I don’t know my Seahorses gender.

Dear Charlie:

I’m very sorry to hear about the demise of your Hippocampus comes, sir. That’s a common problem with pet-shop ponies but Tigertails have such beautiful markings I know it must have been very difficult to resist, particularly if the dealer said that it was a pregnant male. All my condolences on your loss!

There is a handy trick for sexing H. kuda seahorses but it only works with the genuine article. True kuda tend to be sexually dimorphic in coloration. Adult females are typically yellow with large dark spots about 2-4 mm in diameter (Mai 2004a). Wolfgang Mai maintains a breeding colony of H. kuda and never observes yellow males with black spots (Mai 2004a). Males often exhibit a grayish-black background coloration with numerous pale lines, overlaid with a pattern of black dots. So if your kuda is yellow with large dark spots, it is very likely a female; if not, then chances are good that you have a male.

I’m not sure how helpful that information will be in your case, however, since you mentioned that your juvenile kuda was changing its coloration a lot, and there are a bunch of different seahorse species masquerading under the name of Hippocampus kuda these days that are nothing of the sort. So let’s cover all of the bases and review how to sex seahorses the conventional way as well, including sexing juveniles by the shape and position of the anal fin.

Ordinarily, one would think that sexing seahorses should be 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.

You can also attempt 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.

Adolescent males will also sometimes show a thick dark line near their vent where their pouch will eventually form as they mature. (This may be the case with your young H. kuda, Charlie, since you mentioned it has a dark line under its belly, in which case you likely have in immature male.)

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 white 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).

Good luck determining the sex of your H. kuda and finding a suitable mate for it, sir! However, before you add anymore seahorses, it would be a wise precaution to wait long enough to be sure that your H. kuda did not contract any kind of a pathogen or parasite from the H. comes that died.

Best wishes with all your fishes, Charlie!

Respectfully,
Pete Giwojna

Dear Charlie:

Okay, that sounds pretty promising — if your juvenile has no dark spots and is beginning to develop a nascent pouch, you can be pretty confident that you have a young male.

It’s certainly is encouraging that he’s eating so well and showing steady growth. If he is eating 100 adult brine shrimp daily, he certainly has a robust appetite. It’s excellent that you are enriching the brine shrimp — that’s the only way to provide good nutritional value with Artemia. By all means, do keep fortifying the brine shrimp for your H. kuda (Vibrance 1 is ideal for this, by the way) and be sure to disinfect it as well.

Brine shrimp are no doubt the most widely used live foods for sea horses. They are convenient, always available, easy to hatch and raise, and adults can be bought by the pint or quart at many fish stores (Giwojna, Oct. 1996).

However, commercially raised brine shrimp have one big drawback. By the time they are purchased and released in the aquarium, they usually have not eaten for several days, and starved brine shrimp are nutritionally barren. It is therefore imperative that brine shrimp be fortified before they are fed to your sea horses. (As discussed earlier, unfortified adult brine shrimp are useful for feeding to captive-bred seahorses on a staple diet of enriched frozen Mysis on their fasting days precisely because the brine shrimp have nonexistent nutritional value.)

Fortunately, brine shrimp are filter feeders and will take in whatever is suspended in the water with them that has a manageable particle size. This can be yeast cells; unicellular algae; rotifers; micronized rice bran, whey, wheat flour, or egg yolk; dried Spirulina algae; water-soluble vitamin and mineral formulations designed for marine fish; or whatever else the aquarist cares to add to their culture water (Daleco Aquarists Supply Manual, 1995).

I recommend using one of the concentrated food additives or enrichment products that have recently been developed specifically for mariculturists. The best additives are rich in lipids, especially highly unsaturated fatty acids (HUFA), and vitamins such as stabilized Vitamin C and cyanocobalmin (B-12) (Giwojna, Oct. 1996). Adding such enrichment products to a 6-ounce portion of brine shrimp, and then allowing at least 12 hours for the shrimp to ingest it can fortify store-bought adult Artemia (Giwojna, Oct. 1996)

Liquid vitamin formulations can also be added, and the ability to enrich their lipid and vitamin content this way allows us to treat brine shrimp as animated vitamin pills for seahorses (Lawrence, 1998). The savvy seahorse keeper should regard enriched Artemia as bio-encapsulated food for his charges and take full advantage of every opportunity to fortify the shrimp (Lawrence, 1998).

