Reply To: H. Zosterae salinity/ density

Pete Giwojna

Dear Eve:

Personally, I favor the lower range of the optimum salinity for Hippocampus zosterae at around 1.019 simply because it’s possible that the lower salinity might help prevent some of the invertebrate pests that plague dwarf seahorses, such as hydroids, nematodes, and aiptasia rock anemones, from becoming established in your setup.

Here is a copy of my species summary on Hippocampus zosterae that will provide you with additional information about these pixie-like ponies:

Hippocampus zosterae (Tropical to Subtropical, Benthic)
Common name: Dwarf Seahorses, Sea Ponies, Pygmies or Pigmies, and Pixies (US).
Scientific name: Hippocampus zosterae Jordan & Gilbert, 1882
Hippocampus regulus
Hippocampus rosamondae
Maximum size: 2 inches (5.0 cm) in total length.
Climate: subtropical to tropical: 20° N to 30° N.
Western Atlantic: Bermuda, southern Florida, Bahamas and the entire Gulf of Mexico.
Meristic Counts:.
Rings: 9-10 trunk rings + 31-32 tail rings.
Dorsal fin rays: 12 soft rays spanning 2 trunk rings + 0 tail rings.
Pectoral fin rays: 11-12 soft rays.
Snout length: 4.2-4.3 in head length. In other words, the length of the snout will fit into the seahorse’s head length more than four times (i.e., they have very short, stubby snouts that are usually < 1/4 the length of their heads).
Other distinctive characters:
Coronet: high, columnar or knob-like, without spines or projections.
Spines: low or knob-like.
Cirri: variable — some have none, others are very shaggy due to profuse cirri.
Key Features: short snout (always <1/3 to 1/4 their head length).
Adult height: 3/4 inch to 1-3/4 inches (2 to 4-1/2 cm).
Color and Pattern:
Dwarf seahorses can be extremely variable in coloration. Their base coloration is typically beige or fawn, but may be dark brown, gray, or oyster shell white and colorful sports of every description occur occasionally. Their normal pattern is a mottled fawn color, but greenish, yellow, black, brown, and pearly specimens are fairly common, and saddles, blotches, ringed-tails, and pinto- and bumblebee-like patterns are seen from time to time (Giwojna 1990; Giwojna, Jun. 2002). Many specimens are marked with white flecks like splashes of paint and a dark sub-marginal stripe on the dorsal fin is a common feature.

Breeding Habits:
Breeding Season: mid-February to late October, as determined by day length.
Gestation Period: about 10 days, depending on temperature and diet.
Egg Diameter: 1.3 mm.
Brood Size: 5-55 fry; occasional large broods up to 70 fry have been reported, but two dozen fry is much more typical.
Size at Birth: 1/3 inch (7-9 mm)
Onset of sexual maturity: fry grow rapidly, reaching maturity after 2-3 months.
Pelagic/Demersal (benthic): benthic; newborns orient to the substrate and seek out hitching posts immediately after birth.

Ease of Rearing:
As easy as it gets. Many home hobbyists have closed the life cycle with this species and H. zosterae is widely considered to be the easiest of all seahorses to raise. Eminently well suited for the easy rearing method.

