Re:raising redi

#2514
Pete Giwojna
Guest

Dear Nigel:

Don’t count your chickens before they hatch, errr — your reidi babies before they are born, sir. The changes in your stallion’s pouch may simply indicate that he’s getting ready to breed, not that he’s already pregnant. Allow me to explain.

In some seahorse species, adult males and females can be very difficult to tell apart when they are not breeding because the male’s pouch shrinks to almost nothing in the offseason and does not become obvious again until hormonal changes triggered by courtship and mating cause it to grow and expand (Bull and Mitchell, 2002).

For example, this is how Michael Payne (Seahorse Sanctuary) describes this phenomenon:

"Temperature may effect whether or not you can see the pouch of a male. In H. breviceps, it is very difficult to sex adults that are not in breeding condition. At low temperatures (17°C), the males’ pouch deflates such that you can hardly see it. Increase the temp (22°C) and the brood pouch appears and mating starts."

During the breeding season, the male’s brood pouch undergoes elaborate changes to prepare it for pregnancy. 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 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).

In the offseason, the levels of gonadotropin, testosterone and adrenal corticoids in the bloodstream are reduced, and the pouch deflates and shrinks accordingly, reversing these placenta-like changes. So the changes you have noticed in your male’s pouch are good signs, but the enlargement of his pouch could merely indicate that your reidi are getting serious about courtship and breeding now, so their hormones are flowing and he is preparing his pouch for eggs. It doesn’t necessarily mean that your male has already mated successfully, just that he is ready to breed..

Also, don’t assume that your Brazilian seahorse (H. reidi) will produce a small brood. It is indeed true that virgin males often produce inordinately small broods of fry the first time they mate, but "small" is a relative term. The Brazilian breeding machine is the most prolific of all the seahorses (Abbott 2003). They have a well-deserved reputation for churning out brood after brood every two weeks with relentless regularity, and hold the world record for delivering ~1600 young in a single brood (anecdotal reports of broods up to 2000 fry are not uncommon)! Not bad for a livebearer.

Large well-fed males routinely produce broods in the 1000-1200 fry range, and an average brood for H. reidi consist of several hundred young. So even a young, inexperienced male’s first brood could easily run into three figures. If he is already pregnant, or becomes so in the near future, don’t be surprised if you are looking at well over 100 fry when your reidi stallion delivers.

Best of luck with your prolific ponies and all of their future progeny, Nigel!

Happy Trails!
Pete Giwojna


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