Re:seahorse life span

#2658
Pete Giwojna
Guest

Dear Amanda:

You’re very welcome! Okay, if your seahorses are Hippocampus reidi, you should be able to find a mate for your unpaired seahorse without too much difficulty. Brazilian seahorses (H. reidi) are very popular and captive-bread-and-raised specimens are available from several different sources in the US. For example, Ocean Rider offers both yellow Brazileros (H. reidi) and red Brazileros (which are usually bright orange).

Yes, the male with the swollen brood pouch you thought was expecting may simply have been inflating his pouch with water, or he may indeed have been pregnant only to have something disrupt the pregnancy.

As you know, male seahorses perform pouch displays known as "Pumping" and "Ballooning" when they are courting during which they inflate their pouches with water.
Ballooning is a simple display in which courting males fill their brood pouches with water 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.

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.

However, ballooning is much more common in temperate seahorses than tropical species, Amanda. If your male is a Brazilian seahorse (H. reidi) or any other tropical species of seahorse, which is almost certain, then he is much more likely to be engaging in a different type of pouch display known as "Pumping" instead.

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 male’s marsupium also becomes grossly distended during displays of Pumping, but in that case, it is obvious the male is courting because it looks like he’s doing abdominal crunches as the vigorously pumps water in and out of his brood pouch.

During displays of Ballooning and Pumping, the male’s pouch is inflated with seawater, so he maintains neutral buoyancy and can swim normally. As a rule, males don’t perform these pouch displays if they are pregnant. The intrusion of saltwater into the pouch can be harmful to the embryonic young in the early stages of pregnancy because it dilutes or displaces the marsupial fluid that is bathing the fetal fry, and opening the pouch in the later stages of pregnancy is equally disastrous since it may result in the expulsion of pug-nosed preemies still attached to yolk sacs. Ordinarily, once a male seals the aperture of his pouch after the transfer of the eggs, he will not open it again until the hormone isotocin triggers parturition and the birth spasms. So if your male with the enormous pouch has merely been performing displays of Ballooning or Pumping, then he was not actually pregnant, just trying to entice one of your females to mate with him so that he could become pregnant.

On the other hand, Amanda, it’s quite possible that the male with the distended pouch could have been pregnant but that something has interrupted the normal course of the pregnancy and caused him to resorb the eggs and fetal fry. When that happens, hobbyists often describe the phenomenon as a phantom pregnancy or a false pregnancy.

A "phantom pregnancy" is not an altogether uncommon phenomenon with seahorses in the aquarium. In seahorses, a hormone known as fish isotocin, which is the equivalent of oxytocin in mammals, triggers parturition or giving birth (Vincent, 1990). Thus anything that stimulates excess secretion of isotocin can result in premature births, whereas anything which decreases or delays the secretion of isotocin can postpone delivery and prolong a pregnancy abnormally. In a similar manner, disruption of other hormones can cause a male to spontaneously abort a pregnancy or to actually resorb the eggs. The placenta-like changes that take place in brood pouch, the development of the young, and the pregnancy itself are all controlled by various hormones — testosterone, adrenal corticoids, prolactin, and isotocin (Vincent, 1990) — so basically anything that influences the secretion of those key hormones can have a profound effect on the pregnancy.

Some of the factors that influence these hormonal responses are the presence of the female, low oxygen levels, heat stress, and diet. The presence of the female most definitely influences the gestation and brood success of her mate. Numerous studies indicate that the presence of female fishes visually or hormonally stimulates male sexual activity such as courtship, nest building, and the development of androgen-dependent sexual characteristics (Vincent, 1990). Research has also shown conclusively that male seahorses which have been with the same female for more than one mating cycle are markedly more successful in brooding young (Vincent, 1990). It is believed that one of the reasons for this is that the presence of their mate stimulates the secretion of the corticoids (steroid hormones produced by the adrenal cortex) and prolactin that control the pouch environment and maintain the incubation (Vincent, 1990). The male is thought to further expand his pouch and develop the placenta-like internal structures to a greater degree as a result (Giwojna, Feb. 2002). More of the eggs can then be successfully implanted and carried to full term (Giwojna, Feb. 2002). Separating a gravid male from his mate can therefore have a negative impact on his pregnancy and should be strictly avoided.

Low oxygen levels during pregnancy can likewise be disastrous. They result in respiratory distress for the gravid male, putting the embryonic young at risk, as well as directly altering the hormones we have been discussing, which can further disrupt the pregnancy.

Heat stress is doubly bad news for gravid males. Not only can abnormally warm temperatures disrupt the secretion of these key hormones and shut down breeding, they can also directly denature long chain polymers and macromolecules (e.g., proteins, enzymes and hormones) by altering certain bonds and changing the three-dimensional shape of the molecule on the atomic level. And, of course, water temperature also directly affect the metabolism of the seahorse and therefore its gestation period. Up to a certain point, increasing water temperatures will shorten the normal gestation period, just as decreasing water temperature will prolong or extend gestation.

Past a certain point, however, when the increasing temperatures exceed the comfort range for the seahorses, elevated temperatures will bring reproduction to an abrupt halt. For example, the Mexican population of H. ingens begins breeding in late September when the water temperatures decreases below 81°F (27°C), and keep breeding until late May when the water temperatures increase above 80°F again (Eliezer Zúñiga, pers. comm.).

An inadequate diet can also be detrimental to a gravid male for obvious reasons. Maintaining a large brood of developing young can be a big drain on the male’s bodily resources, and a nutritious diet rich in HUFA and essential fatty acids is necessary at this time to help the male keep up his strength. That is why male seahorses have an intestinal tract that’s 50% longer than that of females (Tamaru, Aug. 2001). They need the extra food absorption ability and digestion a longer intestine provides in order to sustain the metabolic demands of up to 1600 rapidly growing fry.

When factors such as these disrupt the pregnancy, it’s not so much a case of "false pregnancy" as a failed pregnancy — a gravid male that was not able to carry his brood of embryonic young and fetal fry to full term due to the sorts of developments we have been discussing. This is how Carol Cozzi-Schmarr describes the situation: "If… conditions are not optimum and the general stress level of the male is too high, the male will simply re-absorb the eggs or abort them. You will sadly think that he was never really pregnant."

It’s possible something like that may have happened with your male that appeared to be pregnant for a couple of weeks, although ultimately nothing came to fruition, Amanda.

Best of luck finding another H. reidi mate for your seahorses, Amanda!

Happy Trails!
Pete Giwojna


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