Natural Habitat:
H. zosterae is restricted to seagrass microhabitats in shallow water, and is typically found living in association with the seagrass Zostera (Bull and Mitchell, 2002, p56), for which the species is named.
Natural History:
The dwarf seahorse resides in shallow grass flats amidst Zostera and other seagrass and is also known for its rafting ability, commonly being found in mats of floating Sargassum. It occurs in the coastal Gulf of Mexico, Bahamas, Bermuda, the Florida Keys, Florida’s East Coast, Old Tampa Bay, Lemond Bay, Pensacola, and Texas (Bull and Mitchell, 2002, p56).
These tiny seahorses are tough as nails, a legacy of their shallow, inshore environment in which the water conditions typically range from 43° F to 98° F (6°C-37°C) and from marine to brackish (40% fresh water) during the seasons. They tolerate extremes that would be fatal to most other fishes and can adapt to a wide range of temperatures and salinity in the aquarium, but they are most common in bays during periods of high salinity and prefer the specific gravity to be maintained in the low normal range (1.019-1.022). They are diurnal seahorse that are active by day, and their aquarium should be lighted at least 12 hours a day since their breeding season is determined by day length (they stop reproducing when there is less than 12 hours of daylight) (Strawn 1954).
H. zosterae has been well studied in the field and in the laboratory, and research has determined that the dwarf seahorse forms monogamous pairs in the wild that court early each morning until mating occurs (Masonjones and Lewis 1996). Four distinct phases of courtship precede pair formation and mating (Masonjones and Lewis 1996). The first phase of courtship lasts for one or two mornings prior to the actual mating and consists of repeated bouts of reciprocal quivering in which the male and female brighten and alternately engage in a series of rapid (12 cycles per second) side-to-side body vibrations (Masonjones and Lewis 1996). When one of the seahorses stops quivering, its partner must pick up where it left off and resume shimmying within 5 seconds (Masonjones and Lewis 1996). Back and forth, the pair will exchange repeated series of quivering throughout the morning of the first day(s) of courtship.
The remaining 3 phases consist of new behaviors that all appear during the final day of courtship and build up inexorably to the grand finale. In the second phase, the female begins to Point and the male responds with displays of Pumping (Masonjones and Lewis 1996). In the third phase, the male begins to echo the female’s Points by Pointing in return (Masonjones and Lewis 1996). And in the final phase of courtship, the pairs repeatedly rise together in the water column, eventually leading to a brief midwater coupling during which the females deposits her eggs in the male’s brood pouch (Masonjones and Lewis 1996).
One a pair has formed in this manner, the partners are believed to remain together and mate exclusively with each other throughout the breeding season in the wild (Masonjones and Lewis 1996). The female normally re-mates with the male 4-20 hours after he gives birth to his latest brood (Masonjones and Lewis 1996). Interestingly, although these miniature ponies are but a fraction the size of H. reidi, female dwarves produce eggs that are slightly larger (egg diameter is 1.3 mm) than the ova reidi mares produce (Lourie, Vincent & Hall 1999).
The breeding season extends from February to October, and the males deliver anywhere from 5 to 55 fry after a gestation period of just 10 days. Considering the tiny size of the males and the very short period of gestation, newborn H. zosterae are surprisingly large (7-9mm) and well developed (Bull and Mitchell, 2002, p56). They immediately orient to the bottom and seek out hitching posts, and are able to eat newly hatched brine shrimp (Artemia nauplii) right from birth. The young grow very rapidly, more than doubling in size after their first 17 days (Bull and Mitchell, 2002, p56), and within a mere 2-3 months they are already producing offspring of their own. When fully grown, they will only 1 inch to 1-3/4 inches (2.5-4.5 cm) long (Bull and Mitchell, 2002, p56).
This accelerated life cycle is necessary because dwarves have a very short life expectancy in the wild. Very few adults survive their first winter, and to my knowledge none of them have ever been known to overwinter twice (Strawn 1953, 1958). That makes their maximum lifespan about 1-1.5 years in their natural habitat. But they are amazingly resilient and these diminutive denizens of the deep cram a whole lot of living into that short period. In 85 F (30 C) water, a male will have at least two broods a month, with the young developing very quickly during the summer months and becoming sexual mature in only 2 to 3 months. That means a male that delivers his first brood in mid-February can easily produce a dozen broods or more during the breeding season, and may become a great-great-grandfather by the end of the season in October. Amazing animals!

Preferred Parameters:
Carol Cozzi-Schmarr recommends that Ocean Rider’s captive-bred-and-raised dwarf seahorses (H. zosterae) be maintained under the following conditions:
Temperature = range 68°F to 80°F (20°C-27°C), optimum 75°F (24°C).
Specific Gravity = range 1.018 – 1.024, optimum 1.019-1.022
pH = 8.2 – 8.4
Ammonia = 0
Nitrite = 0
Nitrate = 0-10 ppm
Suggested Stocking Density: 2 pairs per 1 gallon (4 liters).

Aquarium Requirements:

Because of their small size, dwarf seahorses are best suited for a small aquarium of 5-10 gallons (19-38 liters). The water quality parameters should be as described above.

I prefer a very basic setup for keeping dwarf seahorses (Hippocampus zosterae). Depending on the size of my herd, I like anything from a standard 2-1/2 gallon to a 10-gallon tank (all glass construction, of course — no stainless steel), equipped with a glass top and an ordinary strip reflector.

For filtration, I keep things really simple, using only air-operated sponge filters or a well-maintained undergravel filter that covers the bottom of the tank completely on dwarf tanks. I know undergravels are considered old-fashioned technology nowadays, but they are inexpensive, utterly reliable and foolproof (no moving parts), easy to install, and work extremely well for dwarf seahorses with no modification whatsoever. An inexpensive diaphragm air pump will operate the filter and provide all the aeration you need.

Sponge or foam filters provide all the same advantages of undergravels and more. So in actual practice, I normally prefer foam filters over undergravels for smaller dwarf tanks, simply because the foam filters are easier to clean and maintain, and are quite a bit more versatile than the undergravels.

Avoid sponge filters with weighted bottoms or other metal components, however, since they will rust when exposed to saltwater. Sooner or later this will cause problems in a marine aquarium (sooner in the small setups that are most suitable for H. zosterae). Select a sponge filter that has no metal parts and is safe for use in saltwater. The proper units will have suction cups to anchor them in place rather than a weighted bottom.

