With the only possible exception being Clownfish, there are perhaps no more recognized species of marine fish worldwide, even among non-hobbyists, than those in the genus Hippocampus. Of course, non-hobbyists (and even most hobbyists) do not, however, know them by this name. These fish are used in a wide assortment of industries outside the marine aquarium trade. They are harvested and sold in the Asian market for medicinal purposes. Although the American market doesn't rely on such ancient pharmaceutical remedies, you will be hard pressed not to find dried and lifeless carcasses used as curios, sitting on shelves alongside starfishes and sand dollars. Undoubtedly, their unique and uncharacteristic morphology has endeared them to the hearts of people worldwide. It should not be any surprise, therefore, to learn that the same intrigue exists within the aquarium trade. Most hobbyists who have been in the marine aquarium hobby for several years and have experienced at least moderate degrees of success, have almost certainly given thought to keeping Hippocampus species. Their husbandry needs cannot be successfully met, however, without gaining an education about their requirements. I would therefore like to use the November Fish Tales column to discuss the strange looking fishes in the genus Hippocampus, affectionately known as the Seahorses.

Meet the Family

All members of the Syngnathid family, namely the seahorses, pipefish, pipehorses, and sea dragons, possess an elongated semi-flexible body with armored, bony plates. They have no scales, stomach, or even teeth. Gill openings are usually reduced to small round pores, and the head is generally long and tubular. The jaws are fused, resulting in a structure without a hinge to open and close. Hard rays are not present within the fins which are comprised entirely of the ever-so flexible soft rays. Most species will have a dorsal fin and pectoral fins, while some species lack an anal fin entirely. Of the species that do have an anal fin, the fin is generally not well-developed and doesn't seem efficient enough to help with the locomotion of the fish. Some species may have caudal fins, while yet other species lack caudal fins entirely. Ventral and second dorsal fins are absent in all Syngnathids. Another factoid worth mentioning about Syngnathids is their reproductive habit: the males are the ones that become pregnant! In all species the male carries the eggs during the incubation period (more on this shortly).

Seahorses have been placed into the family Syngnathidae with their closely related cousins the Pipefish, Pipehorses, and the Sea Dragons. Together they comprise the four subfamilies of Syngnathidae. Rarely seen in the home aquarium, Solegnathinae, the first subfamily, contains both the Seadragons and the Pipehorses. More common to the home aquarium is Syngnathinae, consisting mostly of Pipefishes but also including some species awaiting further research. The free-swimming pipefish are all placed in the subfamily Doryrhamphinae. Finally, Seahorses are all grouped into the last subfamily, Hippocampinae.

Hippocampinae consists of ten species assigned to four genera - Amphelikturus, Acentronura, Idiotropiscis, and Hippocampus. The seahorses belong in Hippocampus and the Pygmy Seahorses are placed in the three previous genera. As the name may suggest, all of these "pygmy" species are extremely small, most less than two inches tall. An easy test that distinguishes them from seahorses is that the pygmy seahorses swim horizontally, whereas the seahorses of Hippocampus are vertical swimmers.

In 1810 Rafinesque was the first to formally describe the genus Hippocampus. In the same year H. erectus, the first species was described by Perry. Almost 200 years later ichthyologists continue to add seahorse species to the genus Hippocampus without naming any additional genera, subgenera, or even complexes. Despite agreeing on a single genus, it doesn't seem anyone can agree on the number of species. As early as 1958 Whitley and Allan suggested the total number of species exceeded over 100. Eschmeyer (1998) recognized 112 species. However, Lourie in Lourie, et al. (1999) formally recognized only 32 species. Chances are, however, this number is considerably low given the reasons I'll discuss shortly. Only one year later Kuiter (2000, 2001) estimated the number to be closer to 60+ species, but formally recognized only 54 species, and named only 44. As his is the most current work revision, I will follow Kuiter (2000) with the following list of species. Furthermore, I have included additions to the genus which include, H. denise, provided by Lourie and Randall (2003), nine species from Kuiter (2001), H. queenslandicus from Horne (2001), and H. colemani Kuiter (2003). A complete revision is currently underway by Lourie.

