Frantic swimming

Dear Mardean:

When algae grows on a seahorse it can become an irritant at some point, so if your aquarium is experiencing a boom of cyanobacteria or red slime algae and you notice that the little female had some of the cyano on her, my best guess is that the algae may have triggered the frantic, erratic swimming behavior, which almost looked like she was trying to scratch herself against something.

If she continues to behave normally now that you have removed the bit of cyanobacteria that was growing on her, eating as usual and swimming and purging normally again, then you probably don’t need to be overly concerned about this incident.

However, if you are indeed dealing with an outbreak of slime algae (cyanobacteria) in your seahorse tank, Mardean, you will want to eradicate it as soon as possible because it can quickly take over an entire where you want to get started. Let’s review the usual measures that are most effective in eliminating outbreaks of nuisance algae, and then we’ll discuss a product that often produces good results when all other measures futile in eliminating the slime algae.

Slime algae can be most unsightly but it is not directly harmful to seahorses. It is, however, an indicator of poor water quality since it thrives on excess nutrients in the aquarium (especially phosphates and nitrates), and of course marginal water quality can certainly be detrimental to our seahorses in the long term.

The best way to get rid of nuisance algae for good is to eliminate the excess nutrients that fuel its growth. There are a number of chemical filtration media products that will absorb phosphates from the water; any good LFS that has reef tanks and carries marine fish and invertebrates should have a number of such products from which to choose.

If you use activated carbon in your tank, it’s also very important to make sure that your carbon is phosphate free and that you change it religiously, replacing the old carbon with fresh new carbon every couple of weeks or so. (If you don’t replace the activated carbon regularly, it will begin to leach the wastes and organic compounds it has absorbed back into the aquarium water once it reaches its capacity.) Carbon is activated two ways, either with steam or with phosphoric acid. The type of carbon that is activated with phosphoric acid contains phosphates, which can likewise be leached back into the aquarium water and promote the growth of nuisance algae. So you will want to avoid that type of of activated carbon, particularly when you’re having a problem with hair algae. The carton or box that the activated carbon came in will be clearly labeled that it is "steam activated" or "phosphate free" or something to that effect if it’s a suitable brand for your aquarium. Activated carbon that is low ash and phosphate-free can help control an outbreak of hair algae if it is changed and replaced with fresh carbon diligently; however, activated carbon that is not free of phosphates or that is not changed regularly can actually contribute to a problem with nuisance algae and degrade your water quality.

In and of themselves, nitrates are relatively harmless and midrange levels are nothing to be too alarmed about. Ideally, though, we’d like to keep them under 20 ppm, and if your nitrates are running on the high side and you have a problem with red slime algae, you need to try to reduce them as much as possible. In case you haven’t already seen it, I am going to provide you with some information on nitrification and denitrification that explains where nitrates come from and then offer you some suggestions on how to reduce them.

The amount of nitrate that accumulates in your aquarium is related to how much nitrification and denitrification your system provides. Nitrification is the process by which aerobic (oxygen loving) nitrifying bacteria break down toxic ammonia to relative harmless nitrate in a series of steps. Nitrification thus ultimately causes nitrate to build up in an aquarium. Denitrification is the process by which anaerobic (oxygen hating) denitrifying bacteria then convert nitrate into completely harmless nitrogen (N2), which eventually leaves the aquarium. Denitrification thus removes nitrate from your system. This entire process is known as the nitrogen cycle.

Cycling your aquarium simply means to build up a healthy population of beneficial bacteria in your tank that can carry out the nitrogen cycle and breakdown your fishes’ waste products. Ammonia (NH3), nitrite (NO2), and nitrate (NO3) are all nitrogenous (nitrogen containing) wastes. All living aquarium animals whether they be fish or invertebrates excrete these wastes, and they are also produced by the decay of protein-containing organic matter (uneaten food, detritus, dead fish or inverts, etc.). The nitrogen cycle breaks down these wastes in a series of steps into nitrogen gas (N2) which leaves the aquarium as bubbles.