Cleaning the foam filters is a snap. Simply immerse them in a bucket of saltwater and gently squeeze out the sponge until it’s clean and releases no more sediment or debris. Run a bottlebrush through the inside of the tube, wipe off the outside of the tube, and you’re done. The filter is ready to go back in the aquarium with no impairment at all of the biofiltration. Takes only a couple minutes.

I like to keep a few extra sponge filters running in my sump or a refugium at all times. That way, I’ve got instant, fully established, portable biofilters I can use wherever needed — a hospital ward or quarantine tank, a nursery tank or rearing tank, a brand new setup, or anytime the biofiltration needs a boost in another tank for any reason. Very versatile! You’ll never realize how valuable an instant biofilter can be until you really need one.

I find sponge filters and undergravels are generally the best option for dwarf seahorses because most other types of filtration aren’t practical in such small setups. Power filters would turn a 2-1/2 or 5 gallon tank into a maelstrom, battering pigmy ponies around. And power filters have a bad habit of “eating” dwarf seahorses and filtering out all the Artemia nauplii before the seahorses can make a dent in it.

I still use rock in my larger dwarf setups, but it’s “dead” foundation rock that quickly enough becomes alive as it’s overgrown by algae and inhabited by copepods, amphipods and myriad microfauna. It looks completely natural when surrounded by living, growing macroalgae, which is primarily how my dwarf tanks are decorated.

A lush bed of assorted Caulerpa dominates the rear third of my current dwarf tank, completely concealing the sponge filters. The Caulerpa consists of various long-bladed and plumed or feathery varieties such as Caulerpa sertularioides, Caulerpa mexicana, Caulerpa ashmedii, Caulerpa serrulata and Caulerpa prolifera. The center of the tank is aquascaped with more macros — mostly red and gold species of Gracilaria (Hawaiian Ogo), plus a seahorse tree centerpiece and yet more Caulerpa. Other decorative macros are arranged in the foreground of the aquarium where the light is brightest: a cluster of Merman’s Shaving Brushes (Penicillus capitatus) and a stand of Halimeda sea cactus, interspersed with Udotea palmate fans. The result is a colorful macroalgae garden with a very nice contrast of colors (reds, yellows, greens, and brown) and interesting shapes. A tank heavily planted with macros such as these is a lovely sight and mimics the dwarf seahorse’s natural seagrass habitat well.

As an added benefit, the macroalgae act as an excellent form of natural filtration, supplementing the sponge filters, and reducing the available levels of phosphates and nitrites/nitrates. When we prune and trim back the fast-growing Caulerpa regularly and remove the clippings, we’re actually exporting phosphates, nitrates and other nutrients from the tank, thereby helping to maintain good water quality.

For the substrate with sponge filters, I like a bed of fine grained black sand about 3/4-inch to 1-inch deep, both for it’s pleasing appearance and to accommodate Nassarius snails, which like to bury in the sand bed. The Nassarius snails and Scarlet Reef hermit crabs (Paguristes cadenati) are the cornerstones of the clean-up crew in my dwarf tanks. The Scarlet Reef micro-hermits are colorful and interesting in their own right, and these harmless herbivores are the only hermit crabs I trust with my dwarf seahorses. A half dozen of the colorful Scarlet Reef crabs make nice additions for a dwarf seahorse tank, as do the Nassarius snails, which are very active, efficient scavengers that handle the meatier leftovers.

I do small weekly (15%-20%) or biweekly water changes of 10%-15% on my dwarf tanks, rather than the monthly or bimonthly water changes I perform on large setups, but the volume of the water exchanged is so small — just a gallon or so at most — that they are a breeze. Heck, if I mix up a 5-gallon bucket of new artificial salt mix in advance, that provides enough clean, aged saltwater for a month’s worth of water changes on my dwarf tank. When I siphon out the water for the weekly exchanges, I use the opportunity to vacuum the substrate and tidy up the tank a bit. Once it settles, I use the water I siphoned out to clean the sponge filters. The whole process, water change and all, takes all of 10 minutes.

But that 10 minutes of weekly maintenance returns wonderful rewards in terms of water quality. With such a small volume of water, the conditions can deteriorate quickly in a dwarf tank, and this modicum of weekly maintenance keeps things running smooth and trouble free.

In short, my current dwarf seahorse setup is basically a 5-gallon tank equipped with two air-operated sponge filters for biological and mechanical filtration, plus lush beds of macroalgae for natural filtration, simulating the pigmy ponies’ seagrass habitat. This is a very simple, inexpensive, low-maintenance aquarium that’s extremely easy to set up, yet it’s also quite attractive and a very fun display.

