The best container or nursery tank for your fry depends largely on what species of seahorse you raise and whether or not the fry go through an extended pelagic phase, as discussed below.
As you know, all seahorse babies are challenging to raise and Ocean Riders are no exception. How difficult or challenging they may be depends on the type of seahorses you have. Two main factors determine how easy or hard seahorse fry are to raise: (1) their size at birth and (2) whether or not they undergo a prolonged pelagic phase. The bigger and better developed the newborns are, the easier they are to raise. Seahorse fry whose average length at birth is 10 mm (0.4 inches) or more are able to take enriched Artemia as their first foods and are relatively easy to rear. Seahorse fry that are significantly smaller than 10 mm (0.4 inches) at birth need to be started on smaller foods that are more difficult to provide in copious amounts on a daily basis, such as rotifers, copepods, and larval Mysis, making them more difficult to raise. Likewise, seahorse fry that undergo an extended pelagic phase, during which they drift freely with the plankton, are much more troublesome to raise than benthic seahorse fry, which orient to the substrate and seek out hitching posts straightaway. The pelagic fry are difficult because the surface huggers tend to gulp air and suffer fatal buoyancy problems, and may even become entrapped by surface tension. As a result, most hobbyists find that mortality is very high during the pelagic phase.
The easiest seahorse fry to rear are therefore benthic fry that are large and well developed at birth. Dwarf seahorses or Pixies (Hippocampus zosterae) fall into this category, and indeed many hobbyists have closed the life cycle with zosterae. The most difficult seahorse fry to raise are relatively small and underdeveloped at birth, and must pass through a lengthy pelagic stage. Brazilian seahorse fry (Hippocampus reidi) are a good example of this category, and are notoriously difficult to raise.
Ocean Riders span the gamut in that regard, including both those species that are the easiest of all to raise and those that are the most difficult to rear, and everything in between. At the one extreme, there are Mo’Olios, which produce very large broods of tiny fry that are barely 3-4 mm at birth and remain pelagic all their lives, even as adults. Mo’Olios are very challenging for even expert aquaculturists with state-of-the-art facilities to raise. Brazileros and Gigantes likewise have enormous broods of relatively small (6-7 mm) fry that undergo a rather protracted pelagic phase lasting weeks. The average hobbyist would still be hard-pressed to regularly raise any of their fry.
At the other extreme, there are Pixies, which produce small broods of large, well-developed benthic fry that hitch from day one. Pixies are probably the easiest seahorses to rear, and no doubt more hobbyists have closed the life cycle with this species than all other seahorses combined. Most of the remaining Ocean Rider types (Mustangs, Sunbursts, Pintos, Fire Reds) produce fry that are fairly good sized (about 8-10 mm) and whose pelagic phase is fairly short (several days rather than weeks), and which are therefore intermediate in difficulty.
Mustangs and Sunburst will produce fry that are moderately difficult to raise. They will be able to eat newly hatched brine shrimp right away, but they will go through a pelagic phase lasting anywhere from several days to a week or two. The link below will take you to an article that discusses how to set up a basic nursery tank, simple feeding regimens, and rearing the fry in greater detail (your Mustang babies are suitable for the "easy" rearing method outlined in the article):
Aside from the very basic nursery setup described in the article, many other ingenious nursery tank designs have been tried to improve the survivorship of pelagic seahorse fry like Mustang babies. The following excerpt from my new book (Complete Guide to Greater Seahorses, TFH Publications) discusses some of these other options:
Nursery Options for Pelagic Fry.
Unfortunately, such simple nurseries are not well suited for seahorse fry that go through a prolonged pelagic period before they settle down to the bottom and seek out hitching posts. Special precautions must be taken to circumvent the surface-hugging behavior of pelagic fry and the problems this presents, and above all, to prevent them from accidentally ingesting air. The planktonic seahorse fry feed at the surface where their prey tends to congregate, drawn to the light, and all too often the newborns take in air along with their food and cannot expel this air. When this happens, it upsets the fry’s equilibrium, and they will float sideways on the surface of the water. Upon close examination of these floaters, a bubble of trapped air can be spotted just below the head (Tracy Warland, pers. com.).
Sadly, such fry are doomed. Once air has been ingested, there is nothing the aquarist can do to save the delicate babies. Therefore, once the newborns have had an initial opportunity to fill their swim bladders, pelagic fry must be kept away from the surface.