The nitrogen cycle begins with ammonia, which is highly poisonous. In the first step of the cycle, Nitrosomonas bacteria reduce ammonia to nitrite, which is also very toxic, but slightly less so. In the second step of the nitrogen cycle, Nitrobacter bacteria convert the nitrite to nitrate, which is relatively harmless but can become harmful when it accumulates in high enough levels. In the third and final step of the cycle, denitrifying bacteria then convert the nitrate into completely harmless N2, which of course bubbles out of the tank as nitrogen gas. In this way, thanks to the nitrogen cycle, dangerous wastes are converted into progressively less harmful compounds and finally removed from the aquarium altogether.

When we set up a new aquarium, and wait for it to cycle, we are simply allowing a big enough population of these different types of bacteria to build up in the biofilter to break down all of the wastes that will be produced when the aquarium is stocked. If we don’t wait long enough for the cycle to complete itself and the biofiltration to become fully established, and hastily add too many specimens to a new aquarium too soon, they will die from ammonia poisoning or nitrite toxicity. This is such a common mistake among us impatient aquarists, that when fish get sick and/or die from ammonia/ntrite poisoning, it is commonly called the "new tank syndrome."

When your aquarium has completely cycled, the ammonia levels will stay at zero because, now that your biofilter is fully established, there is a large enough population of aerobic (oxygen loving) nitrifying Nitrosomonas bacteria to reduce all of the ammonia to nitrite as fast as the ammonia is being produced. The nitrite levels will likewise stay at zero because there is also a large enough population of aerobic (oxygen loving) nitrifying Nitrobacter bacteria to convert all of the nitrite to nitrate as fast as the nitrite is being produced.

The nitrate levels ordinarily continue to build up, however, because there are simply not enough anaerobic (oxygen hating) denitrifying bacteria to convert all of the nitrate that’s being produced into nitrogen (N2). Since nitrates are being produced faster than they can be transformed to nitrogen, the excess nitrates accumulate steadily in your aquarium.

That’s perfectly normal, since the denitrifying bacteria that carry out that final step, the conversion of nitrate (NO3) to nitrogen (N2), are anaerobes that can only exist in the absence of oxygen. For our aquariums to support life, and for the fish and invertebrates to breathe and survive, our tanks must be well aerated and well circulated so that there’s plenty of dissolved oxygen in the water at all times. That means there are normally very few areas in our aquariums where anaerobic denitrifying bacteria can survive, limiting their population accordingly (which is generally good, since some anaerobes produce deadly hydrogen sulfide gas during the decay of organic matter and would poison our tanks if allowed to proliferate).

Consequently, most aquariums lack a sufficient population of anaerobic denitrifying bacteria to complete the nitrogen cycle and convert nitrate to nitrogen as fast as the nitrates are being produced. The only way to keep the nitrates from building up to harmful levels in such setups is with regular water changes and by harvesting Caulerpa or other macroalgae periodically after it has utilized nitrates for growth. Overcrowding, overfeeding, or under filtration exacerbate the problem by resulting in more nitrates being produced and more frequent water changes being required to control the nitrate levels.

Live rock helps because the oxygen-poor interior of the rock allows anaerobic denitrifying bacteria to grow and break down nitrates. A deep live sand bed (DLSB) also helps because anaerobic denitrifying bacteria can flourish and break down nitrates at a certain depth below the sand where oxygenated water no longer penetrates, but a DLSB can sometimes be difficult to set up and manage properly if you’re inexperienced with live sand. Both live rock and deep live sand beds give aquaria denitrification ability — the ability to complete the cycle and convert nitrate to harmless nitrogen. Ordinarily, about 1-2 pounds of live rock per gallon is recommended – that amount of LR will provide your aquarium with all of the biofiltration you need, as well as adequate denitrification ability. You will then keep nitrates at harmless levels by performing regular water changes, harvesting Caulerpa or other macroalgae periodically, and practicing good aquarium management.

