New to Seahorses

Dear hobbyist:

Sure, your 55-gallon aquarium should have the superior height that is so important for seahorses as well as plenty of water volume to provide good stability and a comfortable margin for error. It prepared properly, it should make an exceptional seahorse setup, and I would be happy to help you get it ready for the ponies.

I’m not surprised that you have heard conflicting reports regarding the compatibility of some of your livestock with seahorses. What works well in one aquarium isn’t always successful in another tank and there are exceptions to every rule.

When discussing compatible tankmates for seahorses, it’s important to remember that one can only speak in generalities. There are no unbreakable rules, no sure things, no absolute guarantees. For instance, most hobbyists will tell you that small scooter blennies (Synchiropus ocellatus) make great tankmates for seahorses and 9 times out of 10 they’re right. But every once in a while, you will hear horror stories from hobbyists about how their scooter blenny coexisted peacefully with their seahorses for several months and then suddenly went "rouge" overnight for no apparent reason and turned on the seahorses, inflicting serious damage before it could be captured and removed.

Does that mean that we should cross scooter blennies off our list of compatible tankmates for seahorses? Nope — it just means that we must be aware that individuals within a species sometimes vary in their behavior and respond differently than you would expect, so there are exceptions to every rule. It’s fair to say that scooter blennies generally make wonderful companions for seahorses, but there’s always a small chance you might get Satan reincarnated in the form of a scooter blenny. There’s no guarantee that adorable scooter you picked out at your LFS because of his amusing antics and puppy-dog personality won’t turn out to be the blenny from hell once you release him in your seahorse setup.

Well, your tailspot blenny falls in the same category as the scooters. Like most blennies, your adult tailspot will probably do very well with seahorses and make a fine tankmate for them. But there is a slight chance that the tailspot, being an established resident of your 55-gallon aquarium, could regard any seahorses that are introduced to the tank as unwelcome intruders who are trespassing on his turf. The chances are very good that the tailspot blenny will simply ignore the seahorses, but at the same time, you must be prepared for the small chance that it will react territorially and behave aggressively towards the seahorses…

Likewise, micro-hermit crabs are generally entertaining additions to an aquarium that do a great job as scavengers and get along great with seahorses, but over the years, I’ve had a few seahorses that were confirmed crab killers. These particular ponies were persistent hermit crab predators that specialized in plucking the hermits out of their shells and attacking their soft, unprotected abdomens, and they honed their skullduggery to a fine art. They were experts at extricating the crabs and would eat only their fleshy abdomens and discard the rest. Mind you, that was only a few individuals out of a great many Hippocampines, but I could never keep hermit crabs in the same tank with those specific seahorses.

It’s the smallest hermit crabs that are at greatest risk, of course, but this behavior sometimes becomes habitual. So if my experience is any guide, crab killing could become a bad habit for the seahorse that is doing the stalking and you’ll have to watch that particular pony around hermit crabs from now one. Once they have discovered how to go about it, a seahorse may develop a taste for hermit hinders and consider them to be a regular part of its menu henceforth.

On the other hand, sometimes it’s the micro-hermits that are the troublemakers. If they are not truly a dwarf species, the hermit crabs may well grow large enough to turn the tables on the seahorses can become aggressive towards the ponies. Hermits grow rapidly, often doubling in size following a molt, and are notoriously feisty and cantankerous in nature. They may be harmless herbivores during the first part of their lives, when they are young and small, only to become aggressive carnivores with a taste for horse flesh as they grow.

Other times, the microhermits you purchased from your LFS are genuine dwarf hermit crabs that remain quite small all of their lives, yet they may be undesirable because they tend to be hard on the beneficial snails in the aquarium. Most of the time, microhermit crabs coexist perfectly well with their fellow janitors in the cleanup crew. But I’ve had more than a few tiny hermits with a taste for escargot that persecuted snails mercilessly. These cold-blooded little assassins would kill the snails in order to appropriate their shells. Once they had dined on the former occupant, they would take up residence in their victim’s cleaned-out shell! It soon became clear that these killer crabs were driven not by hunger, but by the need for a new domicile. Once I realized they were house-hunting, I found I could curb their depredations but providing an assortment of small, empty seashells for the hermits to use. Colorful Nerite shells are ideal for this.

That is the situation with the blue-leg and red-leg reef hermit crabs that are currently acting as aquarium janitors in your 55-gallon aquarium. If they are truly dwarf hermit crabs that are never going to grow much, if any, then they may do a wonderful job as scavengers cleaning up after your seahorses. But there is a significant chance that your reef hermits may reach a size where they become serious pests, if not serious threats, toward your seahorses. And there is a very good chance that the hermits may kill off the desirable snails you introduced to your aquarium to control nuisance algae, as well as a small chance that the seahorses could prey on the smallest of the hermits.

