Re:Pregnant or not

#2480
Pete Giwojna
Guest

Dear Nigel:

Did you specify a pregnant male when you placed your order, or did you just order a mated pair?

If you ordered a gravid male, then you can rest assured that your stallion will deliver a brood of young in due course unless something untoward happens to disrupt his pregnancy.

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 your dissolved oxygen levels, Nigel!)

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.

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.

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, if you think you have a gravid male, Nigel, it’s important to handle him with care and to provide him with a nutritious diet, optimal water quality, and a stress-free environment at all times.

Best of luck with your seahorses, Nigel! Here’s hoping your Zulus will provide you with many broods of young in the months ahead.

Respectfully,
Pete Giwojna


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