So nitrate is simply the end product of the process of nitrification, formed during the Nitrogen Cycle by the oxidation of nitrite by aerobic bacteria. Nitrates always tend to build up in a system over time, sometimes in sneaky ways you wouldn’t expect. For example, here is an article from Thiel Aqua Tech that discusses some of the hidden ways nitrate can enter your system:

Click here: No nitrate, removal nitrate, denitrating, denitration
<<http://www.athiel.com/lib/nonitrate1.html>&gt;

One of the sneaky or hidden ways phosphates, nitrates, silicates and other undesirable compounds can enter our aquariums is through the tap water we use for water changes or topping off our tanks. If the water quality in your town is not what it should be, you may want to consider buying reverse osmosis/deinonized water (RO/DI) for your water changes. Most well-stocked pet shops that handle marine fish sell RO/DI water as a service for their customers for between 25 and 50 cents a gallon. If your LFS does not, WalMart sell RO/DI water by the gallon for around 60 cents, and you should be able to find a Wal-Mart nearby.

Natural seawater is another good option for water changes. Like RO/DI water, natural seawater can be purchased at fish stores for around $1.00 a gallon, depending on where you live. It sounds expensive, but when you consider the alternative — paying for artificial salt mix and RO/DI water and mixing your own saltwater — then natural seawater is not a bad bargain at all. It has unsurpassed water quality and seahorses thrive in it.

You should also be aware that freshly mixed saltwater can have residual levels of ammonia, but if you aerate the newly mixed saltwater for 24-48 before you perform the water changes, the ammonia will be dissipated.

Good ways to reduce nitrates in your aquarium include adding more live rock, installing a deep live sand bed (preferably in a sump), installing a protein skimmer on your tank if your not already using one, and growing and harvesting fast-growing macroalgae such as Caulerpa.

Protein skimmers help reduce nitrates by removing dissolved organics from the water before they can enter the nitrogen cycle. The majority of the undesirable metabolites, organic wastes and excess nutrients that accumulate in our aquariums and degrade water quality are "surface-active," meaning they are attracted to and collect near the surface of a gas-liquid interface. Skimmers take advantage of this fact by using a column of very fine air bubbles mixed with aquarium water to trap dissolved organics and remove them from our systems. This air-water mixture is lighter than the surrounding aquarium and rises up the column of the skimmer until the foam eventually spills into a special collection cup atop the skimmer, which can be removed and emptied as needed. Proteins and other organic molecules, waste products, uneaten food and excess nutrients, and a host of other undesirable compounds stick to the surface of the bubbles and are carried away along with the foam and removed from the aquarium. As a result of this process, these purification devices are typically known as foam separators, foam fractionators, air-strippers, or simply protein skimmers.

In my experience, nothing improves water quality like a good protein skimmer. They provides many benefits for a seahorse setup, including efficient nutrient export, reducing the effective bioload, and increasing both the Redox potential and dissolved oxygen levels in the water. They do a tremendous job of removing excess organics from the aquarium, including phenols, albumin, dissolved organic acids, and chromophoric (color causing) compounds. Their ability to remove dissolved wastes BEFORE they have a chance to break down and degrade water quality makes them indispensable for controlling nuisance algae. A good protein skimmer is an invaluable piece of equipment for keeping your nitrates low and your water quality high when feeding a whole herd of these sloppy eaters in a closed-system aquarium.

I also like the use of macroalgaes for controlling nitrate and nuisance algae. Macroalgae use nitrate for growth just like plant fertilizer and pruning the macros regularly is a good way to export nitrate from your system. However, if the macros die in your system, they’ll release the nitrate they’ve consumed back into the aquarium. Fast-growing Caulerpa needs to be pruned properly to prevent vegetative events and avoid this from happening, as discussed below:

Macroalgae act as an excellent form of natural filtration, reducing the available levels of phosphates and nitrites/nitrates. Be sure to prune and trim back the fast-growing Caulerpa regularly; when you remove the clippings, you’re exporting phosphates, nitrates and other nutrients from the tank, thereby helping to maintain good water quality, and pruning the runners helps keep it from going sexual.

