Re:Mother’s Day

#4191
Pete Giwojna
Guest

Dear Lisa:

WooHoo — 7 more six-week old juveniles Sunbursts than you thought you had! That’s a nice surprise once you had in opportunity to perform an actual snout count of the youngsters. The survivors from the first brood must be almost 7 weeks old now — raising 57 of the Sunburst babies to that age is quite a remarkable achievement, especially for your first attempt at rearing! Keep up the great work!

No doubt about it — rearing seahorse fry for the home hobbyist is a time consuming task that requires a Herculean effort, but it’s also tremendously rewarding. Nothing gets you more bragging rights or respect and admiration at your local Aquarium Society or local fish store that having a tank full of healthy homegrown seahorses to show off.

I think getting mated pairs is definitely the way to go, in most cases. The seahorses certainly enjoy a richer, more natural life when they have the opportunity to interact, court one another, pair up and reproduce. And the hobbyist has a chance to observe social interactions and behaviors he would otherwise never see, such as competition for mates and daily greetings and birthing, including one of the grandest spectacles in all of nature — the colorful courtship and mating ritual of the seahorse!

Over a period of days, the partners perform a series of ritualized maneuvers and distinct displays — brightening, reciprocal quivering, pumping, pointing, and several delightful dancelike displays (the carousel dance, Maypole dance, and the parallel promenade) — all culminating in the copulatory rise and exchange of eggs. Once a pair has bonded, these maneuvers are repeated regularly in a daily greeting ritual that strengthens and reinforces the pair bond. In my opinion, the seahorses have a better quality of life when they are allowed to engage in these activities in the aquarium, even if it ultimately means sacrificing their young.

In short, keeping mated pairs provides behavioral enrichment for the seahorses and they are happier and healthier as a result.

As you know, Lisa, male seahorses undergo a true pregnancy and most hobbyists find the birthing process to be every bit as fascinating as their amazing courtship and greeting rituals. Male seahorses nourish the developing young in a special brood pouch. Often called the marsupium, this remarkable organ is much more than a simple sack or protective pocket or a mere incubator for the eggs. Think of it as an external womb, which undergoes placenta-like changes throughout the pregnancy in order to meet the needs of the fetal fry. Its internal architecture is surprisingly complex. In fact, the male must begin preparing his pouch to receive his next brood long before gestation begins (Vincent, 1990). The elaboration of the internal pouch anatomy that is necessary to support the developing young is triggered by the male hormone testosterone. The development of these structures is thus under testicular control and takes place primarily in the offseason when the seahorse is not breeding (Vincent, 1990). The four layers of tissue that comprise the pouch undergo increased vascularization at this time (Vincent, 1990) and a longitudinal wall of tissue or septum grows up the middle of the pouch, separating it into left and right halves. This increases the surface area in which fertilized eggs can implant, and enriches the blood supply to the lining of the pouch in which they will imbed. Just before mating occurs, this is enhanced by a surge in the active proliferation of the epithelial tissue that forms the innermost layer of the pouch (Vincent, 1990).

These placenta-like changes accelerate after the actual mating and transfer of the eggs take place. The male releases his sperm as the eggs are deposited. The moment the last egg is nestled safely inside the pouch, a ringlike sphincter muscle seals it off (Vincent, 1990). The fertile eggs implant in the wall or septum of the pouch, triggering a spongelike expansion of its tissues as the capillaries and blood vessels swell and multiply. Epithelial and connective tissue proliferate around the embedded eggs, enveloping each ovum within a tiny chamber or alveolus of its own (Vincent, 1990). Eventually 7/8 of every embryonic sac is embedded in the spongy tissue lining the pouch (Vincent, 1990). Each compartment or alveolus opens into the central cavity of the pouch. About 1/8 of each embryo remains exposed, protruding through this opening, and is immersed in a special placental fluid within the pouch (Vincent, 1990).

In this way, the brood pouch is prepared to maintain the pregnancy by carrying out the following vital functions:

(1) Protection. The brood pouch protects the young in a number of ways. It shields them from harmful ultraviolet radiation, which can destroy unprotected eggs and larvae (Vincent, 1990). It shelters the eggs and fetal fry from predators, and protects them from siltation and suffocating algae (Vincent, 1990).

