Botched Pregnancy???

Dear Sean:

I’m sorry to hear about the complication that arose with your Mustang’s pregnancy, sir. As you know, gestation for Mustangs and Sunbursts (Hippocampus erectus) ranges from 14-30 days, as determined largely by water temperature, and with the chiller on your aquarium keeping things relatively cool, those 12-day embryos that were ejected certainly had not "cooked" enough yet. They definitely needed more incubation time in the oven before they were done developing.

But I don’t think that necessarily means the rest of his brood is going to emerge half-baked or that they are all destined to become deformed preemies. I would liken what has happened with your male to the situation when a gravid stallion spits out one or two, or a few, of the newborns prematurely a day or two ahead of the rest of the brood. It is not that unusual for a gravid male to release a fraction of his brood a bit prematurely, only to shut down operations temporarily and then deliver the rest of the young normally a few days later. When that’s the case, the remainder of the brood is typically released en masse 2-4 days after the first batch of fry were expelled.

So the rest of the embryonic young and fetal fry are not necessarily doomed in your case, Sean. Just don’t do anything to unduly stress your pregnant Mustang and chances are everything will work out well in the long run. Some of the things that influences the gestation period in seahorses and that can disrupt the pregnancy, or even cause a pregnancy to be aborted, in some cases, are discussed below.

To begin with the basics, gestation in seahorses is largely determined by water temperature, is controlled by the levels of key hormones, and can be influenced to a lesser degree by diet and nutrition.

In general, the warmer the water the shorter the gestation period, and vice versa. Relatively cool water temperatures are generally desirable during pregnancy, since they prolong the incubation period and the newborns are larger and better developed when they are subsequently born.

Aside from water temperature, gestation may vary due to hormonal influences as well. For example, in seahorses, a hormone known as fish isotocin, which is the equivalent of oxytocin in mammals, triggers parturition or giving birth. 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 embryonic young, and the pregnancy itself are all controlled by various hormones — testosterone, adrenal corticoids, prolactin, and isotocin — 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, diet and, of course, stress. 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.

Poor water quality — especially ammonia and/or nitrite spikes — are one of the most common aquarium stressors that can disrupt hormones and interrupt a pregnancy. Stress hormones such as cortisol will be released in response to such stressors, at the expense of other adrenal hormones, which can have a negative impact on the pregnancy and the developing fry.

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.

So the actions of the aquarist and the aquarium conditions can have a big effect on how well a pregnancy progresses, and whether or not the fetal fry develop normally and are brought to full term, or are aborted, delivered prematurely, or resorbed as embryos. In short, Sean, it’s important to handle your gravid male with care during his pregnancy, to keep him and his mate together, and to provide him with a nutritious diet, optimal water quality, and a stress-free environment at all times.

Best of luck with your new seahorses, sir! Here’s hoping that your Mustang presents you with a healthy brood about two weeks from now.

Respectfully,
Pete Giwojna