Re:What Happened

#4308
Pete Giwojna
Guest

Dear Grant:

It’s difficult to say what’s going on with your stallion, sir. It’s possible that something may have disrupted the pregnancy and caused the male to resorb the eggs and/or embryonic young, or it’s possible that he may have given birth in the early morning hours and that the filters or his tankmates may have eaten the newborns.

For example, it’s not 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. If it’s been nearly 2 weeks since your male became pregnant, he may have delivered a portion of his brood shortly before or after sunrise, which is when the vast majority of males give birth, and this first batch of newborns may have been filtered out by your filtration system or predated by his tankmates, leaving none of the young for you to find. You might want to check your prefilter and filter box for any sign of the seahorse fry, just in case.

Otherwise, I suspect that something may have disrupted the normal course of the pregnancy and prevented your male from completing gestation. When that happens and gestation is interrupted, hobbyists often describe the phenomenon as a phantom pregnancy or a false pregnancy or a miscarriage.

Several things can interrupt a pregnancy and cause a gravid male to lose the embryonic young or fetal fry he is carrying. For example, 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, 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. (So check the dissolved oxygen levels in your Biocube, Grant!)

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 affects 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."

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, it’s important to handle gravid males with care and to provide them with a nutritious diet, optimal water quality, good levels of dissolved oxygen, and a stress-free environment at all times. Those are the most important things you can do to prevent the recurrence of this problem in the future, Grant.

Best of luck with your seahorses, sir! Here’s hoping that your pair provides you with a healthy brood very soon.

Respectfully,
Pete Giwojna


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