It’s currently housing a breeding colony of about 15 adults and all their offspring and it’s far from overcrowded. With that many adults, I find I have at least one pregnant male at any given time, usually more, and births virtually every week. I find it endlessly fascinating to witness the seahorse’s entire cycle of life taking place in microcosm — courting, mating, giving birth, newborns, juveniles and young adults all thriving and growing right alongside the old warhorses.

When my herd of zosterae grows a little more, it will be time to upgrade to a bigger tank. For all practical purposes, I find 25-30 adults can be maintained in a 10-gallon tank set up as described above before water quality becomes problematic (especially if your are raising the young with their patents). Rather than sponge filters, I prefer to use an undergravel filter in conjunction with a very small power filter for a heavily stocked 10-gallon dwarf tank such as that. For such a system, I use an undergravel filter with a single uplift tube and mate the intake tube from the power filter to the UG uplift, so that all the water that goes through the filter first passes through a gravel bed 2-3 inches deep. That simple modification both improves the efficiency of the undergravel filter and prevents the power filter from engulfing dwarf seahorses or their food supply. The small power filter allows filter media such as polyfilter pads and a good grade of activated carbon to be used in the dwarf tank.

Although beginners will be better off keeping a modest herd of dwarves in a small, simple setup like those I’ve described above, there is another type of dwarf tank that works very well for more advanced aquarists. It allows dwarves to be kept in much bigger tanks than is otherwise possible by partitioning or compartmentalizing a large aquarium.

Ordinarily, this is done by using perforated tank dividers to separate a 20-30 gallon (75-114 liters) aquarium into two sections — an equipment area for the filters and such, and a living area for the dwarf seahorses. The perforated barrier allows water to circulate freely between the areas while acting as a baffle that greatly dampens the turbulence generated on the equipment side.

There are some definite advantages to keeping dwarves in a big aquarium this way. For one thing, the larger volume of water gives the aquarium greater stability as far as fluctuations in temperature and pH go, makes it easier to maintain optimum water quality, and just generally gives the hobbyist a greater margin for error. For another, it gives the dwarf keeper better filtration options. For instance, you can’t get a decent protein skimmer for a setup of 5 gallons or less, and power filters create way too much turbulence in small tanks for Pixies. No such problems with the big subdivided tanks. Such setups allow the dwarfs to benefit from the lower volume of water and superior filtration such a system provides, yet the smaller living area makes it easier to maintain a proper feeding density for the pigmy ponies than would be possible in an undivided tank.

For complete details and instructions for setting up the type of dwarf tanks discussed above, as well as other aquarium options for keeping H. zosterae, see Alisa Wagner Abbott’s outstanding new book on dwarf seahorses (The Complete Guide to Dwarf Seahorses in the Aquarium, 2003, 144 pages). It’s the only aquarist’s guidebook ever to be devoted entirely to dwarf seahorses. It includes excellent, up-to-date information, on every aspect of their care and keeping, including breeding and rearing, population dynamics, and maintaining a self-sustaining colony. All in all, a wonderful resource for the dwarf seahorse keeper.

Tankmates for Dwarf Seahorses

Although their small size does indeed limit the suitable tankmates that can be kept with dwarf seahorses, I have found small pipefish do well with H. zosterae. I have a pair of small Gulf Pipefish (Syngnathus sp.) from Florida in my dwarf tank, which add a lot of interest to the aquarium because their behavior is so different from the dwarves (Giwojna, 2005). For example, when they’re just trying to blend into their surroundings, the pipes orient themselves vertically, heads up and tails down, and sidle up alongside a fake gorgonian or a tall clump of sea cactus, imitating one of the branches. It’s not a bad bit of camouflage, and once in a while one of the seahorses perches on a pipefish by mistake and gets taken for a wild ride, like a bareback bronco rider at a rodeo.

But when they’re hunting, the pipes slip into the beds of Caulerpa horizontally, and launch themselves like torpedoes at passing prey (Giwojna, 2005). Unlike the seahorses, which prefer to wait for their prey to come to them, the pipes dart out from hiding and snatch up brine shrimp right and left. It’s amazing how much faster and more agile they are than the pigmy ponies. At feeding time, the pipes go blasting around the tank like little guided missiles. Fortunately, with just two pipefish in the tank, they can’t make a serious dent in the swarms of Artemia.

Like the seahorses, these pipefish are livebearers and give birth to independent babies that are miniature replicas of themselves, except that the newborn pipes are totally transparent (Giwojna, 2005). They look like glass splinters or tiny transparent threads. Although I never made a serious attempt to raise them, a number of them survived for several weeks when left to their own resources in the dwarf tank. They were very good at concealing themselves amid the macroalgae, and especially liked to take refuge amongst the “bristles” of my Merman’s Shaving Brushes. The dwarf seahorses have no interest in them whatsoever, but I strongly suspect the parent pipes are cannibals. All in all, Gulf pipefish are inexpensive and entertaining additions to my dwarf seahorse setup.

