If I understand you correctly, you witnessed your pair of seahorses attempting to mate unsuccessfully on two occasions during which they were unable to successfully complete the egg transfer, with the result that the females spilled her clutch of eggs on the bottom of the tank. After that, you subsequently witnessed two other mating attempts which were unsuccessful and did not result in a pregnancy, but during which no eggs were spilled. You haven’t seen any new mating attempts recently and you’re wondering if the female may have stopped producing eggs, since none were spilled during the last couple of attempts to breed.
It is true that repeated failures to successfully transfer the eggs will sometimes discourage a pair of seahorses from attempting to breed, but that usually only happens when it is the physical conditions within the seahorse tank that prevent them from mating. The most common reason that this can happen is when the aquarium is simply too shallow to allow the couple to complete the egg transfer during the copulatory rise; when the seahorses cannot swim up high enough to carry out the tricky egg transfer in midwater, they may simply give up trying after a while.
But that doesn’t seem to be a problem in your case. You have a 65-gallon aquarium that is 30-inches tall, which is more than adequate for the seahorses to mate comfortably. And your seahorses have been able to rise up and attempt the egg transfer repeatedly, although thus far they have botched all of their mating attempts. Unless there is something else about your seahorse tank other than a lack of height that is preventing the seahorses from executing the difficult maneuvers required for the egg transfer, such as strong water currents in the upper 1/3 of the aquarium that the seahorses are having trouble overcoming when they rise up to mate, I suspect that your problems are primarily due to an inexperienced pair that have yet to master the copulatory rise and exchange of eggs. When that’s the case and there are no physical barriers that prevent the seahorses from copulating in midwater, I would expect your pair to continue trying until they finally get it right.
Under the circumstances, I think it’s unlikely that your female has stopped producing eggs, holdyourhorses. Females normally only ripen one clutch of eggs each breeding cycle, and for Mustangs and Sunbursts (Hippocampus erectus), a mating cycle is typically about one month or a little less. So if you are pair has attempted to mate recently, they may not try again for several weeks, at which time the females should have another clutch of fully mature eggs ready to go.
Seahorses are fractional spawners and very well adapted for producing clutch after clutch of eggs. Females maintain a spiraling assembly line of developing oocytes (egg cells) at all times, only a portion of which are fully mature and are released at each mating (Vincent, 1990). This differs from the reproductive strategy of most fishes, which are multiple spawners that release all their eggs each time they mate and then start over, maturing an entirely new clutch of eggs from scratch for the next spawning.
The structure of the ovaries is unique to syngnathids. They are paired organs, which join to form a single oviduct (the seahorse’s version of a Fallopian tube) just before the urogential pore (Vincent, 1990). Oocytes spiral out from the center of each ovary, creating a coiled sheet of developing eggs at differing stages of growth (Vincent, 1990). The earliest or primordial eggs arise from the germinal ridge that runs the entire length of the ovary, and lie at the center of the coil from which they spiral out as they develop so that the fully mature eggs are the furthest from the center of rotation (Vincent, 1990). Roughly 20-25% of the outermost eggs in this ovarian assembly line are mature, ready to be discharged during ovulation and deposited with the male (Vincent, 1990). Thus, fully 70-75% of the female’s developing eggs are retained in the ovaries after mating, so a new clutch of eggs will mature relatively quickly and lie in readiness for the next mating cycle.
Seahorse ovaries are always active, busy creating and developing new eggs (oogenesis), forming the yolk (vitellogenesis), and resorbing any mature ova (atresia) leftover after mating or at the end of the breeding season (Vincent, 1990). Eggs in all 4 stages of development can be found in the ovaries throughout the year.
So if your pair of seahorses has not attempted to mate recently, the female’s ovarian assembly line has mature eggs ready and waiting right now and she could hydrate them and mate successfully at any point — today, tomorrow, even right at this moment. But if they did attempt to mate recently, albeit unsuccessfully, it may not be for another month before the female is again receptive, with a full complement of mature eggs ready to be deposited with the male.
Most likely it is just a matter of time before your young pair of seahorses succeeds. Continue to provide them with optimum water quality, a highly nutritious diet, and a stress-free environment, and they soon eventually get it right. Good nutrition is especially important in order to ensure good egg production, since a large proportion of the female’s bodily resources go into producing a clutch of eggs. As an example, a female seahorse may lose over 30% of her weight following a successful egg transfer (or a dropped clutches of eggs). So make sure you keep your male and female well fed and maintain good water quality, and your efforts should be rewarded sooner or later.
Best of luck with your pair of ponies, holdyourhorses! Here’s hoping they produce many broods of healthy young for you in the months and years to come.