Many seahorse breeders have employed ingenious schemes in order to overcome these difficulties when raising pelagic fry. For example, some breeders have tried using mesh enclosures to physically restrain the fry from congregating at the surface. And since the fry and their prey are positively phototactic (attracted to light), other breeders have experimented with nursery tanks that are lit from the side or even the bottom, rather than the top, in the hope that this will draw the newborns away from the surface.
The Shaded Nursery.
The idea behind the shaded nursery is to concentrate the feeding in the lowest portion of the tank, thereby drawing the pelagic fry down to the food supply. This usually accomplished by shading the top 2/3 to 7/8 of the nursery by covering the sides of the tank with black construction paper or applying black duct tape around the circumference of the tank. Strip reflectors turned on their sides are then used to illuminate the uncovered portion at the base of the tank from either side. This concentrates phototactic prey items such as copepods, Artemia nauplii, and larval Mysis near the bottom of the tank, forcing the seahorse fry to come down to feed.
Some hobbyists have taken this concept a step further, and keep darkened nursery tanks on glass-topped tables, lighting them from underneath. Such measures certainly do help, and have increased survivorship in some cases, but success has been limited. Most breeders have now moved beyond bottom-lit nurseries in search of a better solution for rearing pelagic seahorse fry. Various kreisel and pseudokreisel nursery tank designs were the next to be explored, and they still remain very popular today.
Kreisel and Pseudokreisel Nurseries.
Kreisel/pseudokreisel nursery tanks rely on gentle, carefully directed currents to keep pelagic fry — and their food (rotifers, Artemia nauplii, copepods, etc.) — suspended evenly in a circular flow until the young seahorses are ready to settle down on the bottom.
Centripetal force thus draws the fry and their food gently towards the center of this vortex and keeps them suspended in midwater. This has several beneficial effects. Most importantly, it keeps the fry off the surface and prevents them from gulping air. Secondly, it keeps the newborns from swimming into the side glass (in the vastness of the ocean, pelagic fry NEVER encounter such obstacles, and the baffled newborns can injure or exhaust themselves trying to swim through these invisible barriers in an aquarium). And it has the added advantage of concentrating the newborns’ food supply exactly where the hungry fry are drifting.
The kreisel-effect can be accomplished any number of ways, and is generally much easier to achieve than you might imagine. For example, one early kreisel-type design employed a small hexagonal aquarium as a nursery. A hex tank generally has the right height-to-circumference ratio to produce good results and the hexagonal sides approximate a circle, giving it the right shape for a kreisel design. To produce the proper flow, an airlift was positioned in the exact center of the tank, with the lift tube extended so it protruded slightly above the level of the water. The airflow was adjusted so that it lifted the water just enough to spill gently over the top of the tube all the way around. The water would well up over the top of the tube, flow down and outward to the sides of the hex, which would then direct it downwards, across the bottom, and back up at the center of the tank, thus creating a gentle toroidal circulation pattern within the tank. The fry and their food would be suspended and concentrated along the central midline of this torus as a result.
A simpler but equally effective pseudokreisel design uses two very small powerheads positioned at the extreme top of the tank on opposite sides to produce the desired circular flow while providing surface agitation and efficient gas exchange. The two pumps create the swirling pseudokreisel effect that breaks up surface tension, eliminates dead spots at top where pelagic fry otherwise tend to accumulate, and keeps surface-huggers from sticking to the sides of the aquarium (Etling, pers. com.). High tanks rather than the long versions work best for this type of nursery, simply because their dimensions (length-to-width ratio) are better suited for producing the circular flow. Karen Etling has used this type of pseudokreisel nursery to raise extremely challenging Hippocampus reidi fry with impressive results.
Sometimes the most effective pseudokreisel nurseries are also the simplest. One such design uses a bubble wand or air bar positioned tightly against one side of the aquarium to disrupt the surface tension and create a slow, circular current. If the tank is rectangular in shape, the bubble wand should be secured at the bottom of one of the long sides of the aquarium. What could be easier?