For a nice splash of added color and natural beauty, I also like to add an assortment of Feather Dusters (Sabellastatre magnifica and Sabella sp.) amidst my beds of macroalgae. They are the brightly colored flowers blooming among all the greenery of this underwater garden. Feather Dusters are exotic, very showy, entirely harmless, relatively inexpensive, and completely compatible with dwarf seahorses (Giwojna, 2005). They are filter feeders and seem to eat the same newly hatched brine shrimp as dwarf seahorses, but they do best when fed phytoplankton (or commercial food preparations designed for filter-feeding invertebrates) with a baster from time to time.

The Lettuce Nudibranch (Elysia crispata, formerly known as Tridachia crispata, and still usually sold under that name) is another showy, totally innocuous invertebrate that’s a perfect choice for a dwarf seahorse companion. It is green with lavender spots and is covered with extravagant frills and ruffles that look like flower petals on an exotic orchid, but in fact they are the ruffled flaps of tissue (parapodia) that outline each side of the back of this two inch sea slug that lives in the waters of the Caribbean and Florida Keys (Giwojna, 2005). It’s an algae eater that dineson macroalgae such as Caulerpa sertularioides and is one of the few nudibranchs that do well in the aquarium, particularly a dwarf tank with a lush bed of Caulerpa (Giwojna, 2005).

I also have a handful of Volcano shrimp or Hawaiian red feeder shrimp (Halocaridina rubra) in the tank, not as food for the dwarf seahorses but rather as their tankmates. These colorful little saltwater shrimp resemble miniature peppermint shrimp, and usually do well with dwarves because of their size. They are too big to be eaten by the seahorses and too small to be any threat to them, and as an added bonus, they will produce larval shrimp that are perfect treats for the ponies. They are omnivores that do a fair job of scavenging and complement the regular clean-up crew nicely (Giwojna, 2005).

Along with the Volcano shrimp, Nassarius snails and Scarlet Reef hermit crabs (Paguristes cadenati) can serve as the cornerstones of the clean-up crew for dwarf seahorse tanks. The Scarlet Reef micro-hermits are colorful and interesting in their own right, and these harmless herbivores are the only hermit crabs I trust with my dwarf seahorses. A few of the colorful Scarlet Reef crabs make nice additions for a dwarf seahorse tank, as do the Nassarius snails, which are very active, efficient scavengers that handle the meatier leftovers.

Most starfish must be avoided when keeping dwarf seahorses because they are a threat to the pigmy ponies and their young, but there are a couple of exceptions to this rule. For example, the Red Bali Starfish (Fromia milliporella) is a small, nonaggressive starfish that feeds primarily on detritus and meiofauna on sandy substrates. The Red Bali Starfish is a tiny species that doesn’t grow to more than 3 inches in diameter (most aquarium specimens are only 1-2 inches in arm span). They thrive in a well-established aquarium with macroalgae and a sand substrate.

Also worth considering are the tiny brittle starfish commonly known as Micro-Stars and often marketed as aquarium scavengers or sanitation engineers under that name. They start small and stay small, with a leg span that never exceeds the diameter of a 25-cent piece even when they are fully grown (most of these miniature brittle stars cannot span a 5-cent piece). Their legs are often attractively banded and they are very active and agile scavengers, moving more like miniature octopus that slowpoke sea stars. The micro-stars are fascinating in their own right, but it’s best to limit yourself to one or two of them, since they reproduce very quickly when conditions are to their liking.

Dwarf seahorses are generally considered the easiest of all seahorses to raise. While rearing them is still a challenge, once they’ve gained some valuable experience and straightened out their learning curve, many hobbyists find their dwarf seahorse herds grow steadily. With a short gestation period of around 10 days, and rapidly growing young, H. zosterae will produce three generations in a single year under ideal conditions, which means before long many dwarf seahorse keepers find themselves looking for a larger setup. My own dwarf tank is again fast approaching that point, leaving me with three options: set up a second dwarf tank, move the entire colony into a bigger tank, or find homes for my excess livestock among my fellow hobbyists.

It’s a nice problem to have. And few things are more rewarding to an aquarist than handing out healthy homegrown seahorses to your admiring friends!

Juvenile Rearing Tanks:

Cannibalism is unknown in H. zosterae, and one of the neat things about them is that the fry can be reared in the main tank right alongside their parents since the newborns eat the same foods as the adults. However, for best results, the fry should be reared in a separate nursery tank where the hobbyist can maintain better control over their feeding, growth and development (Bull and Mitchell, 2002, p57). A basic benthic nursery with sponge filters works great for this and can be set up in much the same way as the adult tanks.