For these reasons, most seahorse keepers nowadays prefer to establish a cleanup crew consisting of an assortment of snails, supplemented by a few decorative cleaner shrimp, rather than relying on smaller crabs as their aquarium janitors and sanitation engineers. In short, to be on the safe side, you may want to remove the blue-leg and red-legged reef hermit crabs and replace them with a nice assortment of snails instead…

There are only a few species of hermit crabs that I would take a chance on in a seahorse tank. These include the following species: Dwarf Blue-leg (Clibanarius tricolor), Left-handed (Calcinus laevimanus), and above all, Scarlet Reef hermit crabs (Paguristes cadenati), which are my personal favorites. It’s very important to obtain dwarf or microhermit crabs for a seahorse tank — species that start out small and remain small even when they reach their maximum size, such as the species mentioned above.

If you’re going to have any hermits, stick with species like the above, which are known as micro hermits because they start out tiny and stay small. Avoid Anomura species of hermit crabs no matter how small they are, however, because they will kill Astraea snails to obtain their shells.

If you are uncertain which species your reef hermit crabs belong to, then it’s best to err on the side of caution and remove them before you introduce seahorses. Consider replacing them with a nice assortment of snails, such as Nassarius snails, Astrea snails, Cerith snails, Nerites, and margaritas.

The decorative cleaner shrimp that you have in your 55-gallon aquarium are another story. Most of the time they do great with seahorses, but sometimes the cleaner shrimp cause problems at feeding time and, on other occasions, the seahorses may give the colorful shrimp a hard time.

For instance, Peppermint Shrimp (Lysmata wurdemanni) and/or Scarlet Cleaner Shrimp or Skunk Cleaner Shrimp (Lysmata amboinensis) are popular additions to seahorse tanks to augment the cleanup crew and add a touch of color and activity to the tank. Peppermint shrimp (Lysmata wurdemanni) are a favorite with seahorse keepers because they eat Aiptasia rock anemones, and both the peppermints and Scarlet cleaner shrimp (Lysmata amboinensis) will perform another useful service by grooming the seahorses and cleaning them of ectoparasites. As an added bonus, they reproduce regularly in the aquarium, producing swarms of larval nauplii that the seahorses love to eat.

Yet once established in the aquarium, those beautiful red shrimp species are much more active feeders than seahorses. This is especially true of the Skunk Cleaner Shrimp (Lysmata amboinensis), also known as Scarlet Cleaner Shrimp. They’ll come flying across the tank the moment that enticing scent of frozen mysids hits the water, raiding the feeding station and snatching mysis right out of the ‘horse’s snouts. Does that mean they’re incompatible with seahorses? Heck no, you just shoo the pesky shrimp out of the way at dinnertime and target feed the seahorses, making sure each of them gets its fill.

Other seahorse keepers caution against cleaner shrimp not because the shrimp could outcompete the ponies for frozen Mysis, but because their seahorses don’t discriminate between feeder shrimp and decorative shrimp, and may be inclined to add the expensive cleaner shrimp to their dinner menu. When introducing decorative shrimp in a seahorse setup, it is important to select good-sized cleaner shrimp for this very reason. Live shrimp is the favorite food of all seahorses and, up to a certain point, they will not hesitate to attack shrimp that are too large to be eaten in one bite.

This often happens when feeding seahorses live ghost shrimp or grass shrimp, many of which are too big to be eaten intact. Seahorses are so fond of these shrimp that they often attack specimens that are far too big to swallow. In that case, they will attempt to break the back of the shrimp by snapping repeatedly at the carapace. If they are successful in severing the abdomen from the cephalothorax, the seahorses will then slurp up the tail section and head half of the shrimp separately. Or should their victim be so large it cannot even be swallowed in sections, they will snick out mouthfuls of the soft tissue exposed inside the abdomen or thorax.

At times, several seahorses will gang up on one big shrimp this way, like a pack of lions teaming up to bring down a water buffalo that’s too big for any one of them to tackle alone. Under the right circumstances, a sort of slow-motion feeding frenzy may then ensue, with the seahorses playing tug-of-war over the pieces of their prize.

Grass shrimp that are too large to be overcome by such tactics may survive to become long-term residents of the seahorse tank, coexisting with their reluctant tankmates in a sort of uneasy truce. Such die-hard shrimp provide a useful service as scavengers from then on.

