Home | Saltwater Aquariums (page 30)

Category Archives: Saltwater Aquariums

Feed Subscription

Contains articles featuring information, advice or answering questions regarding saltwater aquariums, livestock or equipment.

Global Warming, is it really to blame?

Please welcome Cory Shank to That Fish Blog. Cory is an on-staff marine biologist here and our resident “Coral Guy.” Take a look below to read his thoughts on the future of wild coral. Cory Shank

Corals reefs are enjoyed by millions of people each year, while on vacation or in the comforts of their own homes. Coral reefs are the most biodiverse ecosystems in the ocean and arguably in the world. It is well known that coral reefs are beginning to decline world-wide, from Australia to the Florida coastline. This is a major concern for industries economically involved, the aquarium trade, global tourism, and commercial food fisherman. The problem is, how do we stop this disturbing decline when we don’t know enough about the issues causing it?


The hype over global warming has many believing that the water temperature increases are causing the coral degradation. Water temperature plays a major role in maintaining the health of a coral reef ecosystem. In our aquariums, we use fans and chillers to keep our tanks at a desirable temperature, but reefs depend on natural currents and climatic conditions. In the past, the world climate has warmed much faster and more dramatically and the corals have lived on. The El Nino event of 1997-98 caused massive coral bleaching throughout the world’s coral reefs. Ten years later, many of these areas have recovered and are showing signs of expansion. So it is reasonable to believe that this cannot be the only reason behind the coral destruction.


So, what else can be going on? I was in Hawaii recently and spent most of my time in the water observing the wonderful fish, corals, and invertebrates. I noticed quite a bit of new coral growth and plenty of fish. However, there were areas that were not doing so well. Along the main highway, just off shore, were large coral colonies covered in filamentous algae and diatoms, not at all what the reefs looked like 5-10 miles offshoreReef system.  There the corals were thriving, and no algae could be seen. Along the shoreline, there are drainage pipes coming from the roadways and further up the mountains. This is where all of the runoff ends up. With more development come more impervious surfaces, chemicals, soil, and debris that enter the oceans, increasing the amount of siltation that occurs from the breakdown of coastal buffer zones. The soil and debris enter the ocean, choking out the coral. This also adds nutrients to the water, leading to enhanced algae growth, which also chokes out the coral. Coastal development is occurring all over the tropics, and new resorts and hotels and homes are being built every year, increasing to the problem.


With the increasing amount of hotels and resorts near where the coral reefs are located,  tourism poses a new wave of problematic issues. There are snorkelers and divers who may not respect the reefs and act irresponsibly, stepping on the corals, catching the fish, and polluting the waters. While in Hawaii and the Florida Keys on separate trips, I have witnessed people standing on corals with their snorkel fins not considering the damage they may be causing. The amount of trash floating around, stuck in between corals, or just buried in the sand is appalling and virtually unavoidable these days.


If Global Warming is occurring, causing the sea surface temperatures to rise, then everyone needs to step up and start protecting the reefs in any way that we can. At the current rate of degradation, a large percentage of coral reefs may disappear in the next 10 to 20 years. This will have devastating economic impact on the locals populations and to everyone else in the world that relies on income from those areas around the world.   Skyrocketing prices on everything from ornamental aquarium specimens to the shrimp for your picnic or barbecue will be the likely result, as these things become harder to come by. It is going to take a worldwide effort to help save the coral reefs, and we are running out of time, so please do your part and help protect our most biodiverse ecosystem.


Thanks for the great article Cory. Please write in with your thoughts or observations on this important topic.

Until next blog,



Mantis Shrimp (Order: Stomatopoda) – Part II, Care in Captivity

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


GeneralMantis Shrimp

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.



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.



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:


Unusual Facts about Aquatic Invertebrates, Part II


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.Spider Crab Exhibit in Japan



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:



Unusual Facts about Aquatic Invertebrates

horseshoe crab
Knowing where to start and stop when it comes to writing about invertebrates is a real problem – any single group could keep one occupied for a lifetime. Today I’d like to highlight some interesting facts concerning a few commonly kept types and their relatives. I’ll add to this from time to time.

Invertebrates (animals without backbones) account for approximately 97% of the world’s animal species, yet we have no idea of their total numbers. The smallest are invisible to the naked eye while the largest, giant squid, may exceed 60 feet in length.

Nearly every injectable drug manufactured in the USA is tested for bacterial contamination with a chemical extracted from horseshoe crab blood (synthetics do not work as well). Several states are restricting the collection of these animals (often used as fertilizer!) and requiring that they be released after blood specimens are taken.