When pruning or trimming back macroalgae, take care not to actually cut it. Remember, you’re not pruning hedges or trimming trees — the idea is to carefully pull up and remove continuous, unbroken fronds. Simply thin out the colony of excess strands, gently plucking up convenient fronds that can be readily removed intact. A little breakage is fine, but cutting or breaking too many strands will result in leaching undesirable substances into the aquarium water as the Caulerpa lifeblood drains away. Too much cutting or breaking can thus sap the colony’s strength and cause die offs or trigger the dreaded vegetative events that judicious pruning otherwise prevents.

Another product I like for removing excess ammonia, nitrite, and nitrate is the Poly-Filter Pad (by Poly-Bio-Marine) Here is a product review on Poly Filters that touches on some good ways to use them:

Click here: Saltwater Aquariums Product Review – Poly-Bio-Marine Inc. – Poly Filter Pad
<<http://saltaquarium.about.com/cs/filtration/l/blprbiomarinpad>&gt;.

Finally, commercially made denitrators (special filters housing a large population of anaerobic denitrifying bacteria) are also available. They do a tremendous job of controlling nitrates but are rather expensive and tend to be high maintenance, often requiring regular "feeding" and carefully controlled flow rates to operate properly.

The hobbyist should also be aware that dead spots and low flow areas, as well as low pH levels, favor the growth of nuisance algae rather than coralline or macroalgae and marine plants. Eliminating dead spots and stabilizing your pH at 8.2-8.4 can therefore help tip the balance back in the favor of macros and coralline algae, and help prevent problems with nuisance algae.

One simple measure that can thus make a big difference is to try positioning one or more small powerheads so that they increase the circulation in the area where the nuisance algae tends to grow. Better water movement and higher oxygen levels will naturally tend to minimize the growth of slime algae and hair algae in these problem areas.

If your pH is running on the low side, that may also be contributing to your problem with nuisance algae. Correcting the pH and maintaining the alkalinity in your aquarium at the proper level will help you get the cyanobacteria and nuisance algae back under control.

In summary, Mardean, some of the measures that will help control nitrates and phosphates (and excess nutrients in general), or which can otherwise help control nuisance algae in the aquarium are the following:

1) Make sure your protein skimmer is working correctly. A protein skimmer works 24 hours a day to remove excess waste and nutrients from a tank. If the venturi is clogged on a venturi skimmer or there is another problem with other skimmer designs, waste will not be exported from your tank and algae will take advantage of the waste.

2) Perform regular water changes. Regular water changes will decrease the level of wastes and nutrients in the water. But the water changes won’t do much good if your tap water itself contains phosphates and amines. Depending on how high the nitrate levels become, increasingthe proportion of water that you change each time may be necessary to help reduce those nitrates. There is an article about nitrate reduction at <<http://www.about.com/>&gt; in the saltwater section that really explains water changes (gives you the math), on actually how little you are reducing nitrates with small water changes when you have high nitrates.

3) Make sure makeup water is pure. Phosphates and nitrates often found in tap water. Phosphate and nitrate test kits will show if your tap water is contributing to your algae problem. If phosphate and nitrate levels are more than 0 ppm (some tap water measures out at over 50 ppm nitrate), filter the water through a RO/DI unit before using it as makeup freshwater or as source water for saltwater changes, or purchase RO water from a vendor.

4) Add additional detritivores to your cleanup crew. If excess food isn’t eaten, it will decay and add to the nutrients and waste in the tank. More microhermit crabs, Nassarius snails and cleaner shrimp will help ferret out any uneaten Mysis before it breaks down and enters the nitrogen cycle to eventually end up as excess nitrate.

So if you’re having a problem with nuisance algae, consider bolstering your cleanup crew with additional snails and/or micro-hermit crabs that eat slime algae and other types of nuisance algae. Astrea snails, red foot moon snails, and Scarlet reef hermit crabs (Paguristes cadenati) all fit the bill and would be good additions in that regard.

Garf (<http://www.garf.org/redslime.html&gt;) offers a Reef Janitors package with the hermits (chibanarius or clibanarious digueti, mexican dwarf hermit) and the snail (Cerithium strercusmuscarum), which are said to do a good job of cleaning up red slime algae.