Two additional species have been photographed and observed by divers, but they have yet to be scientifically recorded and named. It is likely these species will be fully documented in the next revision by Lourie. Each species will likely have a maximum recorded size smaller than Hippocampus denise, currently the smallest formally documented Hippocampus.

Contributing to the confusion of naming species is the lack of the typical osteological features that ichthyologists classically use for discerning differences between individuals. Instead of charting the dentition of the jaw structure, the length of snout is considered. Whereas the color of species is important for many fish, the coronet on the head is more likely to tell the difference between seahorses. The number of dorsal and anal rays is equally important in discerning seahorses, just as they are in any other fish, but additionally, ichthyologists will also use the number of rings on the trunk or tail. Although spine development - or the lack thereof - has often been used to help distinguish species, it has become known lately that some species are smooth-sided as juveniles, yet grow thorny sides as they age. Likewise, thorny juveniles sometimes grow into smooth-sided adults.

Estimates of the total number of species actually in this genus have been made since the early 1800's. Canvassers such as Whitley and Allan (1958) have taken the stance that many seahorse species are endemic and localized by naming over 100 species. This makes sense considering seahorses do not have a pelagic stage and generally remain localized. In contrast, Lourie, et al. (1999) obviously disregards the localization of the species by naming only 32 species worldwide. As may later be confirmed through extensive research; however, the number likely lies somewhere in the middle as suggested by Kuiter (2000) because relative prominence of species-complexes is one aspect that has not yet been fully investigated. Species-complexes can develop when climatic changes affect localized individuals that are unable to migrate to areas of optimal water quality resulting in slight morphological changes. The waters surrounding Australia represent a textbook case of just such an instance with their 17 different demersal bioregions (CSIRO, 1999). Populations on the east or west coast were able to move latitudinally as the water temperature changed, but species on the south coast were unable to make the needed adjustments, thereby allowing for speciation over time (Kuiter, 2000). Only when a close look at species-complexes is undertaken will this genus begin to be fully understood.

In the Wild

All tropical and sub-tropical seas of the world house seahorses. A few species are known to extend into the Australian and New Zealand temperate seas, while no species are found in cold water. With that said, the warmer tropical seas show a larger number of species than do the cooler waters of the north Atlantic or southern Australia. One species, Hippocampus capensis, has been observed even in estuaries of varying salinity.

Seahorses, like all Syngnathids, are secretive fish and are highly localized and restricted in their distribution. They are more likely found in bays and lagoons than on the fore-reef. In locales where a seahorse species occurs in shallow water over a rubble or rock sea floor, a second, different species likely lives nearby in slightly deeper water over a soft mud bottom. Seahorses have been viewed, photographed, or collected in waters only several feet deep and conversely at least one species has been trawled from depths beyond 200 feet (H. spinosissimus). Additionally, with only two specimens of H. spinosissimus known, it is the rarest species of the genus. On the opposite end of the spectrum is H. histrix, which is known from Japan to Bali, most parts of Indonesia and the Red Sea, and onto Papua, New Guinea and even into Hawaiian waters, making it the species with the widest distribution. In light of their overall localization and reproduction mode, this wide distribution is rather remarkable. In fact, it is so remarkable it has led some researchers (Kuiter, 1999) to consider the possibility that H. histrix juveniles may have a pelagic stage. Alternatively, further research on this genus may negate some of the localities, as there may have been misidentified species listed, thereby reducing its geographical distribution. At least one species, H. bargibanti, is pelagic for a portion of its life cycle. It settles onto various gorgonian corals and shortly thereafter will adapt the coloration and general shape of the coral (Gomon, 1997).

Fry Photos

Top left: A captive-bred male H. erectus delivering fry. Top center: A four week old H. barbouri. Top right: Seven week old H. barbouri. Bottom left: Two day old H. barbouri fry. Bottom center: H. barbouri fry at one day old. Bottom right: H. barbouri fry at nine days. All images courtesy of Leslie Leddo.