Aside from its simplicity, the beauty of this system is its versatility. It can be scaled up to whatever size nursery is required or desired. For example, Jorge A. Gomezjurado used this exact type of pseudokreisel for a 90-gallon nursery at the Steinhart Aquarium, where it proved to be very effective for raising huge broods of pelagic Hippocampus ingens fry. Jorge notes the circular current (the kreisel effect) works well for keeping the fry away from to top and keeps the developing young and their food dispersed uniformly through the nursery tank (Gomezjurado, pers. com.).
A variation on this type of nursery adds drip bars or spray bars positioned just above the water level to create additional surface turbulence. When used in conjunction with the back-mounted bubble wand, the spray bars enhance the effectiveness of the circular flow pattern in nudging the fry away from the surface. This combination of surface agitation plus the kreisel effect is very efficient at preventing pelagic fry from getting stuck to the sides and entrapped by surface tension (Bethany Watson, pers. com.).
Another very simple, inexpensive kreisel design is based on the drum-style, dime-store goldfish bowl. The proper goldfish bowls for this type of nursery have a circular cross-section with a flat front and back for better viewing. A slow trickle of bubbles running up the middle of one of the curved sides creates a top-to-bottom circular current. This is accomplished by bending a length of rigid airline tubing to conform to the arc of the side and gluing it in place at the proper position — exactly midway, front to back, ending up exactly halfway down the side of the goldfish bowl (Marliave, pers. com.). A gentle bubble stream originating at this point will generate the desired kreisel flow pattern. (Bending the flexible tubing to the correct curve or arc is the only tricky part about this design. Flexible airline might work just as well, IF you glue it in place securely so it doesn’t work loose.) Silicone aquarium cement is used to fill in the depression around the inside base, a feature common to all such goldfish bowls, in order to prevent debris from accumulating in this groove (Marliave, pers. com.).
Voila — just like that you have a fully functional, room temperature, static kreisel for raising pelagic seahorse fry! This design was developed by Jeff Marliave at the Vancouver Aquarium Marine Science Centre for conducting experiments with nutrition and diet in seahorse husbandry. These goldfish-bowl nurseries are ideal for this since they allow small kreisel setups to be created easily and economically in quantity, which makes it practical to run multiple kreisel nurseries for replicates testing different experimental treatments (Marliave, pers. com.). Hobbyists will find them equally useful for breaking up large broods into manageable groups dispersed among a number of small nurseries.
A suitable hitching post is secured to bottom, precisely in the middle where it won’t disrupt the circular kreisel flow (Marliave, pers. com.). Jeff finds a piece of hard coral tied to a length of unraveled polypropylene twine works well as a central hitching post. This arrangement allows benthic babies, or juvenile pelagic ponies that have settled, to hitch in the calm space at the center of rotation where there food is concentrated by the currents and an endless parade of perfect prey passes right past their snouts (Marliave, pers. com.). This helps maintain the optimal feeding density and provides maximum feeding opportunities for the rapidly growing young with minimum expenditure of energy on their part. They can eat like little pigs all day long at their leisure without any danger of accidentally ingesting air.
The goldfish-bowl kreisels are also easy to keep clean and to sterilize after use. For proper hygiene and sanitation, Jeff recommends washing them out regularly and air drying them, using spare kreisels to replace the rearing tanks in the meantime. Fecal pellets and dead prey items accumulate under the coral for easy siphoning during daily partial water changes, which maintain water quality in the nurseries (Marliave, pers. com.).
One of the few shortcomings of such goldfish-bowl kreisels is that relatively few fry or juveniles can be raised in each bowl due to the small size of the nursery. This is easily compensated for by the fact that it’s simple to set up and operate many such nurseries simultaneously.
As you can see, there are many different kreisel and pseudokreisel designs, but all such nursery tanks have certain features in common. They all rely on innovative methods that break the surface tension and result in a circular current pattern (the kreisel effect) that keeps the developing fry uniformly suspended in midwater where their food is likewise concentrated. This is very helpful in overcoming many of the difficulties inherent in raising pelagic seahorse fry, and such nurseries have been employed by many home hobbyists with varying degrees of success. It’s a good system and still in widespread use today, but has lately begun to be supplanted by another design with even more flexibility — the in-tank nursery.
The Divided Nursery.
The versatile in-tank nurseries evolved from the basic Divided Nursery tank design, which simply involves separating a standard 10-, 20- or 30-gallon aquarium into two or more different compartments with a common water supply using perforated tank dividers. All of the equipment and filtration goes into one of the resulting compartments while the other compartment(s) serve as the nursery or nurseries for the fry. The perforated barrier allows water to circulate freely between the compartments while acting as a baffle that greatly dampens the turbulence generated on the equipment side.