More frequent maintenance is required for the nurseries, however. With heavy, continuous feedings in such a small volume of water, regular siphoning is necessary to maintain water quality (Bull and Mitchell, 2002, p57). Fecal pellets and debris should be siphoned from the bare-bottomed nurseries at least twice a day with the deficit made up with new seawater (Bull and Mitchell, 2002, p57). The sponge filters must also be cleaned often as described previously.

The benthic fry thrive on newly hatched brine shrimp (Artemia nauplii) with small, frequent feedings that provide live prey throughout the day. They seek out hitching posts from birth, meaning the fry rarely gulp air, floaters and surface huggers are virtually nonexistent, and they are largely immune from the buoyancy problems that so often plague pelagic seahorse fry.

Experienced aquarists often achieve good success rates (better than 20% survival) in rearing H. zosterae to adults using these simple methods (Bull and Mitchell, 2002, p57).

Diet, Nutrition, and Feeding Techniques:

Adults do well on a staple diet of enriched Artemia nauplii at various stages of development, which have been fortified by feeding the brine shrimp “greenwater” phytoplankton or special enrichment products rich in HUFA (Bull and Mitchell, 2002, p57). Enriched brine shrimp should be offered at least 3 times a day or as often as is convenient (Bull and Mitchell, 2002, p57). This basic diet can be supplemented liberally with copepods, plankton, rotifers, small amphipods and the larval stages of Mysids, ghost shrimp and many other shrimp. If you can possibly provide them, copepods are the ideal food for H. zosterae. Research indicates that in some locations the dwarf seahorse’s diet consists primarily of harpacticoid copepods (Tipton and Bell 1988).

Newborn dwarf seahorses require a constant supply of newly hatched brine shrimp (Artemia nauplii) for the first 2-3 weeks of life until they are big enough to begin taking larger brine shrimp (Bull and Mitchell, 2002, p57).

Some success at getting dwarf seahorses to accept nonliving foods has also been reported by hobbyists. A commercial product consisting of Cyclops copepods in frozen form is sometimes accepted by H. zosterae (Alisa Abbott, pers. comm.) Some hobbyists have also been able to wean dwarf seahorses onto a diet of minced frozen mysids by using juvenile erectus that greedily eat the frozen mysids as role models to teach the dwarves that its edible (Liisa Coit, pers. comm.). The eager feeding of the young erectus appears to stimulate the interest (and appetite) of the H. zosterae and encourages them to try the new food.

If you are interested in attempting to wean dwarf seahorses onto nonliving food such as chopped frozen Mysis, you should wait until they are at least 3 weeks old to begin training them. Keep in mind that they will not be able to take larger pieces of Mysis until they are 3 months old, and be very diligent about cleaning up any leftovers after each training session. Using a role model to teach them the ropes is especially helpful. Be advised, however, that some dwarf seahorses simply never learn to eat frozen foods no matter how much training or coaxing they receive.


Commonly known as the dwarf seahorse, Hippocampus zosterae is the smallest of all the seahorses available to hobbyists. Dwarf seahorses reach a maximum size of about 1.75 inches or 45 mm, half of which is tail. To me, their diminutive dimensions are a source of endless delight; I find them quaint and charming in the extreme (Giwojna, Jun. 2002).
Many specimens are adorned with numerous cirri, giving them a shaggy or weedy appearance that adds to their charm (Giwojna, Jun. 2002). In some individuals, these fancy skin filaments are developed to such an extravagant extent they look downright fuzzy (Giwojna, Jun. 2002).

As I described them in the June 2002 issue of Freshwater And Marine Aquarium: “Of all the seahorses, these exquisite animals were my first love. Thirty years ago, they were the easiest seahorses to feed, accepting newly hatched brine shrimp as their staple diet from the cradle to the grave (Giwojna, Jun. 2002). I could breed them, raise them, and keep them healthy throughout their normal life span at a time when undergravel filters were new and controversial — the cutting edge of aquarium technology (Giwojna, Jun. 2002). My “nursery tank” for the first fry I ever raised to maturity was a mayonnaise jar I rescued from the trash (no such thing as recycling back in those days) (Giwojna, Jun. 2002)!

They remain among my favorite seahorses today, and my preferred setup for keeping them is still a basic 2 to 2.5-gallon aquarium equipped with simple undergravel or foam filters. I find that dwarves tend to get lost (visually that is — the tank appears barren or empty at first glance) in anything much larger than that, and it becomes increasingly difficult to maintain an adequate feeding density of baby brine shrimp for the fry in systems bigger than about 10 gallons unless the tank is partitioned off or subdivided (Giwojna, Jun. 2002).

