Re:STILL PREGNANT?

#3492
Pete Giwojna
Guest

Dear saltfreak:

It’s certainly possible that your male is still pregnant, sir. The gestation period for Hippocampus erectus varies considerably with water temperature, diet, latitude, and even the lunar cycle, but is usually around 20-21 days (+/- 10 days). The recorded gestation for H. erectus ranges from a mere 11 days to over 30 days. My best guesstimate is that your gravid male was probably about a week pregnant when he was shipped to you, so a normal brood may still be forthcoming any day now.

I don’t think the blob you noticed previously represents a miscarriage. Any number of things can delay or disrupt a pregnancy, but when a pregnancy is actually aborted, the male may undergo labor and expel dozens of stillborn young. More often, however, if something happens to interrupt or disrupt a pregnancy, the male simply resorbs the eggs or fetal fry he is carrying and nothing is expelled, as discussed below:

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.

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.

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, and a stress-free environment at all times. Those are the most important things you can do to help assure that all goes well and the pregnancy isn’t interrupted, sir.

Best of luck with your new seahorses, saltfreak! As long as your male seems very healthy, I don’t think there’s anything to be concerned about. If, for any reason, he doesn’t carry his pregnancy full term this time, the chances are good that he will soon be pregnant again and produce a healthy brood of fry next time.

Respectfully,
Pete Giwojna


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