It is also very effective at keeping newly hatched brine shrimp confined to the fry’s nursery compartment, especially if two of the perforated plastic dividers are positioned side-by-side with a small 1/8-1/4-inch gap between them, forming a double barrier (Abbott, 2003). Sometimes the perforations are covered with plastic window screen or the plastic mesh sold in craft stores for needlepoint projects to increase the effectiveness of the barriers (Abbott, 2003). Many hobbyists also darken the equipment side and position a strip reflector or table lamp at the end of the nursery compartment opposite the filtration side, in order to draw the baby brine shrimp (bbs) away from the tank divider and filters, while concentrating the bbs in a smaller area so the fry can feed more efficiently (Abbott, 2003).
All of the gear is thus isolated on one side of the partition safely away from the fry and their food. The larger volume of water a divided tank provides gives the nursery greater stability as far as fluctuations in temperature and pH go, makes it easier to maintain optimum water quality, and increases your margin for error accordingly (Abbott, 2003). With the tank divided in this way, any sort of mechanical, chemical or biological filtration you care to provide can be safely operated in the equipment area without disturbing the delicate fry in the nursery area (Abbott, 2003). The developing young thus enjoy all the benefits that better filtration and a large water volume can provide, while being confined in a smaller nursery compartment, making it easy to maintain an adequate feeding density (Abbott, 2003).
The divided nursery has proven to be a successful design and hobbyist have developed many variations on this basic theme over the years. In fact, the divided nursery tank was the inspiration for the popular tank-within-a-tank nurseries that were soon to follow.
The In-Tank Nursery.
In-tank nurseries enjoy all the advantages of divided nurseries and then some. For example, like divided nurseries, the tank-within-a-tank design makes it much easier to provide seahorse fry with stable conditions and optimum water quality, vastly increases filtration and equipment options, simplifies maintenance and offers enormous versatility. The idea behind the in-tank nursery is to confine the seahorse fry in a small, flow-through enclosure that can then be attached securely inside a larger aquarium. The in-tank fry enclosure must allow water to pass through it freely but not fry food such as copepods, rotifers or Artemia nauplii. The enclosure thus allows the food to be concentrated in a small space to maintain the proper feeding density, while at the same time providing the fry with all the benefits of living in a much larger volume of water. This includes greater stability in terms of water temp, pH, oxygen levels, salinity and so on.
But by far the biggest advantage of the in-tank nursery is the superior water quality it provides. The larger tanks that accommodate the fry enclosures are normally in the 10-20 gallon range, but there is no upper limit to the size of the host aquarium — the bigger, the better. Of course, for starters, the larger volume of water is naturally more resistant to pollution from the mass consumption and elimination one must deal with when rearing seahorse fry. But more importantly, with the fry safely sheltered in their nursery, the main tank can be equipped with any kind of filtration and filter media you can think of to improve water quality or safeguard the health of the fry. This includes heaters, sponge filters, inside box filters or external power filters with activated carbon, polyfilter pads, or ion-exchange resins, micron-level mechanical filtration, bio-wheels, wet/dry filtration, protein skimmers, UV sterilizers, ozonizers — you name it. Airstones, bubble wands, powerheads, filters and the like can operated full blast without worrying that they’ll buffet the fragile fry or that they filters may ‘eat’ the newborns or consume all their food. Use your imagination — anything goes!
Water quality benefits as a result, and the added filtration reduces the need for frequent water changes. When substantial water changes are called for, the main tank makes the whole process easier.
The first in-tank nurseries were ready-made breeder nets intended for livebearing freshwater tropicals (Abbott, 2003). These breeder nets worked very well for dwarf seahorses, which produce small numbers of babies (Abbott, 2003), but they are not well suited for the huge broods of fry many of the greater seahorses produce. Hobbyists soon began to improvise in order to overcome the limitations of such breeder nets and accommodate larger broods in their fry enclosures. Breeders began to experiment with in-tank refugia, “critter keepers,” and various plastic containers to meet their needs. They modified these by drilling them full of holes and covering the holes with plastic mesh. If necessary, an airline is added to the fry enclosure for better circulation and a drip line brings filtered water in from the main tank or an external power filter.