Introduced as soon as possible to a new aquarium, as soon as the ammonia and nitrite levels are safe, Astrea snails effectively limit the development of all microalgae. In other words, they are good at eating diatoms, but will consume red slime and green hair algae as well. The Scarlet Reef Hermit Crab (Paguristes cadenati) is a colorful micro-hermit that’s a harmless herbivore. So cannibalism isn’t a concern at all for these fellows, nor are they likely to develop a taste for escargot. As hermits go, most of the time the Scarlet Reefs are perfect little gentleman and attractive to boot. I even use them in my dwarf seahorse tanks. Best of all, they eat all kinds of algae, including nuisance algae such as red, green and brown slimes, as well as green hair algae.

5) Introduce macroalgae to consume excess nutrients and nitrates. If regular pruning is done, fast-growing Caulerpa will maintain its color and high growth rates without going sexual. Better yet, an algal filter or "algae scrubber" can be established in a sump or refugium.

6) Chemical controls. Phosphate absorbers can remove excess phosphates, and Poly Filter pads can help absorb excess nitrates, changing color as they do so, which helps indicate= when the Poly Filter needs to be changed. Low ash activated carbon that is free of phosphates will also help remove such nutrients if it is change religiously and replaced with new carbon.

7) Controlled addition of food to tank. Don’t broadcast feed, scattering Mysis throughout the tank. Instead, target feed your seahorses or use a feeding station. Don’t overfeed, cleanup leftovers promptly, and observe fast days religiously.

8) Eliminate dead spots and increase the water flow in areas where the nuisance algae tends to grow.

9) Maintain the pH and total alkalinity of the aquarium in the proper range. Monitor alkalinity or carbonate hardness and the calcium levels in the tank as well as the pH.

10) Replace your aquarium lamps regularly to assure that the spectrum of light they put out favors the growth of coralline algae and macroalgae. (Over time, as bulbs age, they begin to put out light shifted more towards the red-end of the spectrum, which encourages the growth of hair algae and nuisance algae.)

For more information, check out the following three online articles which are loaded with additional tips and suggestions for controlling outbreaks of nuisance algae:

http://www.syngnathid.org/articles/greenHairAlgae.html

<http://www.seahorse.org/library/articles/ProblemAlgae.shtml&gt;

Click here: CyanoControlFAQs
<http://www.wetwebmedia.com/cyanocontrolfaqs.htm&gt;

Click here: GreenAlgContFAQs
<http://www.wetwebmedia.com/greenalgcontfaqs.htm&gt;

Cyanobacteria or red slime algae can be very stubborn and difficult to eradicate in some cases, Mardean, and if the slime algae fails to respond to such measures in your case, there is one other product that can usually save the day. However, you must use it with caution, as discussed below:

If all else fails, stubborn cases of red slime algae (i.e., cyanobacteria) can be eradicated using a product called ChemiClean. It is designed specifically to get rid of Cyanobacteria and slime algae in the aquarium, and often works wonders when all other efforts to get rid of the red slime algae have failed. ChemiClean is not an antibiotic and it is safe to use in reef tanks; it is said to be safe for corals, invertebrates and fishes in general.

So one option would be to treat your aquarium with ChemiClean while the seahorses are in it. I know some hobbyists who have done so with excellent results and no harm whatsoever to their seahorse (Leslie Leto, per. com.).

However, I hesitate to suggest this product to seahorse keepers except as a last resort, Mardean, due to the potential risk of asphyxiation. Chemi-Clean evidently acts by oxidizing the organic "sludge and settlements" that accumulate in aquaria, in a process which apparently consumes oxygen from the water in much the same way as formalin does. That is why the online instructions specify that you add an airstone, preferably one with a wooden air diffuser, to provide efficient aeration and oxygenation of the aquarium when you use the product.