However, Charlie, if you’ll be supplementing your seahorse’s diet with adult brine shrimp regularly, there are a few precautions you must be careful to observe. First and foremost, you must be careful to disinfect live food beforehand to assure you won’t be introducing any pathogens or parasites along with the prey items, as discussed below.

There is one potentially serious drawback to feeding your seahorses living prey on a regular basis. There is always the chance that you can introduce disease into your aquarium along the with the live food. Live Artemia (brine shrimp), for example, are known disease vectors for a long laundry list of fish pathogens, and should be treated with caution in that regard – especially if obtained from your local fish store (LFS). The aquarist who relies on live foods for his seahorses MUST take special precautions to eliminate this potential danger!

Fortunately, there are a couple of simple measures that can minimize such risks. Decapsulating Artemia cysts, for instance, removes all known parasites and pathogens, effectively sterilizing brine shrimp eggs. Large public aquaria routinely go a step further, disinfecting live foods by administering a 10-minute freshwater bath and then rinsing it thoroughly through a 100-micron strainer before offering it to their seahorses (Bull and Mitchell 2002). Home hobbyists should do the same (a brine shrimp net will suffice for the strainer). Brine shrimp — the chief offender as a disease vector — tolerate this disinfection process extremely well. In addition, adult brine shrimp (Artemia sp.) are now available from High-Health facilities, which greatly minimizes the risk of disease contamination, and if possible, Sandy, you should take full advantage of these safe vendors when purchasing live foods.

Finally, Charlie, you need to be aware that adult brine shrimp are not suitable as the staple, everyday diet for your seahorses over the long term. It’s fine to provide your seahorses with live adult brine shrimp as an occasional treat, or to use it as a supplement to frozen Mysis several times a week. You can even feed it to your seahorses daily, giving them with one meal a day of live brine shrimp, as long as you also offer them a second feeding with Mysis. But seahorses that are fed a strict diet of adult brine shrimp will eventually developed a debilitating condition known as soft plate disease over time:

Soft Plate Disease:

Seahorses and pipefish that receive a diet deficient in calcium are prone to "soft plate" syndrome, which is a progressive disease characterized by decalcification of the bony plates that fuse together to form the exoskeleton (Greco, 2004). In the olden days, this was often a problem with seahorses that were fed a diet consisting solely of Artemia (Greco, 2004). We now know that brine shrimp (Artemia spp.) contains inadequate levels of calcium and an imbalanced ratio of calcium to phosphorus, making it unsuitable as a staple diet even when enriched (Greco, 2004).

Seahorses afflicted with soft plate syndrome exhibit shortened lifespans, decalcification of their exoskeleton, and poor survival rates amongst their fry (Greco, 2004). Pregnant males face the greatest risk of soft plate. Seahorse fry are known to incorporate calcium provided by their father into their skeletons during their embryonic development, so when a gravid male is deficient in calcium, his rapidly growing offspring typically suffer high mortalities due to a condition akin to rickets in human children.

Fortunately, this debilitating condition is easily prevented by providing seahorses with adequate levels of bioavailable calcium either in their diet or in the aquarium water itself (minerals can be obtained by fish directly from the water; Greco, 2004). I have never heard of a case of soft plate in a seahorse kept in a reef tank that received Kalkwasser (calcium hydroxide) via an automatic doser or regular supplementation of bioavailable calcium. Nor have I even seen this condition in seahorses that received a stable diet of enriched frozen Mysis relicta.

In short, Charlie, don’t hesitate to supplement your seahorse’s diet freely with liberal feedings of adult brine shrimp as long as you enrich the Artemia religiously, disinfect it beforehand, and diversify their diet with hard bodied crustaceans or another good source of bioavailable calcium.

Best of luck with your Hippocampus kuda, sir!

Happy Trails!
Pete Giwojna