Pete Giwojna

Dear Sean:

Yes, sir, I recall our previous discussions very well and I can certainly understand your frustration. Your case is very unusual in that you seem to be doing everything properly, your seahorses are thriving, they court and perform the morning greeting ritual, indicating they have pair bonded, and they have mated in your aquarium and successfully accomplished the transfer of eggs on at least two occasions within the past year. Yet on both occasions your stallion has been unable to complete the gestation and deliver a brood of young. Rather, he has purged the eggs from his marsupium within a few days after mating, which is something I had never heard of before and that is normally not even possible, to the best of my knowledge. We have already discussed the factors that influence gestation and can disrupt a pregnancy in some detail on this forum, and I’ll be darned if I can identify anything you are doing wrong or any unfavorable environmental conditions with your seahorse setup that could be triggering such a problem.

Since something appears to go wrong early in the pregnancy when the fertilized eggs would normally be implanting in the wall of the marsupium, let’s review how all of this ordinarily takes place during a normal pregnancy, Sean.

As you know very well by now, sir, male seahorses nourish the developing young in a special brood pouch. Often called the marsupium, this remarkable organ is much more than a simple sack or protective pocket or a mere incubator for the eggs. Think of it as an external womb, which undergoes placenta-like changes throughout the pregnancy in order to meet the needs of the fetal fry. Its internal architecture is surprisingly complex. In fact, the male must begin preparing his pouch to receive his next brood long before gestation begins (Vincent, 1990). The elaboration of the internal pouch anatomy that is necessary to support the developing young is triggered by the male hormone testosterone. The development of these structures is thus under testicular control and takes place primarily in the offseason when the seahorse is not breeding (Vincent, 1990). The four layers of tissue that comprise the pouch undergo increased vascularization at this time (Vincent, 1990) and a longitudinal wall of tissue or septum grows up the middle of the pouch, separating it into left and right halves. This increases the surface area in which fertilized eggs can implant, and enriches the blood supply to the lining of the pouch in which they will imbed. Just before mating occurs, this is enhanced by a surge in the active proliferation of the epithelial tissue that forms the innermost layer of the pouch (Vincent, 1990).

These placenta-like changes accelerate after the actual mating and transfer of the eggs take place. The male releases his sperm as the eggs are deposited. The moment the last egg is nestled safely inside, the male’s pouch deflates, compressing the eggs against the pouch lining in order to facilitate implantation. The male then perches and attempts to settle the eggs properly in his pouch, often undergoing a series of agitated contortions, swaying, twitching, or wagging his tail from side to side, and perhaps stretching as though trying to rearrange the eggs more comfortably (Vincent, 1990). He is dispersing the eggs uniformly throughout his pouch, giving each one the best chance to be fertilized and implant in the septum or wall of the marsupium. The fertile eggs implant in the wall or septum of the pouch, triggering a spongelike expansion of its tissues as the capillaries and blood vessels swell and multiply. Epithelial and connective tissue proliferate around the embedded eggs, enveloping each ovum within a tiny chamber or alveolus of its own (Vincent, 1990). Eventually 7/8 of every embryonic sac is embedded in the spongy tissue lining the pouch (Vincent, 1990). Each compartment or alveolus opens into the central cavity of the pouch. About 1/8 of each embryo remains exposed, protruding through this opening, and is immersed in a special placental fluid within the pouch (Vincent, 1990).

In this way, the brood pouch is prepared to maintain the pregnancy by carrying out the following vital functions:

(1) Protection. The brood pouch protects the young in a number of ways. It shields them from harmful ultraviolet radiation, which can destroy unprotected eggs and larvae (Vincent, 1990). It shelters the eggs and fetal fry from predators, and protects them from siltation and suffocating algae (Vincent, 1990).
(2) Aeration. A dense network of capillaries forms in the connective tissue that surrounds each of the embedded eggs, delivering oxygen to the fetal fry through the membrane of the embryonic sac (Vincent, 1990) and carrying away their metabolic wastes in the same manner.
(3) Control of osmotic pressure. The sealed pouch creates a watertight environment for the developing young and, over the course of the gestation, the male adjusts the osmotic pressure from that of his bodily fluids to that of seawater (Vincent, 1990). The young are thus gradually acclimated to full-strength saltwater over the course of the pregnancy, so the newborns will be right at home when they are expelled from the pouch. This is crucial for the survival of the delicate fry, since sudden changes in osmotic pressure are known to cause stunting, breathing abnormalities, and physical deformities in teleost fish larvae (Vincent, 1990).
(4) Nourishment. A portion of each embryonic sac is bathed within a nourishing placental fluid containing calcium and other inorganic ions contributed by the male (Vincent, 1990). The placental fluid also contains organic ions derived from the female via the yolk. The male secretes enzymes that dissolve away the outer covering of the eggs known as the chorion shortly after incubation begins (any infertile eggs that fail to implant are normally resorbed in the same manner), and the organic ions thus contributed by the female diffuse across the exposed membrane of the embryonic sac into the pouch fluid (Vincent, 1990). There the inorganic ions are transformed into amino acids by a special enzyme (protease) secreted by the pouch epithelium (Vincent, 1990). These amino acids eventually become proteins incorporated within the embryos (Vincent, 1990). The calcium provided by the male is similarly taken up by the embryos and infused into their skeletons (Vincent, 1990).

