which it is most often associated.  Northern populations were formerly considered to be a separate species, H. regulus.

An Ideal “First Seahorse”
In sharp contrast to larger fishes, dwarf seahorses offer us the opportunity to observe nearly all of their natural behaviors in captivity.  Due to their small size, they adjust readily to the confines of aquarium life.  Three pairs in a 15 gallon tank will reward you with a display of activities not often observed among captive seahorses of other species.   As a consequence, their captive husbandry is well understood, and many specimens in the trade are commercially produced.  This is an important consideration at a time when many seahorse species are in sharp decline (please see below).

Interest in this charming creature peaked here in the 1960’s and early 70’s, when they were advertised for sale in the backs of magazines.  My grandfather, who kept marine fishes even before that time, so aroused my interest in them that I eventually wrote a book on the care and natural history of seahorses  (please see below).

The Key to Feeding Dwarf Seahorses
Dwarf seahorses are one of the only seahorse species that will thrive on a diet consisting solely of enriched brine shrimp.  They will, however, appreciate an occasional meal of tiny, wild caught invertebrates – thin meshed “plankton nets,” (available from biological supply houses) drawn through shallow marine waters will yield a wealth of valuable food items.  “Enriched” brine shrimp are those that have been allowed to feed for a few days before themselves being given to the seahorses.  This process increases the shrimps’ nutritional value, and is indispensable if one is to succeed in keeping dwarf seahorses.  Therefore, brine shrimp intended as seahorse food should be given Brightwell Aquatic’s Phyto-Green, or a similar product, for several days.

Breeding and Other Considerations
In common with all their relatives, dwarf seahorses require calm water and suitable “hitching posts” upon which to wrap their tails.  There is some evidence that wild seahorses consistently utilize the same hitching sites, so their aquarium’s décor should not be re-arranged once they have been introduced.  Captive reproduction is a definite possibility – the tiny young can take only newly-hatched brine shrimp, so be sure to set up a brine shrimp hatchery  in advance.

Tiny, Newly Discovered Specialists
The Pygmy Seahorse, Hippocampus bargibanti, first described in 1970, seems to live on only 2 species of gorgonians (soft corals) of the genus Muricella.  So closely does it resemble the coral’s polyps that the individual which led to the first description of the species was not discovered until it was seen on a coral that had been placed in an aquarium several days earlier!  At 0.8 inches in length, it was the smallest known species until the discovery, in 2003, of Indonesia’s Denise’s pygmy seahorse.  Adults of this minute creature are a mere 0.6 inches long.

As mentioned, I became so enamored of these unique fishes that I wrote a book on their care and natural history – if you have a chance to read it, please forward your thoughts and suggestions to me.   Until then, please write in with your questions and comments.  Thanks, until next time, Frank.

Project Seahorse is the world’s premier seahorse conservation and research organization.  A wealth of information is available at their web site:
http://seahorse.fisheries.ubc.ca/who.html

Thanks for the great article Frank,

Until Next Time,

Dave

Introduction
Today I would like to discuss a large, temperate water seahorse that can be kept and even bred in captivity by those willing to devote the necessary time and effort to its care.

Note: Please see my article posted on this blog on June 27, 2008 for information concerning new research into the phenomenon of “male pregnancy” in seahorses.

A Temperate Seahorse
Most people consider seahorses to be tropical in origin, and may be surprised to learn that the Atlantic seahorse ranges as far north as Nova Scotia, the waters of which are decidedly “un-tropical”.  It also occurs south to Venezuela, and it is the only seahorse to dwell north of North Carolina along our eastern seaboard.

Found from the shoreline to depths of over 230 feet, this weak swimmer somehow manages to survive in areas of strong tidal activity.  I have collected Atlantic seahorses attached to clumps of marine algae being swept along by very strong currents.  Mated pairs are believed to establish stable territories, but I cannot imagine how they can accomplish this in the turbulent waters they sometimes inhabit.  I imagine that individuals in such populations move to quiet bays during the breeding season – any information you might have concerning this would be most appreciated.

