Male or Female

Dear Adam:

Okay, sir, I can understand your dilemma and I would be happy to take a stab at sexing your new Sunbursts from the photographs at the link you provided.

But please bear in mind that I don’t consider myself an expert in that regard – far from it (in fact, I’ve come to the conclusion that I am pretty hapless when it comes to sexing juvenile seahorses) – but I have done my share of breeding and I have seen more than my share of seahorses in my time, so I can determine gender in the mature individuals pretty well…

First of all, let me say that you are the proud owner of a magnificent pair of Sunbursts regardless of their gender. They both have splendid coloration – a golden yellow and a bright orange respectively – and they appear to be in top condition, at the very peak of good health. Glorious!

Secondly, it sounds like your friend is attempting to sex your new ponies according to the angle at which the belly of the seahorse sweeps back to meet the tail. As you know, in females this tends to be more of a right angle (more perpendicular) – forming the “bump on their belly,” as you described it in your e-mail, sir – whereas it tends to form a diagonal in mature males due to the presence of the brood pouch. And that is a tried-and-true method of sexing adult seahorses that are fully mature in most instances…

However, it is not always reliable. For instance, it is a useless technique when attempting to sex juvenile or subadult seahorses, in which the prepubescent males have yet to develop any indications of a brood pouch. And it’s also unreliable when the seahorses are not actively breeding, since the brood pouch of the males shrinks dramatically and becomes much less obvious in the off-season, due to the lack of hormones that are required to sustain the placenta-like changes that prepare the marsupium for breeding. So male seahorses may lack an obvious brood pouch during the off-season when they are no longer breeding. (This is especially true of virgin males, who have yet carry their first brood of babies.)

So looking for a belly bump or judging the sex of the seahorse from the angle its abdomen meets its tail is most helpful when the seahorses are fully mature adults that are actively breeding. In this case, the breeding season for Hippocampus erectus, such as Ocean Rider Mustangs and Sunbursts, is the late spring and summer months when the day length and warmer water temperatures stimulate breeding. In the wild, they breeding season grinds to a halt during the late fall and winter when the cooler water temperatures and shortened daylength no longer produced normal levels of gonadotropin. In other words, the month of December is a time of year when the brood pouch will be much less evident in male seahorses, especially the virgin males and newly mature young adults…

So you must also consider the position of the anal fin in order to accurately determine gender when it’s not the breeding season for your seahorses, or when they are young adults that have not yet begun actively breeding. Due to anatomical differences between the sexes, the anal fin tends to be located higher up on the abdomen of the stallions, in order to allow for the presence of the brood pouch, whereas the anal fin is located lower on the abdomen (i.e., closer to the tail) in female seahorses. As a result, the anal fin typically points downward in the fillies, but the anal fin and males often points outwards (horizontally) in the stallions, or is carried or held at a diagonal angle in the boys…

Looking at the photograph of Link (the larger golden yellow Sunburst), it appears that the anal fin of the seahorse is located higher up on the abdomen and is protruding outwards horizontally, rather than being directed downwards. That makes me suspect that Link may be a young male that simply lacks an obvious brood pouch at this time, Adam.

I could not make out the anal fin in the photos of the smaller bright orange Sunburst you named Zelda as clearly, sir, but from what I can see the anal fin seems to be located lower on the abdomen closer to the tail of the orange individual, and appears to be directed downwards rather than carried horizontally (or at an angle). And that makes me think that Zelda may be a young female.

At any rate, that’s my best guess, judging from the pictures, Adam. In any case, time will tell the tale. Your new Sunbursts will be fully mature by the time Spring rolls around, sir, and with the onset of the breeding season, the hormonal balance of the seahorses will change, and the male’s brood pouch will undergo a period of rapid development that makes it difficult to missr, so everything will become crystal clear with the passage of time.

In the meantime, this is what I normally advise home hobbyists regarding sexing their seahorses:

You would think that sexing seahorses is a snap — pouch, it’s a male; no pouch, it’s a female. But it’s rarely that easy in real life. For instance, it is notoriously difficult to sex juvenile and subadult seahorses, and virgin males that are not yet in breeding condition are frequently mistaken for females, as we’ll discuss below in greater detail.

