Re:orange eggs on aquarium bottom

Pete Giwojna

Dear beachbum:

Yup, judging from your description, those certainly sounds like seahorse eggs that were spilled during a 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. The eggs are negatively buoyant and sink to the bottom when released.

However, it’s extremely unlikely that they are unfertilized eggs that a gravid male purged or dumped out of his brood pouch. Any unfertilized eggs are normally gradually resorbed rather then expelled. When seahorses mate, a powerful sprinter muscle seals the aperture of the brood pouch tight the moment the female has transferred her clutch of eggs into the marsupium of the male. As a rule, a gravid male will not open his pouch again for any reason until he is ready to give birth. The intrusion of saltwater into the pouch can be harmful to the embryonic young in the early stages of pregnancy because it dilutes or displaces the marsupial fluid that is bathing the fetal fry, and opening the pouch in the later stages of pregnancy is equally disastrous since it may result in the expulsion of pug-nosed preemies still attached to yolk sacs. Ordinarily, once a male seals the aperture of his pouch after the transfer of the eggs, he will not open it again until the hormone isotocin triggers parturition and the birth spasms.

So I’m thinking it’s much more likely that the spilled eggs you observed are from a clutch of ova that were dropped during a botched or abortive mating attempt. That’s not uncommon with inexperienced pairs that often find coitus awkward and difficult to accomplish successfully.

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 some dropped eggs. Practice makes perfect, and sooner or later your pair will get it right and begin producing broods with clocklike regulary.

The spilled eggs are a sure sign that one or more of your stallions is trying hard to get pregnant, so if your male is not actually pregnant at the moment, chances are good that he will be before too long. However, a female that has dropped her clutch of eggs normally won’t hydrate more eggs and attempt to mate again until the next breeding cycle, so your pair may have to wait a few more weeks before they try again.

Best of luck with your seahorses, beachbum! Your seahorses are certainly displaying a healthy interest in courtship and mating, so the chances are excellent that they will present you with more offspring before long.

Happy Trails!
Pete Giwojna

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