Dwarves breed best in large groups and are the most sociable of all the seahorses. What makes it extra fun is that these pint-size ponies are as prolific as they are promiscuous. Any time you have an adequate number of H. zosterae together — say several pairs — and conditions are to their liking, mating is a foregone conclusion. Once your dwarf seahorse herd includes 10-12 adults, you can be sure that one or more of the males will be pregnant during the breeding season at all times.”

Heck, anytime you order several pairs of dwarves during the months of May to August, the height of their breeding season, you’re virtually guaranteed that some of the males will be pregnant when they arrive (Abbott 2003). In that case, expect your first dwarf babies to be born in the shipping bags en route or while you’re acclimating your new additions or immediately after you introduce them to the aquarium (Abbott 2003). Or all of the above. Happens all the time!

Far from inhibiting courtship, crowding seems to stimulate breeding in dwarf seahorses, almost as if they reach “critical mass” at a certain population density, triggering a chain reaction of mating attempts. Thus, provided water quality can be maintained, “the more the merrier” appears to be the rule with this species.

For instance, pet dealers must occasionally crowd large numbers of fish together in cramped quarters due to a lack of space, including dwarf seahorses. Robert Straughan was once forced to keep 300 H. zosterae in a 10-gallon tank in such a situation back in the old days, and was pleasantly surprised to find that over 100 of them managed to pair off and breed nonetheless. He reported that at any given moment, dozens of dwarves were actively engaged in courtship, so it was a common sight to witness several couples rising simultaneously to exchange eggs, and that one or more of the gravid males would be delivering young virtually around the clock (Straughan, pers. comm.)!

In terms of their hardiness, fitness for aquarium life, prolific breeding habits, and ease of rearing, dwarf seahorses should be considered the guppies of the sea (Giwojna, Jun. 2002). In fact, this is one seahorse that may enjoy a greater life span in captivity than the wild (Giwojna, Jun. 2002). In nature, winter storms and hurricanes take a heavy toll on their numbers, and very few adult dwarf seahorses survive their first winter; none are known to overwinter twice (Giwojna, Jun. 2002). A detailed field study marked all the individuals of a Cedar Key population and followed them closely for a period of several years (Strawn 1958). The study revealed that the Cedar Key dwarves grew fast, reached sexual maturity early (within 3 months), and died young, with few surviving for more than a year (Strawn 1953; 1958). No 2 year-old specimens were ever observed. (Strawn 1953; 1958) Thus, their natural life span is believed to be about one year in the ocean. In captivity, experienced hobbyists have kept them for 3+ years and not only can they survive to that ripe old age, they are still going strong and may even keep breeding well into their third year. As with other farm-raised seahorses, expect the captive-bred dwarf seahorses to be even hardier than their wild-caught conspecifics.

Nematodes can be a chronic problem with wild-caught dwarves and pigmy seahorses keepers are often plagued by hordes of hydroids and Aiptasia anemones–colonial stinging organisms that kill zosterae babies and injure the adult seahorses, which often subsequently succumb to secondary infections (snout rot; tail rot) (Giwojna, Jun. 2002).
These cnidarians often explode to plague proportions in dwarf tanks because they thrive on the newly hatched brine shrimp that’s fed to the ponies. These persistent pests are the single greatest cause for failure among dwarf seahorse keepers (Abbott 2003).

Nematodes and hydroids (or their hydromedusae stages, which are micro-jellyfish) often enter the aquarium right along with the wild-caught specimens. They typically arrive with WC zosterae or their tankmates, or are introduced shortly thereafter on live plants or live foods (Giwojna, Jun. 2002). Once they gain a foothold in the aquarium they are extremely difficult to eradicate. In fact, once hydroids appear in a dwarf tank, most hobbyists deal with the problem by dismantling the aquarium, sterilizing everything, and starting over from scratch (Alisa Abbott, pers. comm.). Experienced dwarf seahorse keepers often run duplicate setups for that very reason. One tank is the seahorse exhibit; the other is established as a backup tank, held in reserve for the dreaded day when the hydroids appear (Alisa Abbott, pers. comm.). That way, when an infestation inevitably breaks out, the specimens can be given a freshwater dip and transferred safely to the standby tank while the infested tank is taken down, sterilized, and reestablished anew to serve as the backup tank for the next outbreak (Alisa Abbott, pers. comm.).