Sexing Seahorses

Sexing adult, fully mature seahorses in breeding condition is normally simple and straightforward — the males have a brood pouch slung under their abdomens at the base of their tails and the females do not. This difference will be most obvious when the seahorses are courting and breeding, since the stallions perform vigorous pouch displays in which they inflate their pouches with water to the bursting point, making them unmistakable.

However, in actual practice, things are often more confusing, especially when attempting to sex immature (subadult) seahorses or mature seahorses that are not actively breeding. A myriad factors can confound the issue. For example, some fully functional females possess a pseudo-pouch and in some stallions, especially virgin males, the brood pouch shrinks away to almost nothing in the off season when their hormones stop flowing, becoming all but unnoticeable. And late bloomers are always problematic.

In some seahorse species, adult males and females can be very difficult to tell apart when they are not breeding because the male’s pouch shrinks to almost nothing in the offseason and does not become obvious again until hormonal changes triggered by courtship and mating cause it to grow and expand (Bull and Mitchell, 2002).

For example, this is how Michael Payne (Seahorse Sanctuary) describes this phenomenon:

“Temperature may effect whether or not you can see the pouch of a male. In H. breviceps, it is very difficult to sex adults that are not in breeding condition. At low temperatures (17°C), the males’ pouch deflates such that you can hardly see it. Increase the temp (22°C) and the pouch appears and mating starts.”

During the breeding season, the male’s brood pouch undergoes elaborate changes to prepare it for pregnancy. 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 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).

In the offseason, the levels of gonadotropin, testosterone and adrenal corticoids in the bloodstream are reduced, and the pouch deflates and shrinks accordingly, reversing these placenta-like changes. The male’s marsupium becomes much less conspicuous at this time as a result.

It’s possible to sex immature seahorses with no indications of an incipient pouch using the position of the anal fin and a few other subtle indicators as a guide, but the younger the seahorses are the more difficult this is to accomplish with any degree of accuracy. Suffice it to say, sexing juvenile seahorses that are much younger than 5 months can be a very challenging adventure. This is typically done by noting the position and shape of the anal fin as well as the curvature of the abdomen. In immature females, the anal fin is situated right at the very base of the abdomen where it meets the tail and points more or less straight downward, almost flush up against the tail. In immature males that lack a brood pouch, the anal fin is located higher up on the abdomen, allowing room for the brood pouch to subsequently develop, and protrudes outward at an angle from the tail. This makes it appear as if there is more space between the tail and anal fin in juvenile males.

The difference in the position of the anal fin is due to the way the vent is situated in males and females. The seahorse’s vent is the cleft formed by the combined openings of the anus and urogenital pore (Seahorse Anatomy, 2004). It is the simple recessed passage located just above (cranial to) the anal fin in females; in males, the anal fin is located in the middle of the vent where it separates the anal opening from the urogenital pore. The male’s anus is therefore situated above the anal fin while the genital opening of the male is located below the anal fin at the mouth of the brood pouch. In females, however, both the anus and the urogenital pore are located above the anal fin. The presence of the brood pouch makes the anal fin less conspicuous in males, whereas the anal fin is often more obvious on females.

Adolescent males will also sometimes show a thick dark line near their vent where their pouch will eventually form as they mature.

There is also a noticeable difference in the profile of the abdomen. In females, the abdomen curves inward more sharply, so that the base of the belly almost forms a right angle to the tail. In males, the abdomen slopes inward toward the tail more gently, giving the base of the belly a more rounded appearance in profile. In addition, in some species, the anal fin tends to be pointed in females and rounded in males. One can attempt to sex adolescents or even seahorse fry according to these subtle differences, but the younger the specimen, the more likely mistakes are to be made and the greater the chances that the gender that is assigned will prove to be wrong.

The position of the anal fin is thus a fairly good indicator, but it takes a great deal of experience to become proficient at sexing young seahorses this way, and I must confess that I’m pretty lousy at it. I’ve come to the conclusion that it’s really more of an art form than an exact science, and that there’s definitely more than a little intuition involved; I guess I just don’t have the best “feel” for it.

Further confounding the issue of gender is the fact that a certain percentage of females also have a subanal structure that can be easily mistaken for an incipient pouch (Vincent, 1990). This is misleading because the pseudo-pouch seen on many such females is merely a pigmented patch of skin, not a functional brood pouch or even a pocket of tissue (Vincent, 1990). Although they are very often presumed to be male, at least initially, females having these subanal structures produce viable eggs, pair off with males, and mate normally just like all the other fillies.