We tend to think of our seahorses as gentle, nonaggressive creatures that wouldn’t harm a fly, but in reality they are surprisingly fierce predators in their own right. To small crustaceans, seahorses are the tigers of the grassblade jungle, striking without warning from ambush and devouring anything of the right size that moves.

When introduced to a seahorse setup, small cleaner shrimp face the same risks as large ghost shrimp and grass shrimp (a hungry ‘horse doesn’t distinguish between decorative shrimp that are intended as tankmates and eating shrimp that are intended as dinner). It is therefore important to select the largest possible cleaner shrimp for your seahorse tank(s). Seahorses will actively hunt small cleaner shrimp and they are quite capable of killing shrimp that are far too big to swallow whole, so the cleaners need to be large enough that they are not regarded as potential prey.

Just remember that crabs and shrimp are natural prey items that are on the menu of all large seahorses. Kealan Doyle conducted a study on seahorses in the wild in Portugal in which he did a stomach analysis of wild caught individuals, and was quite astonished to see parts of quite large crabs and shrimp in their stomach contents (Neil Garrick-Maidment, pers. com.). Of course, it’s good that Ocean Rider seahorses are such aggressive feeders, but it is inconvenient at times when they take a culinary interest in one’s hermit crab sanitation engineers.

In your case, I would say that all of the shrimp in your 55-gallon aquarium are fine and should do very well with the seahorses. Your fire shrimp (Lysmata debelius), peppermint shrimp (Lysmata wurdemanni), and skunk cleaner shrimp (Lysmata amboinensis) are all adults and should be immune from the seahorse’s predatory instincts toward shrimp. So I would encourage you to keep all of the shrimp and, if possible, to keep more than one individual of each of the shrimp. This is because the shrimp are hermaphroditic, and when two or more of the same species are kept together, they will reproduce regularly and release swarms of larval shrimp that make tasty treats for the seahorses.

Regarding the Emerald crabs, most of the time, emerald Mithrax crabs do very well with seahorses, particularly if the Emerald crab is small and there is abundant algae in the aquarium for it to eat. Will Wooten lists them as a "2" on his seahorse compatibility guide, meaning they are generally safe with seahorses with the rare exception of the occasional "rowdy" individual, and I would agree with that assessment.

Emerald Mithrax crabs are primarily herbivorous in nature and are generally shy and inoffensive in the aquarium. I would say that 90%-95% of the time, 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. 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…

The bottom line is that it’s probably safe to keep the emerald Mithrax crabs in your seahorse tank as long as there is sufficient algae for them to eat. But since your Emerald crabs are adults, if there is not algae for them to graze on in the aquarium, then it’s best to play it safe and relocate the Emerald crabs.

When it comes to starfish, your sand-sifting starfish poses no threat whatsoever to the seahorses and should do fine as long as the sand bed in your aquarium is extensive enough to sustain it. In general, as long as you avoid the large, predatory sea stars, you may certainly include small starfish and brittle stars in your cleanup crew. Any of the colorful Fromia starfish are good choices for a cleanup crew, and brittle stars are also good cleaners and very interesting in their own right.

Brittle stars are especially fascinating because they are so much more active and mobile than the usual snail-paced sea stars. They will hide under rocks or coral to get away from the bright light, but have an excellent sense of smell and will emerge from hiding the moment they detect anything edible, including frozen Mysis. When they are out and about, or tracking down their next meal from the tantalizing scent trail it leaves behind, brittle stars can’t be amazingly active and lightning fast, pulling themselves along arm over arm much more like an octopus than your ordinary, stick-in-the-mud, slowpoke sea stars. And they are excellent climbers. They pose no danger to any fishes that are too large for them to cram into their oral cavity in one piece, so there’s ordinarily no danger that they might regard your seahorses as a meal, providing you are not keeping dwarf seahorses or one of the other miniature breeds.

As far as starfish go, it’s best to avoid a large predatory species such as chocolate chip starfish and African starfish or Red Knobby Starfish (Protoreaster spp.). I would describe predatory sea stars such as these as "opportunistic omnivores," meaning that they are likely to eat any sessile or slow-moving animals that they can catch or overpower. For instance, I would not trust them with snails, clams, tunicates, soft corals and the like. Most fishes are far too fast and agile to be threatened by sea stars, but seahorses are sometimes an exception due to their sedentary lifestyle and habit of perching in one place for extended periods of time. What occasionally happens, in the confines of the aquarium, is that a predatory starfish may pin down the tail of a seahorse that was perched to the piece of coral or rock the starfish was climbing on, evert its stomach, and begin to digest that portion of the seahorse’s tail that is pinned beneath its body. That’s a real risk with large predatory species such as the beautiful Protoreaster starfish, which are surprisingly voracious and aggressive for an echinoderm.