You must turn off your protein skimmer to use this product, which in itself reduces the aeration and oxygenation in the aquarium, and when this is combined with the oxidizing action of the Chemi Clean, which further reduces the dissolved oxygen level in the aquarium, it can create a dangerous condition for your seahorses due to the risk of asphyxiation. Seahorse setups in particular are susceptible to such problems because hobbyists are so conscious of their seahorses’ limited swimming ability that they tend to leave their aquariums undercirculated. Poor circulation and inadequate surface agitation can lead to inefficient oxygenation and insufficient offgassing of carbon dioxide.

Seahorses are more vulnerable to low O2/high CO2 levels than most fishes because of their primitive gills. Unlike most teleost (bony) fishes, which have their gills arranged in sheaves like the pages of a book, seahorses have rudimentary gill arches with small powder-puff type gill filaments. Their gills are described as "tufted" because they appear to be hemispherical clumps of tissue on stems. Their unique, lobed gill filaments (lophobranchs) are arranged in grape-like clusters and have fewer lamellae than other teleost fishes, making them a little less efficient.

So if you want to try ChemiClean while your seahorses are in the tank, be sure to add a least one airstone for additional aeration and oxygenation and observe all of the precautions in the instructions. Once you obtain the ChemiClean, perform a large water change and remove as much of the red slime algae as you can before you add the first dose. Remove your chemical filtration media but keep all your filters running so they roil the surface of the water and provide adequate surface agitation to promote oxygenation and facilitate efficient gas exchange at the air/water interface.

Then after you use the ChemiClean according to instructions and have performed the requisite water change, reinstall fresh activated carbon, and start your protein skimmer operating again. Please read all of the information at the following web site before you make a decision on whether or not to use the ChemiClean, Mardean:

Click here: Reef Show – CYANO BACTERIA: red-slime algae? Cause and Relief
http://reefshow.com/html/modules.php?name=News&file=article&sid=109

Best of luck getting rid of that unsightly slime algae, Mardean!

Respectfully,
Pete Giwojna

Dear Mardean:

I’m very sorry to hear that you lost the female after all. All my condolences on your loss, Mardean!

Clearly something more was bothering her then the irritation from algae growing on her, but it’s very difficult to determine what was wrong with so little to go on. Sunbursts are a bit smaller than Mustangs on average, but I would not have expected your female to be half the size of the others, and if she was simply a younger seahorse, then one would expect to see a faster growth rate from her as compared to the more mature seahorses. But that’s not what you observed, which does suggest that something may have been bothering her for quite some time now.

Intestinal flagellates may be one possibility, Mardean. When a seahorse is a good eater yet fails to grow as expected or loses condition despite a good appetite, that can be an indication of a heavy infestation with intestinal flagellates, as discussed below:

Intestinal Flagellates

Intestinal flagellates are microscopic organisms that move by propelling themselves with long tail-like flagella (Kaptur, 2004). Such flagellates are ubiquitous and can be found in both the gastrointestinal and reproductive tracts of their hosts. In low numbers they do not present a problem, but they multiply by binary fission, an efficient means of mass infestation when conditions favor them (such as when a seahorse has been weakened by chronic stress), Kaptur, 2004. When they get out of control, these parasites interfere with the seahorse’s normal digestive processes such as vitamin absorption, and it has difficulty obtaining adequate nourishment even though it may be eating well and feeding heavily (Kaptur, 2004). Suspect intestinal parasites are a work when a good eater gradually wastes away despite its hearty appetite (Giwojna, Dec. 2003). Their presence can be confirmed by examining a fecal sample under a microscope, but they can be easily diagnosed according to the more readily observed signs described below (Kaptur, 2004).

The symptoms to look for are a seahorse that’s losing weight or not holding its own weightwise even though it feeds well, or alternatively, a lack of appetite accompanied by white stringy feces (Kaptur, 2004). When a seahorse stops eating aggressively and begins producing white, stringy feces instead of fecal pellets, that’s a clear indication that it’s suffering from intestinal flagellates (Kaptur, 2004). Treat the affected seahorse(s) with metronidazole at the first sign of either condition (Giwojna, Dec. 2003).