(2) Aeration. A dense network of capillaries forms in the connective tissue that surrounds each of the embedded eggs, delivering oxygen to the fetal fry through the membrane of the embryonic sac (Vincent, 1990) and carrying away their metabolic wastes in the same manner.

(3) Control of osmotic pressure. The sealed pouch creates a watertight environment for the developing young and, over the course of the gestation, the male adjusts the osmotic pressure from that of his bodily fluids to that of seawater (Vincent, 1990). The young are thus gradually acclimated to full-strength saltwater over the course of the pregnancy, so the newborns will be right at home when they are expelled from the pouch. This is crucial for the survival of the delicate fry, since sudden changes in osmotic pressure are known to cause stunting, breathing abnormalities, and physical deformities in teleost fish larvae (Vincent, 1990).

(4) Nourishment. A portion of each embryonic sac is bathed within a nourishing placental fluid containing calcium and other inorganic ions contributed by the male (Vincent, 1990). The placental fluid also contains organic ions derived from the female via the yolk. The male secretes enzymes that dissolve away the outer covering of the eggs (chorion) shortly after incubation begins, and the organic ions contributed by the female diffuse across the exposed membrane of the embryonic sac into the pouch fluid (Vincent, 1990). There they are transformed into amino acids by a special enzyme (protease) secreted by the pouch epithelium (Vincent, 1990). These amino acids eventually become proteins incorporated within the embryos (Vincent, 1990). The calcium provided by the male is similarly taken up by the embryos and infused into their skeletons (Vincent, 1990).

In short, the brood pouch enfolds, protects, aerates, osmoregulates, and nourishes the developing embryos as the male undergoes a genuine pregnancy (Vincent, 1990). The gestation period in the genus Hippocampus lasts anywhere from 10 days to 6 weeks depending on the species and the water temperature (Vincent, 1990). The volume of the pouch increases dramatically as the pregnancy progresses. A male that is carrying a significant number of young becomes very rotund so that only a very thin layer of epithelium and connective tissue separates the interior of the pouch from the outside world by the time birth is imminent (Vincent, 1990).

The fully developed young emerge from their individual compartments and shake loose into the lumen of the pouch prior to birth (Vincent, 1990). They become very active toward the end of the pregnancy and can sometimes be seen wriggling about through the membrane of the swollen brood pouch. This appears to be every bit as uncomfortable as it sounds, since expecting males become agitated and distressed as the big moment approaches. They experience definite labor pains when birth is imminent, evident as a series of powerful contractions, and soon begin pumping in time with these birth spasms in order to forcibly eject the fry from their pouches. Labor usually begins well after dark in the early morning hours (Vincent, 1990). The distraught male may pump and thrust vigorously for hours before finally ejecting the first of the newborns (Vincent, 1990). The fry are expelled singly or in ones and twos at first, but are soon spewing forth in bunches and bursts of a half dozen or more.

Delivering a large brood this way is hard work, and the exhausted male will pause periodically to recover from his exertions, gathering his strength until he is caught in the throes of another round of contractions. In some cases, it takes 2-3 days for the entire brood to be delivered in this manner.

No matter how often I see a male giving birth, it never ceases to amaze me. Watching the fry erupt into existence that way is an incredible sight. They are perfect miniature replicas of their parents, able to fend for themselves from the first. It seems a brutal beginning, a ruthlessly rude awakening, to be violently thrust into the world in such an abrupt fashion, but the newborns hit the water swimming without missing a stroke. It’s a thrill to be witnessing such a miracle of nature and always leaves me awed and exhilarated! That’s another good reason for allowing your seahorses to do what comes naturally — pair up and mate.

So please don’t regret your decision to order a mated pair of Sunbursts rather than two females or two males, Lisa. It’s good for the seahorses and fascinating for the fish keeper, and all of your hard work has certainly been well rewarded, in your case.

Best of luck finding foster parents and adopting out the surplus fry from your Mother’s Day brood when the time is right, Lisa!

Happy Trails!
Pete Giwojna


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