Re:scattered eggs???

Pete Giwojna

Dear Seagazer:

Yup, it sounds very much like your seahorses spilled some of the eggs during their mating attempt. Hippocampus erectus ova are bright orange ovoids about 1.5 mm in diameter. Unlike most fish eggs, which are round or nearly so, seahorse eggs are pear-shaped. They are full of oil droplets and rich in carotenoids (yellow to red pigments), which help to provide an intracellular source of oxygen for the fetal fry. The presence of these pigments gives the eggs their characteristic orange coloration.

Female seahorses lack a true ovipositor or intromittent organ with which to deposit their eggs (Lawrence, 2003). Rather than a long egg tube, a nipple-like genital papilla (everted oviduct) is extended slightly (3-5mm) when the female is ready to mate, and she extrudes her eggs in a long sticky string through this simple structure (Lawrence, 2003). The entire clutch — up to 1600 eggs in some species — is transferred in one brief midwater embrace lasting a mere 5-10 seconds (Vincent, 1990). A ripe female loses up to 30% of her body weight after depositing her eggs (Vincent, 1990). The swelling of the female’s abdomen and slight protrusion of the oviduct are unmistakable indications that mating is imminent.

As Leslie mentioned, it is not uncommon for an inexperienced pair to spill some eggs during the copulatory rise while they are trying to execute the tricky, maneuvers required to successfully transfer the eggs. And if your female is considerably larger than the male, it’s certainly possible that she may have ripen more eggs than his pouch could accommodate, in which case she would have no recourse but to dump the excess eggs.

In order to ensure fertilization, the female must add water to her mature oocytes (egg cells) just prior to mating (Vincent, 1990). A ripe female is committed to mating once she has hydrated her clutch of eggs. She cannot retain the hydrated eggs indefinitely (Vincent, 1990). They can only be retained for approximately 24 hours, before they must be released. She must transfer these eggs to a receptive male within 24 hours of hydration, or lose the entire clutch. Should she be unable to transfer them to a receptive male within that time, she risks becoming egg bound, and her only recourse is to release them into the water column, spilling her eggs onto the substrate.

So under certain circumstances, it’s not at all unusual for eggs to be spilled while mating or even for a female to drop her entire clutch of eggs, if necessary. As long as your tank is tall enough to allow your seahorses to mate comfortably, you shouldn’t be at all concerned at discovering a few spilled eggs or for that several stray eggs remained dangling from your female’s vent afterwards. Practice makes perfect, and sooner or later your pair will get it right and begin producing broods with clocklike regulary.

Hippocampus erectus has an enormous range of the wild, crossing many lines of latitude, with a normal gestation period of anywhere from 14-30 days, depending primarily on water temperature. In the aquarium, gestation for erectus is usually 2-3 weeks. Under the current conditions in your seahorse setup, Seagazer, it sounds like the typical gestation period for your Hippocampus erectus is going to be around 15 days.

Are you concerned about the slightly abbreviated gestation period because your male has been unable to carry a brood of fry full term at your current water temperatures? Gestation in seahorses can be influenced by a number of factors, some of which can disrupt the pregnancy and prevent the embryonic young and fetal fry from developing normally. For instance, gestation is largely determined by water temperature, is controlled by the levels of key hormones, and can be influenced to a lesser degree by diet and nutrition.

As previously mentioned, Hippocampus erectus has a very wide range which encompasses different climate belts and it can adapt to a wide rage of temperatures. Different public aquarium keep erectus successfully at temps ranging from 55 F-82 F (13 C-28 C). In general, the warmer the water the shorter the gestation period, and vice versa. Here in the US, most hobbyists keep Sunburst at around 75 F, and a 2-3 week gestation period is about average for those conditions.

However, gestation may vary due to hormonal influences as well. For example, in seahorses, a hormone known as fish isotocin, which is the equivalent of oxytocin in mammals, triggers parturition or giving birth. 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 embryonic young, and the pregnancy itself are all controlled by various hormones — testosterone, adrenal corticoids, prolactin, and isotocin — so basically anything that influences the secretion of those key hormones can have a profound effect on the pregnancy. Because of such disruptions, hobbyists should beware that not all pregnancies will come to fruition.

Some of the factors that influence these hormonal responses are the presence of the female, low oxygen levels, 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. 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. 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. The male is thought to further expand his pouch and develop the placenta-like internal structures to a greater degree as a result. More of the eggs can then be successfully implanted and carried to full term. 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.

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. 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.

So the gestation period for a given species can vary according to a number of factors, Seagazer, and you’ll want to avoid those conditions we’ve been discussing which can be detrimental to the pregnancy.

Best of luck with your courting seahorses, Seagazer! Here’s hoping they get it right and provide you with a healthy brood of fry very soon.

Happy Trails!
Pete Giwojna

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