Is my new arrival pregnant?

Dear plefton:

Yes, if you ordered a mated pair of Mustangs, it is quite possible that the male could be gravid, although Ocean Rider always tries to avoid shipping seahorses that are obviously pregnant so that the stress of long-distance shipping does not cause any complications.

It is also possible that the male has puffed up his pouch in order to perform pouch displays to entice his female to mate with him, and that’s why his brood pouch appears to be unusually large…

Here is an excerpt from my new book (Complete Guide to Greater Seahorses in the Aquarium, unpublished) that describes the pouch displays performed by courting stallions in more detail:

<Open quote>
Pouch Displays: Pumping and Ballooning.

Pumping and Ballooning are pouch display performed to some extent by all male seahorses regardless of species. The energetic display known as “Pumping” is a vital part of the courtship ritual in all seahorse species that have been studied to date. Temperate and tropical seahorses alike, from the smallest pygmy ponies to the largest of the “giant” species, it appears that all male seahorses perform such pouch displays.

Pumping requires a series of coordinated movements. Bending vigorously, the aroused male jackknifes his tail to meet his trunk, thereby compressing his inflated brood pouch in the middle. The male then straightens up again, suddenly snapping back to “attention” so as to relieve the pressure on his severely compressed midsection. This rapid pumping motion has the effect of forcing water in and out of the brood pouch in a manner that is virtually identical to the way the young are expelled at birth (Vincent, 1990).

The strenuous pumping action is the stallion’s way of demonstrating his pouch is empty of eggs and that he is a strong, healthy, vigorous specimen capable of carrying countless eggs (Vincent, 1990). By so doing, he assures the female that he is ready, willing, and able to mate, and that he can successfully carry and deliver her entire brood.

The energetic pumping also helps prepare the male’s brood pouch for pregnancy. It flushes and cleanses out the interior of the marsupium, helps increase the blood supply to the lining of the pouch, and expands the elastic pouch to its fullest extent, in order to prepare it to receive a new batch of eggs. This flushing action is also believed to release special chemicals called pheromones and waft them towards the nearby female to stimulate her all the more. The hormone prolactin is probably the most important of these chemical triggers.

Courtship in many temperate and subtemperate seahorses is dominated by such pouch displays. In addition to pumping, these cold-water ponies also engage in a different type of pouch display known as “Ballooning.” This is a simple display in which they inflate their brood pouches to the fullest possible extent and parade around in front of the female in all their glory as though trying to impress her with the sheer dimensions of their pouches. The pumped up paramours perform proudly, putting on quite a show for the flirtatious fillies. (All you ladies out there are surely all too familiar with this act. No doubt you attract the same sort of attention and elicit the same type of behavior every summer at muscle beach, where all the macho men pump up their biceps, suck in their guts, and throw out their chests whenever you stroll past.)

Often all the males in the vicinity will compete for the attention of the same female, chasing after her with their pouches fully inflated this way. When all the boys are in full-blown pursuit of a female ripe with eggs, they look like a flotilla of hot air balloons racing to the finish line.

Hippocampus abdominalis, H. breviceps, and H. tuberculatus, in particular, have developed enormous pouches that are all out of proportion to their bodies when fully expanded. Their oversized pouches look like over-inflated balloons ready to burst when these stallions come a courting. Take the tiny Hippocampus breviceps, for example. With its brood pouch expanded to the maximum, a courting male looks like a fuzzy 3-inch pipe cleaner that swallowed a golf ball! Courtship in temperate/subtemperate species generally centers around pouch displays more than color changes, dancing or prancing.

Pumping is one of the final stages of courtship and it indicates the seahorses are really getting serious (Vincent, 1990). Mating will take place shortly, as soon as the female hydrates her eggs, unless something intervenes in the interim.
<Close quote>

Okay, plefton, that’s the story on the pouch displays males perform to stretch and expand their elastic brood pouch in preparation for breeding. When it’s not inflated with water (or filled with a brood of embryonic young), the pouch may be loose and flaccid at such times.

In fact, when males are not actively breeding, their pouches can actually shrink to the point that it is difficult to determine their gender. 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 brood 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.

To sum up, plefton, it sounds like either your new Mustang stallion may be pregnant or that he is trying hard to entice the female to mate with him so that he can get pregnant. That is to be expected when you when you order a mated pair of ponies.

Best wishes with all your fishes!

Happy Trails & Happy Holidays!
Pete Giwojna, Ocean Rider Tech Support