More often than not, finding one seahorse will mean that a second seahorse of the opposite sex is nearby. Their pair-bonds are almost always maintained, as seahorses are a rarity among marine fishes in that they maintain monogamous bonds. The pair will greet each other every morning as the sun begins to wake up the reef. After interacting for several minutes - longer during the non-spawning season or periods during which the male is not carrying eggs - the pair will go their separate ways. It is speculated that these regular meetings facilitate and synchronize the reproductive systems of each individual.

Speaking of reproduction, this is most definitely worthy of further discussion. Seahorses have a unique mating and reproductive strategy, which only adds to their mystique. Unlike many marine animals which have little or no interaction with the eggs once spawning has commenced, seahorses will not only offer protection to the eggs during their maturation process, but it is in fact the male who cares for the unhatched eggs. Herein lies the noteworthy part - the male cares for the eggs by carrying them in a small pouch, referred to as the brood pouch. In most Hippocampus species this pouch lies on the ventral side of the tail - what most people would refer to as the front of the fish - roughly around the stomach area. This pouch, which will develop in males usually between the age of four to six months, is the easiest way to distinguish males from females. For H. minotaur, however, the pouch is located on the tail, whereas H. denise and H. bargibanti have no pouch but instead use the entire trunk. These egg depositories will incubate the fertilized eggs until they hatch and the miniature seahorses are fully developed. For an idea of how unusual it is for males to care for their young, of the 422 bony fish families only 89 offer parental care while 36 exhibit paternal care (Blumer, 1979).

Of course, long before the diminutive replicas can get to this point, the parents must engage in reproductive behaviors. Like anything else associated with seahorses, the act of reproduction is noteworthy. Courtship begins up to three days prior to consummation. Erect fins and color changes help convince the female of the upcoming egg transfer. Two days prior to impregnating the male, the female will begin to show signs of pregnancy herself as her abdomen begins to swell. Just prior to mating, in an act to show that he's ready and willing, the male will begin to flex his tail up and down. No, he is not showing off his bulging muscles for the lovely lady, but instead he is pumping water in and out of his brood pouch, obviously preparing it for the ensuing pregnancy. Once the female accepts the male's advances, the pair interweave their bodies, rise from the sea floor, and the female deposits the eggs into the male's brood pouch using her ovipositor. The male will then fertilize the eggs internally. Similar to the lining of a mammal's womb, the eggs embed into the wall lining of the pouch and are then covered by a placental fluid which bathes the eggs in nutrition, oxygen, and a constant osmotic environment. Within 21 days or less, depending on the particular species and water conditions, the male will eject his newborn offspring.

Defenses from natural predators are few and far between for juveniles and adults alike. Depending on how you view it, they are both sorely lacking and exceptionally advanced. The bony plates, which line their exterior as body armor, invoke images of a knight from centuries ago. However, this offers minimal protection from predators that are likely to swallow them whole. So it is possible to view them as needing a 21st century upgrade. In contrast, it is also possible to think seahorses have been ahead of their time for centuries. With their ability to change color and color pattern or grow skin filaments to match their surroundings, seahorses are able to pull off a camouflage that a Navy SEAL would envy. To get an idea of how well this camouflage works, take a look at this Windows media file showing a Hippocampus bargibanti in its natural habitat.

A couple of morphological features are well worth discussing. The tail of seahorses is unique in that is fully prehensile. As the word implies this tail is exceptionally proficient at grasping onto blades of sea grass, gorgonian branches, or any number of other holdfasts that are found in the marine environment. Rarely will they release their grip on their favorite holdfast, which often pulls double duty as a form of camouflage. Another interesting feature is the Chameleon-like eyes that can rotate independently of each other. One eye can clearly be focusing on you while the other intricately searches the growths of algae - always providing a sense of amusement to those observing it for their first time. A tube-like mouth has adapted to sucking up prey like a Hoover vacuum due to their complete lack of teeth. Finally, the stomach of seahorses is absent; they instead have a highly inefficient digestive tract necessitating consumption of large quantities of food to mitigate the effects of their poor utilization of the captured prey's nutritional value. The food items consist of most any live items which can be siphoned through their mouths. More often than not this includes both amphipods and copepods.