Feeding Atlantic Seahorses
The Atlantic seahorse’s rather large size, to 7.3 inches, allows it to take a wide variety of prey, including small shrimps, blackworms and fish fry. This, coupled with the fact that many individuals can be tempted to eat frozen foods moved about in a life-like manner, makes the Atlantic seahorse a good (but still delicate) candidate for experienced aquarists.

In addition to the foods mentioned above, Atlantic seahorses that I have kept were extremely fond of amphipods (scuds or side-swimmers), sand hoppers, seed shrimp and sand shrimp that I seined in local marine waters.  Their reactions to these food items were quite intense, much more so than to the fish fry, brine shrimp and opossum shrimp (Mysids) that made up the bulk of their diet.

I urge anyone attempting to keep seahorses to collect live foods whenever possible.  It is especially advantageous to maintain native species, as you have a better chance of providing these with a balanced diet based on natural, wild-caught prey (an extremely important consideration when keeping delicate live-food specialists).

Several specimens under my care also accepted frozen clams, shrimp and scallops.  This requires a conditioning period, and is best accomplished with young animals or long-term captives.  Frozen food is initially mixed in with live food, and kept in motion via the filter outflow (or, for the really dedicated, water squirted from a turkey baster).  You may also wish to experiment with freeze dried krill and similar foods.

Black mollies breed readily, and few pairs should be maintained as a food source for Atlantic seahorses.  Their fry, which will survive the transition to salt water if slowly acclimated, are usually readily consumed by the seahorses.

Other fresh-water food animals worth trying include fairy shrimp, bloodworms (midge larvae, Chironomus spp.), blackworms, micro-worms, grindal worms and white worms.  Please bear in mind that these animals expire and decompose rapidly in salt water, and that they do not likely provide complete nutrition in and of themselves.

Seahorse Companions
This species presents a limited exception to the general rule that seahorses should not be housed with other creatures.  Actively swimming fishes should be avoided, as they will out-compete the seahorses for food.  However, Atlantic seahorses will get along well with northern pipefish (these may be seined from eel grass beds where legal), hermit crabs, sea stars, small spider and horseshoe crabs and fifteen-spined sticklebacks, Spinachia spinachia (these last feed fairly slowly, but watch the seahorses’ intake carefully).

A quite interesting community tank can be built around the Atlantic seahorse and some of the creatures that share its habitat.  As these are generally over-looked by aquarists, the potential to learn something new is very great.  I would be most pleased if you shared your observations with me.

Other Considerations
Hailing as they do from temperate waters, Atlantic seahorses from northern populations should be kept in unheated aquariums.  Breeding (which I’ll cover in depth in the future) will be more likely if they are provided with natural fluctuations in day length and temperature.  This can be accomplished by situating their aquarium near a window (beware of over-heating during the summer) or by installing a light timer to regulate day length.  Atlantic seahorses may give birth to over 300 young.

Seahorses in Peril
Untold millions of seahorses are collected annually for use in Chinese and South Asian traditional medical practices, and for the curio and pet trade.  Many more perish due to habitat loss and as “by-catch” in commercial fishing operations.  Please be sure to purchase only captive-bred seahorses.

I became so enamored of these unique fishes that I wrote a book on their care and natural history – if you have a chance to read it, please forward your thoughts and suggestions to me.  I’ll write more about seahorses and their relatives in future articles.  Until then, please write in with your questions and comments.  Thanks, until next time, Frank.

Information about a reintroduction program for the Atlantic seahorse on Long Island, NY is posted at:
http://counties.cce.cornell.edu/suffolk/habitat_restoration/seagrassli/ecology/fauna_flora/seahorses.html

Seahorse (Hippocampus erectus). Taken at the New England Aquarium (Boston, MA, December 2006. Copyright © 2006 Steven G. Johnson and donated to Wikipedia under GFDL and CC-by-SA

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

Surprising new information about aquatic invertebrates is uncovered every day…the following is a small sample, which I’ll add to from time to time.  Please see Part I of this article as well.