Invertebrates have colonized every habitat imaginable, from freezing Antarctic seas to the boiling hot water of geysers. The sponges, crabs, tubeworms and others living near deep sea vents form the only animal community that does not rely upon photosynthesis as the basis of the food chain (bacteria that consume methane function as “plants”).

Despite being a creature of legend for centuries, the giant squid, Architeuthis sp., was not captured on film until 2004. Two years later, the same Japanese scientists that filmed the animal caught a specimen on a fishing line, thus giving the world its first view of a living giant squid.

Eating and Being Eaten
Despite radically different appearances, jellyfishes, sea anemones and corals are closely related (Phylum Cnideria). All gather food and excrete wastes through a common opening, and overcome their prey with stinging cells.

Jellyfish, although comprised largely (95%) of water, are able to snare prey as large as small fishes. Surprisingly, they form the bulk of the diet of many huge sea creatures, including the world’s biggest turtle, the leatherback.

The dried krill (shrimp-like creatures of the Class Brachiopoda) that you may use as fish food form the basis of the food chain in most of the world’s oceans. Also, a number of surprisingly large creatures, including whales, manta rays and basking sharks, rely upon krill as their primary diet, consuming billions each day.

Although viewed by most as sluggish creatures, many of the world’s 70,000+ species of snails and slugs (Phylum Mollusca) are quite effective predators. Various types pry open or drill through clam shells and cone snails impale fish by shooting out barbed tongues. Certain sea slugs consume anemones and incorporate the stinging cells into their own gill tufts.

Australia’s Great Barrier Reef, the world’s largest, is 1,250 miles long. Somehow, its untold billions of individual coral animals synchronize reproduction so that the sperm and eggs of all are released into the sea at the same time.

Banded coral shrimps, Stenopus hispidus, form long-term pair bonds, and males have been observed to share food with gravid (pregnant) females. The eggs, which are glued to the females’ swimmerets (feathery structures below her abdomen), are aerated and protected by her. Upon hatching, howeRed Reef Starfishver, the young may be consumed by both parents!

Sea cucumbers make interesting if occasionally unsettling aquarium inhabitants – when disturbed, they discharge their stomachs through the anus! Amazingly, these sea star relatives can regenerate the discarded stomach.

The unique tube feet of sea stars (Phylum Echinodermata) function in locomotion, respiration and as sensory organs. Water-filled canals linking the feet can, via a series of valves, build up enough pressure to enable sea stars to pry open clam shells (try that with your hands!).

The anemone hermit crab, Parurus prideauxi, places a stinging sea anemone on its shell as protection and camouflage and re-locates it when changing shells. The anemone, in turn, gets a safe anchoring place and, perhaps, access to leftovers from the crab’s meals.

Using Invertebrates – Now and Then
Over 10,000 species of sponges (Phylum Porifora) inhabit both fresh and salt water. Several types have been collected from the Mediterranean Sea since ancient times. After drying in the sun, their fibrous structural tissue (spongin) made an excellent bath sponge.

Horseshoe crabs (Phylum Chelicerata) are among the world’s most ancient creatures and have remained relatively unchanged for over 300 million years. Closely related to spiders and not crabs at all, small specimens make interesting additions to a marine aquarium.

And, Finally…An Odd Personal Tale
Octopuses (Class Cephalopoda) are the most intelligent of the invertebrates and make fascinating aquarium subjects. They are also quite well-sighted – one I kept would, according to my grandmother, “stare” at her while she worked in the kitchen. Not wishing to upset my beloved pet, she covered its tank when preparing octopus for dinner!

Well, only a few billion more facts to go! I’ll continue next week, and periodically after that. As there are so many possibilities, I would greatly appreciate your suggestions concerning invertebrate-oriented subjects that you may wish to learn more about. Thanks, until next time, Frank.

You can learn a great deal about invertebrate biology at the web site of the Australian Museum:


Mantis Shrimp (Order: Stomatopoda) – Breaking Research and Care in Captivity

Welcome back Frank Indiviglio with another cool article.
An Introduction to Mantis Shrimp
Mantis shrimp are among the most interesting crustaceans that one might keep in a marine aquarium. Longevities in excess of 20 years are known, and many types form lifelong pair bonds. Their social interactions are incredibly complex – in some species the male hunts for the female while she guards the eggs, while in others two clutches of eggs are laid, each guarded by one parent.

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:

Great article Frank! Interesting take on what many consider a common aquarium pest.
Until next time,