In the Home Aquarium

Perhaps the biggest factor facilitating success with seahorses in the home aquarium is placing them into the proper aquarium with suitable tankmates. Placing the seahorse into a reef aquarium display containing active fishes or stinging corals will most likely be highly unsuccessful. Seahorses should be given a tank unto themselves free of aggressive fish, corals, or mobile invertebrates. Anemones and large-polyped stony (LPS) corals should be entirely avoided, as the seahorses will be stung and injured if they come into contact with the powerful stinging cells found within the tentacles. These wounds could possibly be fatal, and in some cases the seahorses may even be consumed by the anemones. Large crabs will actively hunt seahorses and, if given the chance, will capture and consume them. Due diligence is required to remove any hitchhiker crabs prior to declaring the aquarium suitable for seahorses. I offer a general compatibility chart below only because I realize a percentage of seahorse enthusiasts will be unable to resist the urge of adding at least a couple of other species. However, allow me to strongly recommend a species-dedicated aquarium.

Compatibility chart for Hippocampus species:

Fish	Will Co-Exist	May Co-Exist	Will Not Co-Exist	Notes
Angels, Dwarf			X	Will be out-competed for food.
Angels, Large			X	Will be out-competed for food.
Anthias			X	Will be out-competed for food.
Assessors	X			An excellent choice.
Basses			X	Will be out-competed for food.
Batfish			X	Will be out-competed for food.
Blennies	X			An excellent choice.
Boxfishes		X		Food competitor - direct feeding will likely be required.
Butterflies			X	Will be out-competed for food.
Cardinals		X		Food competitor - direct feeding will likely be required.
Catfish			X	Will be out-competed for food.
Comet	X			An excellent choice.
Cowfish		X		Food competitor - direct feeding will likely be required.
Damsels			X	Will be out-competed for food.
Dottybacks			X	Will be out-competed for food.
Dragonets	X			Assuming enough food is present for all.
Drums			X	Will attempt to consume seahorses.
Eels			X	Will attempt to consume seahorses.
Filefish		X		Food competitor - direct feeding will likely be required.
Frogfish			X	Will attempt to consume seahorses.
Goatfish			X	Will attempt to consume seahorses.
Gobies		X		Food competitor - direct feeding will likely be required.
Grammas		X		Food competitor - direct feeding will likely be required.
Groupers			X	Will attempt to consume seahorses.
Hamlets			X	Will attempt to consume seahorses.
Hawkfish		X		May harass or attack seahorses.
Jawfish		X		Food competitor - direct feeding will likely be required.
Lionfish			X	Will attempt to consume seahorses.
Parrotfish			X	Overall size; aggressive feeding and swimming habits.
Pineapple Fish		X		Food competitor - direct feeding will likely be required.
Pipefish		X		Seahorses may harass some pipefish by trying to hitch a free ride.
Puffers			X	May harass or attack seahorses.
Rabbitfish			X	Food competitor - direct feeding will likely be required.
Sand Perches			X	Will attempt to consume seahorses.
Scorpionfish			X	Will attempt to consume seahorses.
Seahorses	X			An excellent choice.
Snappers			X	Will attempt to consume seahorses.
Soapfishes			X	Will attempt to consume seahorses.
Soldierfish			X	Will attempt to consume seahorses.
Spinecheeks			X	Will attempt to consume seahorses.
Squirrelfish			X	Will attempt to consume seahorses.
Surgeonfish			X	Will be out-competed for food.
Sweetlips			X	Will attempt to consume seahorses.
Tilefish			X	Will be out-competed for food.
Toadfish			X	Will attempt to consume seahorses.
Triggerfish			X	Will harass or attack seahorses.
Waspfish			X	Will attempt to consume seahorses.
Wrasses			X	Will be out-competed for food.

Note: While many of the fish listed are good tank mates for Hippocampus species, you should research each fish individually before adding it to your aquarium. Some of the mentioned fish are better left in the ocean or for advanced aquarists.

As you have probably gathered from above, the largest hurdle to housing seahorses with other tankmates is getting enough food to the seahorses. Most tankmates do not afford them the luxury of time that seahorses require. They do not actively hunt their food. Prey items must swim within striking distance before any effort is put forth to capture it. Therein lies the reason that seahorses are unable to co-exist with most other fish.