The versatility of in-tank nurseries is one of their biggest assets. They allow almost any existing aquarium to “host” a fry enclosure and there is also great flexibility in the design of the inner nursery tank. They can easily be modified to accommodate either benthic or pelagic seahorse fry, and multiple in-tank nurseries can be housed in one big main aquarium. Endless variations on this basic concept are possible. The in-tank nursery is simply a much more versatile and adaptable design than the divided nurseries that preceded it.
Liisa Coit is one of the innovative aquarists who have experimented with several different in-tank nursery designs. She is a successful private breeder whom has closed the life cycle with Hippocampus erectus and H. zosterae. Liisa is also an accomplished do-it-yourselfer, and she has raised fourth-generation homegrown erectus in a very efficient nursery that combines the benefits of the best static kreisels with the advantages of in-tank nurseries (Coit, pers. com.).
She uses the plastic drum-style goldfish bowls as the fry enclosures. As with the usual goldfish bowl kreisels, a slow trickle of bubbles running up the middle of one of the curved sides creates the desired top-to-bottom circular current (Coit, pers. com.). This is accomplished by drilling a small hole through the side of the plastic bowl at the proper position — exactly midway, front to back, and precisely halfway down the side of the goldfish bowl. A plastic airline tube connector is glued into the bowl though this hole and plastic airline hosing is attached to the outside from an air pump, allowing a gentle stream of air bubbles to be pumped into the goldfish bowl at that point (Coit, pers. com.). This aerates the bowl and establishes the circular flow (i.e., the kreisel effect). The bubble stream is adjusted so it produces a smooth, gently rotation that keeps the fry suspended evenly at the center of the vortex (Coit, pers. com.).
The plastic goldfish bowls are further modified by drilling 1-1/2” holes near the top, which are then covered with silk screen mesh that is glued over them (Coit, pers. com.). This allows the goldfish-bowl kreisels to be submerged up to the rim within a much larger aquarium, an innovation first built and implemented by David Mulcahy. Liisa find that this design is easier to make and accomplishes the same result as the completely submerged “critter keeper” she originally used as her in-tank fry enclosure.
The goldfish-bowl kreisel nurseries are supported on a shelf that runs the length of the host aquarium they are submerged in (Coit, pers. com.). The shelf is very easy to construct from three pieces of plastic “egg crate” light diffuser, which simply snap together (no glue needed). First the shelf itself is cut to the right length. It should be wide enough to accommodate the goldfish bowls and as long as the host aquarium. Next the two legs are cut to support the shelf. The legs should cut to whatever height is needed to raise the goldfish bowls to the desired water level. The bottom of each leg should be smooth but the ridges should be left on the top of each leg. The long shelf can then be placed on top the legs and the ridges will snap in place (Coit, pers. com.). The entire shelf and the goldfish bowls it supports can be pushed back and forth when performing water changes or cleaning the host tank (Coit, pers. com.). For further stability, plastic electrical ties can be used to fasten the legs to the shelf (Coit, pers. com.).
As with any other in-tank nursery, the large host tank can be equipped with whatever supplemental filtration you desire in order to provide optimum water quality to the fry enclosures. This can include a protein skimmer, ultraviolet sterilizer, or external power filter equipped with bio-balls, polyfilter pads, ammonia absorbers, and the like.
Lengths of airline tubing are used to siphon filtered water from the power filter into each of the goldfish-bowl kreisels (Coit, pers. com.). (Since the goldfish bowls are lower that the level of the water in the external filter, gravity keeps the siphons flowing.)
At feeding time, the siphon tubes feeding filtered water to the bowls are removed so they don’t force the brine shrimp nauplii out through the mesh-covered holes (Coit, pers. com.). This assures that a good feeding density of baby brine shrimp is maintained, concentrated with the fry at the center of the bowl and held in suspension by the circular flow. After the fry have had their fill, the water lines are put back in place and soon flush the excess, uneaten Artemia out of the bowls into the main tank, which facilitates the cleaning of the fry enclosures (Coit, pers. com.).