Metronidazole is an antibiotic with antiprotozoal properties that is very effective in eradicating internal parasites in general and intestinal flagellates in particular (Kaptur, 2004). It is ideal for this because it is rapidly absorbed from the GI tract, has anti-inflammatory effects in the bowel, and was designed specifically to treat protozoal infections and anaerobic bacterial infections by disrupting their DNA (Kaptur, 2004).

When administered properly, metronidazole is wonderfully effective at eliminating intestinal parasites, and there should be signs of improvement within 3 days of treatment (Kaptur, 2004). The seahorse’s appetite should pick up, and as it does, those characteristic white stringy feces will return to normal (Giwojna, Dec. 2003).

Intestinal parasites are typically transferred from their host to uninfected fishes by fecal exposure, and good tank management and hygiene can therefore go a long way towards limiting their spread (Giwojna, Dec. 2003). You don’t want seahorses eating frozen Mysis that may have become contaminated from laying on a dirty substrate (Giwojna, Dec. 2003). Using a feeding station can help prevent this as can vacuuming the substrate regularly.

Fortunately, intestinal flagellates have virtually no ability to survive outside their host’s body (Giwojna, Dec. 2003). If you are diligent about aquarium maintenance and keeping the substrate clean, Mardean, the parasites should be easily eliminated from your system and chances are good the rest of your herd will remain unaffected (Giwojna, Dec. 2003).

It’s difficult to determine if your Emerald Mithrax played a role in the female’s demise or if the crab was simply scavenging the carcass of the seahorse after it had died. Emerald Mithrax crabs are primarily herbivorous in nature and are generally shy and inoffensive in the aquarium. I would say that 9 times out of 10, Emerald Mithrax make fine tankmates for seahorses and cause no problems at all. It’s just those rare exceptions and uncommonly cantankerous individuals you must be wary of, Mardean. Even the gentle Emerald crabs can very occasionally become problematic if they are not getting enough vegetable matter in their diet, in which case they may become opportunistic omnivores and are no longer averse to adding a little meat to their diet should they get hungry enough.

Remember, crabs and crustaceans in general are opportunistic predators that are liable to attack anything they can overpower. They may be entirely peaceful and inoffensive when they are small, but even a small crab can cause a lot of trouble as it grows. They may double in size following a molt (i.e., ecdysis) so they grow surprisingly fast, and even a tiny crab that’s completely docile at first can grow large enough to turn predatory almost literally overnight if it’s a species that reaches a respectable size. One day it’s a miniature crab that’s cute and entertaining in its own bumbling sort of way, and the next day following a successful molt, it can become a dangerous bully that regards its tankmates with a culinary eye.

Keep in mind that there are always exceptions to every rule, and large crustaceans are never completely trustworthy. Even the most harmless and seemingly inoffensive crabs can cause trouble under certain circumstances. For example, not long ago I heard from a hobbyist that had been keeping a decorator crab in his seahorse tank. All went well at first and there were no problems of any kind for months until, for no apparent reason, the crab suddenly began to quite deliberately amputate portions of the seahorses’ tails. It was not attacking the seahorses as prey or attempting to eat its mutilated victims, it was merely methodically harvesting portions of their anatomy with which to adorn itself! It was simply doing what all decorator crabs do — snipping off and gathering bits and pieces of its immediate environment to attach to itself as a form of natural camouflage. It just goes to show, with crabs you can never be sure how things are going to work out…

So it’s hard to say whether your Emerald Mithrax helped hasten the demise of your female or if it was merely fulfilling its role as a scavenger, Mardean. If the Emerald crab had been acting aggressively toward the little female under the cover of darkness from time to time, it’s possible that this behavior was stressful to the female, which in turn allowed intestinal flagellates to gain the upper hand and become too numerous for her welfare, so it could’ve been a combination of things that weakened her.

At any rate, those are the only things that occur to me at this time, Mardean.

Best of luck with the rest of your seahorses! Let us know right away if you notice any other symptoms or signs of a problem.

Respectfully,
Pete Giwojna