This is where the domesticated dwarves, farm-raised in Hawaii, have an enormous advantage over wild-caught dwarf seahorses from Florida (Giwojna, Jun. 2002). The CB H. zosterae reach the hobbyist completely free of hydroids and ectoparasites (Giwojna, Jun. 2002). Providing they are then fed with decapsulated Artemia (the decapping process eradicates any and all pathogens or parasites the brine shrimp cysts may have been harboring), chances are great the dwarf seahorse keeper will never have to deal will nematodes or wage war against an invasion of hydroids (Giwojna, Jun. 2002). The trouble-free day of the all-but-indestructible dwarf seahorse has finally dawned (Giwojna, Jun. 2002)!

Cultured H. zosterae are the only captive-bed seahorses that are not pre-trained to eat frozen Mysis (Giwojna, Jun. 2002). The tiny size of these pigmy ponies precludes that possibility. Fortunately, they will thrive on a steady diet of easy-to-provide enriched brine shrimp (Artemia) of all stages from newly-hatched to adult (Giwojna, Jun. 2002). But if you are really interested in dwarf seahorses, I wouldn’t let the fact that they need live food deter you in the least from keeping these amazing little marvels! Hatching brine shrimp for dwarves is a daily chore, but it’s not difficult and quickly becomes routine. Moreover, it is a chore that every seahorse keeper must master sooner or later. Regardless of what species of seahorse you keep, if you want to raise their offspring, you will need to hatch out brine shrimp on a daily basis since that’s the first food most newborns accept. And with dwarf seahorses you are assured that you will always have plenty of fry to raise!

Bottom Line:

Dwarf seahorses are great for beginners and ideal for breeders. Pint-sized and prolific, these pigmy ponies are the perfect pick for anyone primarily interested in rearing or for any seahorse keepers who can’t afford to devote too much money or space to their hobby. Hippocampus zosterae is the best choice for the novice who wants to learn more about keeping and breeding seahorses before moving on to the big boys. More budding seahorse keepers have cut their teeth on dwarves than all the other seahorses put together. H. zosterae is the right pick for newbies who would like to try their hand with seahorses for a modest investment, or for hobbyists with a tight budget, or aquarists looking for captive-bred seahorses that are a snap to breed and a breeze to raise, or anyone captivated by keeping tiny elfin creatures no bigger than your thumbnail. This species gets my highest recommendation.

However, H. zosterae is not a good choice for hobbyists with tanks larger than 10-20 gallons (38-76 liters) for the reasons mentioned above. And this is NOT the seahorse for anyone who minds hatching out brine shrimp on a daily basis.

Additional Information (to learn more about Hippocampus zosterae, please consult the following references):

Abbott, Alisa Wagner. 2003. The Complete Guide to Dwarf Seahorses in the Aquarium. Neptune City, NJ: TFH Publications.

Heuter, Joanne. 1997. “The Dwarf Seahorse (Hippocampus zosterae).”

Hippocampus zosterae, Dwarf seahorse. 23 Feb. 2004. Fish Base. <;

Masonjones, H. D. and S. M. Lewis. 1996. “Courtship behaviour in the dwarf seahorse, Hippocampus zosterae.” Copeia. 1996(3): 634-640.

Masonjones, H. D. 1997. “Sexual selection in the dwarf seahorse, Hippocampus zosterae (Syngnathidae): An investigation into the mechanisms determining the degree of male vs. female intrasexual competition and intersexual choice.” PhD thesis, Tufts University, U.S.A.

Masonjones, H. D. and S. M. Lewis. 2000. “Differences in potential reproductive rates of male and female seahorses related to courtship roles.” Animal Behaviour, 59: 11-20.

Masonjones, H. D. 2001. “The effect of social context and reproductive status on
the metabolic rates of dwarf seahorses (Hippocampus zosterae).” Comparative
Biochemistry and Physiology A 129, 541–555.

Strawn, Kirk. 1953. “A Study of the Dwarf Seahorse, Hippocampus regulus Ginsburg, at Cedar Key, Florida.” M.Sc. Thesis, University of Florida, 1953.

Strawn, Kirk. 1954. “Keeping and breeding the dwarf seahorse”. Aquarium Journal 25(10), 1954: 215-218, 227, 228.

Strawn, Kirk. 1958. “Life history of the pigmy seahorse Hippocampus zosterae Jordan
and Gilbert, at Cedar Key, Florida.” Copeia, 1958: 16-22.

Tipton, K. and S. S. Bell. 1988. “Forging patterns of two syngnathid fishes: importance of harpacticoid copepods.” Marine Ecology — Progress Series. Vol. 47: 31-43.

Do you have a copy of Alisa Abbott’s guidebook (Complete Guide to Dwarf Seahorses) yet, Eve? That’s one book every Pixie owner and dwarf seahorse keeper should have on hand. I’ve proofed Alisa’s dwarf seahorse book for TFH publications and wrote the preface for it, and I highly recommend it!

Pete Giwojna, Ocean Rider Tech Support

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