Of course, the aquarium must be prepped before considering tankmates. Densely packed live rock and rubble piles are fantastic for encouraging a healthy and abundant population of copepods and amphipods. A dense growth of various species of macroalgae is another consideration for optimizing the "pod growing sanctuaries." Of course, another route to achieve the same objective is to have a functional refugium. The more natural foods the aquarium can produce, the better off the 'horses will be. The aquarium's viewing area should be open and uncluttered while water flow should be slow, but steady. Seahorses are not nimble and do not easily navigate around aquariums with abundant circulation. Providing plenty of anchoring sites in conjunction with a low water current is key to making their aquarium life easier. Suitable holdfasts would include gorgonians and sea fans, Halimeda algae, stick sponges, and just about anything the seahorses can wrap their tails around.

Allowing this aquarium several months to settle in and establish significant populations of microfauna is another way to ensure the aquarium is as suitable as possible prior to introduction. Even with an effective refugium and healthy populations of in-tank microfauna, food supplementation will be required. Hatching brine shrimp, mosquito larvae, or even daphnia at home can prove to be successful means of food supplementation. These live foods can be especially successful for getting newly acquired animals eating and settled in. Perhaps the easiest foods to feed are prepared foods of thawed mysid shrimp. Most seahorses will readily accept this food, and as an added bonus, it is highly nutritious. Most important, due to the lack of a stomach and inefficient intestines, the hobbyist must be prepared to provide large amounts of these foods. It would be wise to consider that three feedings per day are the minimum necessary.

Regarding water parameters, as with any saltwater fish, the hobbyist should strive for tank conditions as near to natural saltwater conditions (NSW) as possible. Seahorses, however, seem to be slightly forgiving with regard to specific gravity, which can range from 1.020 to 1.025 without harm, provided it remains steady at the given value. The temperature of the aquarium also should not vary greatly and the preferred temperature is highly dependent upon the natural geographic range of the particular species. Please be very careful to match your seahorse species to the correct water temperature of its natural range. A species/temperature guide can be found here on page 4. Unlike most other fish, the calcium level in the aquarium is important to seahorses. Their bony exoskeleton depends on calcium to maintain its strength. Calcium levels from 350ppm and up should be sufficient.

Besides the usual menu of aquarium diseases or pathogens, such as Brooklynella, Uronema marinum, or trematodes, afflicting marine fishes, seahorses have to contend with a few additional health concerns. The biggest threat to their health is the fungus Gluea heraldi. This is a fatal sickness and is untreatable by aquarists. It is best to euthanize any seahorses that begin to show signs of this disease. Unfortunately, it is also highly infectious to other seahorse tankmates and even seahorses that share commonly used items such as nets and hydrometers with aquariums containing inflicted seahorses. It is imperative to act quickly once an accurate diagnosis has been rendered. The other concern for aquarists and seahorses alike is what has become known as the gas bubble disease. As the name implies, the male's brood pouch becomes filled with gas bubbles, resulting in a positively buoyant fish. These gas bubbles can be purged by pushing a thin, blunt object carefully into the brood pouch and releasing the trapped bubbles, but the problem will continue to affect the seahorse. For an in-depth review of most the common ailments affecting seahorses, including their causes and treatments, please refer to this detailed guide provided by Sygnathid.org.

Meet the Species

Despite having the widest distribution in the genus, Hippocampus histrix, known in the hobby as the Thorny Seahorse, is not seen in local retail outlets as often as some hobbyists may think. A wide variety of biotopes are suitable for this species, as it can be located from sea grass lagoons to mangroves, and even to 100 feet deep on reefs. Although it can live in shallow depths, the majority of this species' specimens are found at moderate depths, perhaps accounting for their limited availability in the trade. To adapt to such diverse biotopes the seahorse must be able to adjust its colors accordingly, and the Thorny Seahorse does just that. Colors of brown, white, and various shades of yellow are common, while shades of gray, green, and red have also been recorded. The largest specimen documented was less than six inches tall.