Good and Bad Pets

The venom of the tiny blue-ringed octopus, Hapalochlaena maculosa, is one of the most toxic known, with the amount delivered in a single bite being sufficient to kill an adult person.  Yet this creature occasionally appears for sale in the pet trade – learn to identify and avoid it!

Giant water bugs (Family Belostomatidae) can be collected throughout the USA and make interesting, if aggressive (they can inflict a painful bite), aquarium subjects. The males of many species carry the eggs about on their backs.  A species I collected in Venezuela topped 4 inches in length, and regularly consumed small frogs.  Another I came across at Japan’s Kaiyukan Aquarium easily subdued a 3 inch long minnow.  Please look for my future article on aquatic insects.

Most corals rely upon minute creatures for their food and are difficult to maintain in aquariums.  However, tooth coral (Cynarina spp.) accept pieces of shrimp and other large food items, and should be considered as a first choice by those new to coral-keeping.

Jellyfishes are not usually available in the pet trade, and are quite delicate in captivity.  One exception is the upside-down jellyfish, Cassiopeia andromeda.  In contrast to all others, it rarely swims but rather rests in a “head down” position, with the tentacles trailing above.  Given intense lighting (it relies upon symbiotic algae) and plenty of brine shrimp, it often thrives in the aquarium.

Catching and Storing Food

Surprisingly, some spiders have adopted an aquatic lifestyle, and several of these adapt well to aquarium life. North America’s fishing spiders, Dolomedes spp., float on the water’s surface and dangle a leg below to lure small fish within reach.  The European diving bell spider, Argyroneta aquatica, takes aquatic life a step further – it lives in a submerged, air-filled retreat from which it launches attacks on passing fish and invertebrates.  Please look for my future article on these unusual creatures.

Several crabs have interesting ways of “planning for the future”.  Atlantic spider crabs, Libinia emarginata, stuff marine algae into crevices on their shells, effectively camouflaging themselves and storing food at the same time (those I have kept abandon this habit when they reach 3 inches in size).  The ever-popular arrow crab, Sterorhynchus seticornis, impales bits of food, to be consumed in the future, on the pointed end of its carapace.

How Big…How Old?

Crabs, lobsters and their relatives (Order Decapoda) are among the most important aquarium and food-trade invertebrates.  The legs of the Japanese spider crab, Macrocheira kaempferi, the largest of the group, may span 13 feet.  Both it and the American lobster, Homarus americanus (at 60+ pounds, the heaviest Decapod) may live for 100 years. The largest freshwater species is the 9 pound New Zealand crayfish, Astacopsis gouldi.

At 4.5 feet across and up to 750 pounds in weight, the South Pacific’s giant clam, Tridacna gigas, is the largest of the world’s 6,000+ bivalves (clams, oysters and relatives).  It relies upon commensal green algae for much of its food, and produces the world’s largest pearls – one of which weighed in at 14 pounds!

Many mollusks (snails, clams and their relatives) lay down growth rings, which appear as irregularly-spaced lines on the shell.  Much as with trees and turtles, these lines can often be used to determine these creatures’ ages.

Defense and Survival

Although largely aquatic, several species of North American crayfish, known as chimney crayfish, exploit terrestrial habitats.  They live in wet meadows and dig tunnels, which may exceed 10 feet in length, to the water table.  Recently, it was discovered that these water-filled retreats provide vital breeding sites for salamanders during droughts.

Sea urchins are interesting aquarium inhabitants, but most aquarists find them rather unresponsive.  However, they react immediately to the shadow thrown by a hand or other object passing overhead by orienting their spines towards the disturbance.  This is a defensive reaction, designed to direct the sharp spines towards an oncoming fish or other predator.

I look forward to hearing about your own observations concerning aquatic invertebrates, and to answering your questions.  Thanks…until next time, Frank.

A great deal of interesting information concerning marine, fresh water and terrestrial in invertebrates of the Pacific Basin is available at the following web site:

http://pbin.nbii.gov/marinverts/index.asp

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