Mustangs and Sunbursts (Hippocampus erectus) are usually shipped around the age of 5-7 months, which is about when they begin to hit sexual maturity and pair off with one another. But there is considerable variation in that regard — some precocious ponies begin to show pouch development at the tender age of 3-4 months while at the opposite end of the spectrum there may be a few late bloomers that may not develop fully functional pouches until they’re yearlings.

It’s like puberty in humans; some youngsters begin to develop while they’re still in elementary school but others don’t hit puberty until after high school. Most are somewhere in between.

Sexing such late bloomers is always problematic. As I said, the greater seahorses typically reach sexual maturity around the age of 4-6 months (Warland, 2003), so it’s natural to assume that a 6-month seahorse that lacks an obvious brood pouch is a female. Many hobbyists are therefore very surprised when a specimen they were quite certain was female suddenly develops a full-blown pouch at the age of 9-12 months. On the other hand, it’s only natural to assume that a 6-month old seahorse with a subanal patch of skin that’s colored entirely different from the rest of its abdomen is blossoming into a fine young stallion right on schedule, and it can thus be a bit of a shock to hobbyists when their presumed male drops its first clutch of eggs. More than a few aquarists have ended up renaming their seahorses when it became clear that Victoria was actually a Victor (or vice versa).

Okay, that’s the quick rundown on sexing seahorses, sir. Ocean Rider ships out hundreds of seahorses every week, and on rare occasion mistakes are made when assigning gender, which is understandable given the uncertainty of the task and the large number of ponies involved.

But I should point out that when such mistakes occur, it is usually always a young seahorse that was presumed to be female but that eventually turns out to be a late-blooming male, rather than a young stallion that is mistaken for a female…

I suspect that you have a young male and female Sunburst which merely have no interest in breeding right now because of the time of year, Adam, but that’s just an educated guess on my behalf.

Best of luck with your seahorses, Adam! Rest assured that the stallions and fillies have no trouble at all determining the gender of their prospective partners even when we find it difficult to tell the boys from the girls. Seahorses are a great deal better at determining the sex of their tankmates than their keepers are thanks to the chemical cues or pheromones they can detect, and subadult males and females often begin pairing up well before there are obvious external differences in the sexes.

Happy Trails!
Pete Giwojna

And, of course, once we begin, I will be working with you personally every step of the way through our ongoing correspondence until your new aquarium is ready for seahorses and you are well prepared to give them the best of care, regardless of how long that may take.

Dear Adam:

You’re very welcome, sir!

Yeah, my inclination is that you have a young pair (male and female) of Sunbursts, Adam.

Short of waiting until the spring, the easiest way to verify the gender of the seahorses would be for you to take a close look at their anal fins. If the anal fins appear to be situated differently on the two seahorses, then you can be confident that they are of opposite sexes.

If the anal fin is located higher up on the abdomen of one of the seahorses (a male trait) and located lower on the abdomen of the other seahorse, closer to the base of the tail (a female trait), that usually a pretty good indicator of gender.

In addition, fillies tend to carry their anal fin oriented downwards, parallel with the tail (i.e., pointing downward when the seahorse is hitched in its normal upright posture), whereas stallions tend to carry their anal fin extended outwards, away from their abdomens (parallel to the bottom of the aquarium, when the seahorse is hitched it is normal upright position), or at least at an angle, rather than pointing straight downwards.

The difference in the position and typical orientation of the anal fin in males and females is due to anatomical differences in their plumbing and the way it branches to form a separate anus and urogenital pore within the vent – differences which subsequently dictate where the anal fin develops in the different sexes. This makes the position and orientation of the anal fin a fairly reliable indicator of gender, even in juvenile seahorses lacking a distinct pouch.

So in a nutshell, sir, if the anal fin is located differently in both of the Sunbursts, there is a good chance that they are different sexes.

Best of luck with your new arrivals, Adam!

Respectfully,
Pete Giwojna, Ocean Rider Tech Support

Hi Peter,

Do you ship to the uk,if so how much do you charge for a pair of erectus.

Thanks

Sue