Hippocampus reidi is an often sought-after aquarium inhabitant. Its attractive coloring of bright yellow, red, and/or orange with accents of brown or black surely contributes to the amount of attention it receives within the hobby. This species is commonly available as captive bred specimens, making them all the more attractive. Although commonly referred to as the Brazilian Seahorse, they can, in fact, be found throughout Atlantic and Caribbean waters stretching from Bermuda to South America. They prefer to attach to gorgonians or sponges of similar color and thus should be offered the same holdfasts in aquariums. Five-inch adults are common, but most will not reach six inches.

Perhaps the most common of all aquarium specimens is Hippocampus kuda, fittingly called the Common Seahorse. Contributing to its availability are the captive breeding efforts, which have been rather successful. These are the Clydesdales of the ocean ponies, attaining a length of up to 12 inches. Similar to the previous two species, these are comfortable in temperatures ranging from the mid-70's to the lower 80's. Aquariums designed around bays and sea grass estuaries, which mimic its preferred natural habitat, are the best option.

Conclusion

Several species of Hippocampus are readily available in the marine aquarium trade. Additionally, many of them are also widely available as captive bred animals, thereby reducing the numbers of wild-caught fish and increasing the likelihood of the aquarist receiving healthy 'horses. When searching for seahorses, choosing a captive bred animal would be the smartest option. It may also be the only option within a few years' time. A Convention of International Trade in Endangered Species of Wildlife Fauna and Flora (CITES) regulation restricting the harvesting of seahorses less than 2.5" long went into effect this past May, and in all likelihood the restrictions could become even tighter in coming years. Currently, if an exporting country is unable to prove the collection of its native seahorses does not jeopardize the wild populations, it is not permitted to export the species. The time is now to govern ourselves and purchase only captive bred animals.

Acknowledgements

I would like to extend a special thanks to Project Seahorse for the wonderful photos and diagrams. If you have a chance, visit their site: Project Seahorse. Addtionally, many thanks are due to Leslie Leddo, Jeffrey Jeffords of Divegallery.com and Robert Sozzanni of Scubabob for the generous use of their awesome photos. Also, thanks to Laurence Richardson of www.NaturalHistoryArtist.com for the use of the excellent diagrams.

References:

Blumer, L. S. 1979. Male parental care in the bony fishes. Quarterly Review of Biology. 54: 149-161.

Gomon, M. F. 1997. A remarkable new pygmy seahorse (Syngnathidae: Hippocampus) from south-eastern Australia, with a redescription of H. bargibanti Whitley from New Caledonia. Mem. Mus. Victoria v. 56 (no. 1): 245-253.

Horne, M. L. 2001. A new seahorse species (Syngnathidae: Hippocampus) from the Great Barrier Reef. Rec. Aust. Mus. 243-246.

Kuiter, R. H. 2003. A new pygmy seahorse (Pisces: Syngnathidae: Hippocampus) from Lord Howe Island. Rec. Aust. Mus. 113-116.

Kuiter, R.H., 2001. Revision of the Australian seahorses of the genus Hippocampus (Syngnathiformes: Syngnathidae) with descriptions of nine new species. Rec. Aus. Mus. 53:293-340.

Kuiter, R. H. 2000. Seahorses, Pipefishes, and Their Relatives. TMC Publishing. Chorleywood. 240pp.

Lieske, E. and R. Myers, 1994 Collins Pocket Guide. Coral reef fishes. Indo-Pacific & Caribbean including the Red Sea. Haper Collins Publishers. 400 p.

Lourie, S.A., A.C.J. Vincent, H.J. Hall. 1999. Seahorses: an identification guide to the world's species and their conservation. London: Project Seahorse.

Lourie, S.A. and J.E. Randall, 2003. A new pygmy seahorse, Hippocampus denise (Teleostei: Syngnathidae), from the Indo-Pacific. Zool. Studies 42(2):284-291.

Michael, S.W. 1998. Reef Fishes Volume 1. Microcosm. Shelburne. pp. 624.

Michael, S.W. 1999. Marine Fishes: 500 + Essential-To-Know Aquarium Species. Microcosm. Shelburne. pp. 448.