Coit prefers to keep pelagic fry in the goldfish-bowl, in-tank kreisel nurseries until they begin to hitch and orient themselves toward the bottom. At that point, she transfers them into more spacious “critter keeper” in-tank nurseries for further rearing, and finally into 10-gallon grow-out tanks (Coit, pers. com.). As one example of the versatility of in-tank nurseries, the large host aquariums can do double duty as grow-out tanks for the juveniles as long as all of the filter intakes are screened off.
The Greenwater “Starter” Nursery.
Basically, this system involves giving small numbers of handpicked fry a head start by raising them in a tank with a well-established greenwater culture for the crucial first week or two of their lives. A tank of greenwater is set up in a well-lit area and once the microalgae culture has taken off, it is seeded with copepods or rotifers. The microalgae acts as the filtration, utilizing nitrogenous wastes for growth. The idea is to provide a balanced system in microcosm with a self-sustaining food chain: the phytoplankton (microalgae culture) utilizes sunlight and nitrogenous wastes for growth and helps maintain water quality, while zooplankton (copepods or rotifers) feed on the microalgae and larger predators (seahorse fry) keep the ‘pod population in check. Additional greenwater and/or copepods or rotifers may be added periodically as needed to keep the nursery going.
In actual practice, it is difficult to for the home hobbyist to maintain the proper balance for any length of time before the greenwater culture or the population of copepods (or both) crashes. As a result, greenwater nurseries have limited applications and are useful primarily for the short-term rearing of small numbers of pelagic fry.
However, they can be quite helpful in giving pelagic seahorse fry a badly needed headstart. For example, once the hobbyist has culled a large brood of Hippocampus reidi fry down to a manageable number of the hardiest newborns, they can be introduced to a greenwater nursery where they can fatten up on tiny copepods or rotifers. This can help get the newborns through the first week or two of their lives until they are able to accept first-instar Artemia nauplii and can be transferred to a conventional nursery for further rearing.
The turbidity provided by the greenwater helps keep the phototactic fry evenly dispersed throughout the water column and away from the surface. Jorge Gomezjurado has been very successful rearing Hippocampus reidi and H. ingens fry at the National Aquarium in Baltimore using kreisel nurseries with the proper density of microalgae (i.e., greenwater). Jorge has found that turbidity is an important factor in the juvenile rearing environment for these species and he achieves the proper level of murkiness for optimum results by using algae (Nannochloropsis and Isochrysis) at a concentration of about 100 cells per ml (Bull and Mitchell 2002).
Hyposalinity for Pelagic Nurseries.
Regardless of the type of nursery tank you use, there is one simple measure you can take to counteract the surface-hugging tendency of pelagic fry and increase survivorship during their pelagic phase: raise them at reduced salinity. Keeping the nurseries at a specific gravity of 1.016 (23 ppt salinity) makes the fry less buoyant and thereby reduces problems with surface huggers, entrapment in surface tension and accidentally ingesting air while feeding at the surface.
As an added benefit, reduced salinity also helps prevent parasite problems. Marine parasites need high osmotic pressure externally in order to maintain a normal water balance within their bodies (Kollman, 1998). Reduce the salinity of the surrounding saltwater sufficiently, and water moves via osmosis into the parasites’ bodies until they literally explode (Kollman, 1998). A specific gravity of 1.016 is low enough to provide the fry with a significant measure of protection from parasites in this way.
Hyposalinity is compatible with all types of nurseries. It can be safely employed with shaded or side-lit nurseries, kreisels and pseudokreisels, or divided nurseries and in-tank nurseries. Hippocampus reidi breeders report that reducing the salinity in their fry tanks can reduce mortalities by up to 50% during the high-risk pelagic period (Nicola Strawbridge, pers. com.).
That should give you a few ideas about how to set up a suitable nursery or containment system for your seahorse fry. As you can see, most nurseries or containers for the fry do not have any overflows or filtration systems to suck up the newborns; rather, they rely on daily water changes and siphoning fecal pellets and the three from the bottom of the nursery tanks in order to maintain water quality. Hopefully, one of these nurseries should work well for your needs and interests.
Unless you are keeping Pixies or dwarf seahorses (Hippocampus zosterae), the fry should not be raised in the same tank alongside of their parents. Otherwise it would be too difficult to maintain an adequate feeding density for the fry in the main tank. If you let us know what type of seahorses you are keeping, we can give you a better idea of the type of nursery tank or container that might work best for you.
Best of luck with your prolific ponies!