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Contains articles featuring information, advice or answering questions regarding reef 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,



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:


The Use of Light Rails and Moving Aquarium Lighting in Reef Aquariums

The use of light rails, or mechanical light moving devices, has been used for many years in the horticultural industry. Now this technology is available for the aquarium hobby. By moving your light source, you can maximize the potential of an individual light fixture, by covering far more area with maximum light output vs. a stationary light source. Light energy, commonly measured in lumens, dissipates with distance from the light source. The only way to increase coverage area of a fixed light source is to move it farther away from its target area. This may cover a greater area, but will reduce the light energy that reaches the target. The other solution is to use more light fixtures, with more cost, more heat, and increased operating expense. Another problem with stationary light sources are the shadows that are created in the illuminated area, which can create unnatural growth patterns. In nature, as we all know, the sun is not in a fixed position in the sky. Areas that are shaded during parts of the day, may receive light during other times. Using a light rail mimics this natural occurrence, by changing the angle at which the light reaches its target. Areas that may not get any light with a fixed position bulb, will get light when using a moving light source.
Aquariums that require high output lighting, typically metal halide lighting, pose some problems for aquarists. These lights are very expensive to purchase, create a great deal of heat, and are expensive to operate, and replace. Using a moving light source on your reef or live plant aquarium can help solve some of these problems, you can keep your light closer to the water surface, and maximize the light energy that reaches into the aquarium. Another benefit to using a moving light system is the number of light fixtures needed to cover a given area. A six foot long aquarium can be sufficiently covered by two moving metal halide light fixtures, where it would require at least three were they stationary. Less light fixtures means less heat, less operating cost, and fewer bulbs to replace annually and more natural growth patterns.
Using light rails are not going to be practical for all applications. Smaller tanks are not practical to use these systems on, and you need to have the space to install the equipment. Applications such as “in wall” aquariums that have all the equipment hidden from view, and especially large aquariums or coral propagation systems will be able to take better advantage of what the use of light rails has to offer.
Beyond the cost and functional benefits of a light rail system, they are just plain cool to watch. The moving light source over an aquarium creates an ever changing mix of shadows and colors in your aquarium as the angles of light change on the livestock and objects in the aquarium. A moving light system is definitely a gadget geeks kind of device.
Until next blog,

News and New Research on Seahorses and Seadragons (Family Syngnathidae)

Seahorses have much to attract aquarists – armor plated and prehensile tailed, and with independently-moving eyes and wing-like fins, they can also change color as well as grow and discard filamentous appendages. And, of course, the males become “pregnant”.

My first contact with seahorses came in the mid 1960’s when my grandfather, long in awe of these unusual fishes, mail-ordered a group of dwarf seahorses, Hippocampus zosterae, from a dealer in Florida. The shipment included several males carrying eggs, and I was hooked – so much so that I wound up writing a book on seahorses.

Texas A&M researchers are now learning the male seahorse’s pouch is far more than a mere container for eggs, and are trying to discover just how such a unique organ managed to evolve. Tissue from within the pouch actually grows around the eggs and functions in a similar manner to a mammalian placenta. Through it the seahorse father is able to keep blood flowing around the eggs, and to provide them with oxygen and nutrition. Amazingly, he also makes minute adjustments to the salinity of the water within his pouch, gradually increasing it as the embryos’ needs change. By hatching time, the salinity of the pouch water matches precisely the salinity of the surrounding ocean.

The male seahorse fertilizes the eggs once they have been deposited into his pouch by the female. From that point on, the reproductive roles of the sexes are reversed. The researchers at Texas A&M are also looking into the effect this has had on mate selection and other aspects of seahorse reproductive behavior. In certain species of pipefish (close relatives of the seahorses) females have the bright coloration usually associated with male fishes, and they compete for access to the egg-incubating males. Seahorses are, as far as we know, monogamous. They form long-term pair bonds which are reinforced, in many species, with daily “greeting” rituals (the pair clasps tails, swims together, etc.), but much about how role-reversal has affected mate selection is unknown.

In other related news, the Georgia Aquarium has announced that one of its male weedy seadragons is carrying eggs, only the third time such has been recorded in a US aquarium. Weedy seadragons, and the larger and even more flamboyantly decorated leafy seadragons, are close relatives of the seahorses and pipefishes and also exhibit similar reproductive strategies.

You can read more about the Georgia Aquarium’s seadragon breeding program and see a seadragon video at:

Please also take a look at my seahorse book if you have a chance (see above) – I would greatly appreciate your feedback.

I’ll write more about keeping seahorses and their relatives in aquariums in the future. Until then, please forward your comments and questions.

Thanks, Frank.