But there are a number of colorful starfish that do well with seahorses. Any of the brightly colored Fromia or Linkia species would make good tankmates for seahorses. However, bear in mind that, like all echinoderms, starfish are very sensitive to water quality and generally will not do well in a newly established aquarium. Wait until your seahorse tank is well-established and has had a chance to mature and stabilize before you try any starfish.

Three attractive species I can recommend are the Fromia Sea Star or Marbled Sea Star (Fromia monilis), the Red Bali Starfish (Fromia milliporella), and the Red Starfish (Fromia elegans), which are all perfectly safe to keep with seahorses. They are not nearly as delicate as the Linkia species and should do well in the tank such as you’re planning that has lots of live sand and optimum water quality, and are nonaggressive starfish that feed primarily on detritus and meiofauna on live rock and sandy substrates.

But you will definitely need to find a new home for the orange/purple reef lobster (Enoplometapus sp.), even though he is always in hiding and you rarely see him. They are photophobic and shun the light, but after dark, these nocturnal lobsters are active and always on the lookout for a good meal. They are carnivores and slow-moving, bottom-dwelling fish such as seahorses are definitely on their menu. Lobsters and large crabs are natural predators of seahorses in the wild, and they do not change their nature or their feeding habits when we keep them in the aquarium. Be sure to remove the orange/purple reef lobster before you consider adding any sea horses to your 55-gallon aquarium.

In summation, here is my evaluation of the current livestock in your aquarium in terms of their compatibility with seahorses:

1. Tailspot Blenny (1 adult)

The tailspot blenny is most likely to simply ignore the seahorses and will therefore probably make an excellent tankmate for them. But there is a slight chance that the blenny will regard them as unwelcome intruders and act aggressively towards them. Keep a close eye on your blenny when you first introduce the seahorses to the aquarium and be prepared to relocate the blenny if it turns out to be one of the rare "rowdy" individuals that acts territorially.

2. Fire shrimp – l(1- adult -had him a long time, 2+ years, very shy doesn’t come out much)

The fire shrimp (Lysmata debelius) makes a great addition to a seahorse tank! Keep him and feel free to add another fire shrimp if you so desire.

3. Skunk cleaner shrimp (1 – adult)

Your skunk cleaner shrimp (Lysmata amboinensis) is another excellent tankmate for large seahorses such as Mustangs and Sunbursts (Hippocampus erectus). They normally do not hesitate to groom the seahorses just as they would in the wild. They can sometimes become a pest at dinnertime because they are active feeders that love frozen Mysis, but this is easily dealt with by feeding the other fish and inverts ahead of time and then target feeding the seahorses.

4. Peppermint shrimp (1 – adult)

Peppermint shrimp (Lysmata wurdemanni) are great tank mates for seahorses! They will rid your tank of Aiptasia rock anemones, which can be problematic for seahorses, and breed regularly when kept in pairs or small groups. Don’t hesitate to add one or more adult peppermint shrimp to your 55-gallon aquarium.

5. Emerald crabs (2)

The odds are excellent that your Emerald Mithrax crabs will do very well with your seahorses, particularly if there is abundant algae in your aquarium for them to eat. If they are large specimens and there is not enough vegetable matter in the aquarium for them to graze on a daily, keep an eye on them and be prepared to relocate them if necessary.

6. Orange/purple reef lobster (1 adult – never comes out of hiding)

Your adult reef lobster (Enoplometapus) is a seahorse predator and must go!

7. Many small blue and red legged reef hermit crabs

The hermit crabs are okay ONLY if they are all truly dwarf or micro-hermit crab species that start out small and stay small. If in doubt, relocate the hermit crabs and replace them with an assortment of snails as your cleanup crew instead.

8. Large brittle starfish

Your brittle starfish should be fine with the seahorses.

9. Sand sifting starfish

As long as your tank is big enough to sustain him, the sand-sifting starfish is completely harmless to seahorses.

Okay, that’s my opinion regarding your current aquarium residents. If you would like more tips on preparing your 55-gallon aquarium to create an ideal environment for seahorses, I recommend that you participate in the Ocean Rider seahorse training program. It’s extremely comprehensive, entirely free of charge, and will teach you everything you need to about keeping seahorses in a home aquarium. It’s a correspondence course that is conducted entirely via e-mail, so if you would like to give the training program a try, just contact me off list ([email protected]) and I will enroll you in the course as soon as we have established e-mail communication. I will then be corresponding with you personally as we go over all of the lessons to make sure that you and your 55-gallon aquarium are completely prepared for your new ponies.

Best wishes with all your fishes!

Happy Trails!
Pete Giwojna