In short, the brood pouch enfolds, protects, aerates, osmoregulates, and nourishes the developing embryos as the male undergoes a true pregnancy (Vincent, 1990). After the fertilized eggs implant in the walls of the marsupium, the normally soft, flaccid pouch firms up and often darkens in coloration due to the placentalike changes taking place within. And as the embryonic young and fetal fry grow and develop, the pouch typically becomes increasingly distended as the pregnancy progresses, especially when the stallion is carrying a large brood of young.

With that in mind, it’s difficult to understand what is happening with your male, Sean. After mating, any infertile eggs that fail to implant are normally resorbed (the yolk-rich ova are a valuable source of nutrients), rather than expelled. And the fertile eggs implant in the walls of the marsupium and are quickly enveloped and surrounded by vascular-rich tissue, forming an alveolus around each egg, as described above. With the aperture of the pouch tightly closed (the sphincter muscle makes an airtight/watertight seal) and the eggs at least partially embedded, I wouldn’t think the male would be able to eject them even if he were so inclined. Yet that’s exactly what seems to be happening in your case and it has me baffled. I am entering uncharted water here, sir, and running out of anything further to suggest.

Here’s what I think, for whatever it’s worth. You obviously have a healthy pair of seahorses that have pair bonded and are dutifully performing the morning greeting ritual each day, which strengthens and sustains their bond and keeps them physiologically synchronized with one another to facilitate mating. The pair has successfully completed the copulatory rise and transfer of the eggs at least twice within the past year, so we know they are compatible and capable of mating in your aquarium. But this time of year is the off-season for mating in Hippocampus erectus, so the lack of breeding at the moment could be due to seasonal factors, as discussed below.


In the wild, both temperate and tropical seahorses breed best during the summer months and typically take a break from breeding during the offseason. Breeding may therefore naturally tape are off and grind to a halt in late fall and winter, and with wild seahorses in particular, many times there is nothing nothing’s wrong but the calendar when a mated pair fails to reproduce. Even captive-bred seahorses sometimes experience a lull in the festivities at this time of year. That’s just their natural breeding cycle, the rhythm of life built into their genes. There is a good chance that with the return of springtime, your seahorses’ fancy will once again turn to thoughts of love.

I would be patient a little longer and see if your pair of seahorses don’t decide to set up housekeeping again this Spring, Sean. They are obviously healthy and content, and seem to find the conditions in your seahorses tank very much to their liking. Let’s see if the return of warm weather and longer days doesn’t get their hormones flowing again and trigger another mating attempt or two. If not, if they still don’t get serious about mating and rise for another egg transfer — or if they successfully complete the egg transfer but the male is once again unable to carry the pregnancy full-term — then it might be time to consider shaking things up by introducing some new blood.

When your seahorses consistently fail to reproduce despite your best efforts, there is one sure cure that seldom fails to put your breeders back on the fast track: simply add a new bachelor/bachelorette or two to the mix! Adding some fresh blood will almost always trigger a flurry of renewed activity and greetings as the seahorses reassess their shifting social dynamics and check out their prospective new partners (Giwojna, Jan. 1999). As an added bonus, the newcomers increase the genetic diversity of your herd and help prevent inbreeding, strengthening your seahorse’s gene pool.

The mere presence of a potential new rival (or rivals) will often stimulate the reluctant seahorses’ interest in courtship (Giwojna, Jan. 1999). Under such circumstances, just occasionally, seahorses may even end up bonding with partners they had formally rejected (Giwojna, Jan. 1999). It’s funny how an old beau can suddenly seem more attractive when your rival shows an interest in him.

Incompatibility is a much greater problem with wild seahorses than it is with gregarious farm-raised specimens. Captive-bred seahorses are simply not that picky when it comes to selecting mates. Put enough captive-bred Casanovas and frisky farmed-raised fillies together under favorable conditions, and the sparks are sure to fly!

Either way, whether it’s new pairings forming or former rejects reuniting, you can expect renewed interest in courtship and mating to result and your seahorses should soon reward your efforts with lots of breeding and babies.

So if your aquarium is large enough, Sean, and your pair of seahorses has still not produced a healthy brood for you after Spring has come and gone, you might consider introducing a new erectus to your seahorses tank. I’m thinking a new stud may be the way to go, since your female has no trouble producing eggs and your stallion seems to be unwilling or unable to incubate them properly, but this is a new problem for me and I really have no idea what might be wrong.

Or, if you are really eager to have some babies, you could even consider ordering a pregnant male H. erectus, sir, but this would mean ordering a new pair of ponies. In order to obtain a pregnant male you have to order a mated pair and then specify in the "comments" section of the online order form that you want the male to be pregnant. Ocean Rider will then select a mated pair for you in which the male is already gravid when they pack your order for shipping. There is an extra charge of for a pregnant male (about $40 as I recall, the last time I checked), which will be added on to the cost of your order.

Ocean Rider’s policy is only to sell pregnant males as part of a mated pair because it is stressful and cruel to separate pair-bonded seahorses from their mates.

That’s all I can think of at this point, Sean, and I know it’s probably not all that helpful. But under these unusual circumstances, I’m fresh out of likely solutions, short of waiting for the next breeding season to stimulate things and then adding some new blood, if necessary.

Best wishes with all your fishes, sir! Here’s hoping that you have many broods of healthy babies before long, one way or another.

Pete Giwojna

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