False pregnacy?????????

Dear Cherie:

Regarding your pregnant male, most likely either your camel shrimp decimated the newborns or something happened to disrupt the pregnancy and cause the embryonic young or fetal fry to be aborted or resorted. I would be happy to discuss both of those possibilities in more detail below so we can help you avoid such problems in the future.

Decorative shrimp and cleaner shrimp — indeed, shrimp of all kinds — will predate newborn seahorses. This includes Peppermint Shrimp (Lysmata wurdemanni), Scarlet Cleaner Shrimp or Skunk Cleaner Shrimp (Lysmata amboinensis), Fire Shrimp (Lysmata debelius) and the pugnacious Boxer Shrimp or Banded Coral Shrimp (Stenopus hispidus). Shrimp such as these that are active swimmers are the worst offenders when it comes to dining on seahorse fry. Bottom-dwelling shrimp like your camel shrimp are less likely to be troublesome in that regard, although they can certainly take a toll on the fry when they settle to the substrate.

Peppermint shrimp (Lysmata wurdemanni) are a favorite with seahorse keepers because they eat Aiptasia rock anemones, and both the peppermints and Scarlet cleaner shrimp (Lysmata amboinensis) will perform another useful service by grooming the seahorses and cleaning them of ectoparasites. As an added bonus, they reproduce regularly in the aquarium, producing swarms of larval nauplii that the seahorses love to eat. But shrimp in general must be excluded from nurseries and grow-out tanks because they regard newborn seahorses as tasty treats.

It’s also 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, Cherie. 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, although ultimately nothing came to fruition, Cherie.

If it’s any consolation, Cherie, now that your seahorses have begun breeding, they should produce a new brood of young for you every month or so during the breeding season.

Best of luck with your seahorses and their next brood of newborns, Cherie!

Respectfully,
Pete Giwojna