Well, sir, I don’t know quite what to make of your situation and I have given the matter quite a bit of thought. In your initial post, you stated that you have tried most everything you can possibly think of an order to encourage your seahorses to breed, all to no avail, and you asked why it is that your ponies won’t breed. In the additional information you provided, you mentioned that year two pairs of Hippocampus erectus seahorses court quite frequently, and that the males are always trying to persuade the females to give it a go. And you say that occasionally the females are responsive to the males’ overtures, but that nothing ever seems to come of it. Finally, you mentioned that, on one occasion, you found eggs all over the bottom of the tank. The spilled eggs you found are clear evidence of a serious mating attempt that failed at the last instant, during the actual transfer of the eggs.
As you know, John, 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 slightly 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. The eggs are also very sticky or adhesive.
Seahorse roe is indeed very nutritious due to the rich yolk supply, and the scavengers in the tank typically make short work of them, scarfing them up like caviar — quite literally.
In short, John, 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 fact, it’s quite possible that there have been other botched mating attempts that you are unaware of because the evidence was cleaned up before you had a chance to witness the dropped eggs.
In order to ensure fertilization, the female must add water to her mature oocytes (egg cells) just prior to mating. A ripe female is committed to mating once she has hydrated her clutch of eggs. She cannot retain the hydrated eggs indefinitely. 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.
The actual transfer of eggs takes place at the apex of the copulatory rise while the couple is suspended in midwater or slowly descending toward the bottom — a maneuver that is every bit as tricky as it sounds. Coitus is marked by an extremely awkward, fleeting embrace, aptly described as little more than a brief belly-to-belly bumping.
As you can imagine, many difficult and delicate maneuvers are required to bring the pair into proper position for this most improbable merging, and inexperienced pairs often struggle to get it right. The female will attempt to insert her oviduct into the gaping aperture of the male’s inflated brood pouch. An inexperienced pair will often end up misaligned, perhaps at right angles to one another or with one of the partners too high or too low to join. This is very typical of the many false starts and abortive attempts that are ordinarily involved. The frustrated couple may even separate to rest on the bottom briefly between mating attempts. They may require many such rises before the proper positioning is achieved and the crucial connection is finally made.
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 regularity.
At any rate, the spilled eggs are a sure sign that one or more of your stallions is still trying hard to get pregnant and that at least one of the females is receptive and doing her best to oblige him. 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.
Sometimes during a botched mating attempt some of the eggs will find their way into the male’s pouch, and these eggs will be fertile and may result in a pregnancy, albeit with a much smaller brood than normal, even if the majority of the eggs were spilled during mating. In the aquarium, it’s not uncommon at all for an experienced pair to spill some of the eggs when mating, and when that happens, any of their eggs that do make their way into the male’s pouch will be fertilized and develop normally. If the bulk of the eggs were spilled, the male will subsequently deliver an unusually small brood, and his brood pouch may not expand noticeably because of the small number of fetal fry and embryonic young he is carrying. Under those circumstances, the size of the pouch is not a reliable indicator of pregnancy and it can be difficult to determine whether I’m not the male is really gravid until he actually gives birth.
All things considered, John, it sounds to me like the conditions in your aquarium are conducive to mating. You are witnessing plenty of courtship activities, you have seen receptive females respond to the advances of the stallions, and there has been at least one attempted egg exchange, which is the climax of a serious attempt to breed. It sounds like your seahorses have a healthy interest in breeding and that the environmental conditions in your aquarium are not the problem.
If anything, sir, I would focus your efforts on determining why is that the seahorses are unable to successfully complete the egg transfer. This could be due to a lack of vertical swimming space, since mating occurs at the apex of the copulatory rise, and if there is not enough swimming room to allow for the necessary maneuvering near the surface of the aquarium, the lack of height may be making it very difficult for your ponies to achieve coitus. (You never mentioned how tall your 30-gallon aquarium is, John, so I cannot rule out the possibility that there is not enough vertical swimming space for successful mating.)
Or, there may be too much water movement near the surface of the tank. If there are swirling currents, or tricky crosscurrents near the top of the aquarium, the seahorses will find it very difficult to make the crucial connection when they rise to meet.
Look for something along those lines, John, and if all seems well in your seahorse setup in that regard, then most likely you simply need a little more patience. In the wild, both temperate and tropical seahorses breed best during the summer months and typically take a break from breeding during the offseason. Breeding may therefore naturally tape are off and grind to a halt in late fall and winter, and with wild seahorses in particular, many times there is nothing nothing’s wrong but the calendar when a mated pair fails to reproduce. Even captive-bred seahorses sometimes experience a lull in the festivities at this time of year. That’s just their natural breeding cycle, the rhythm of life built into their genes. There is a good chance that with the return of springtime, your seahorses’ fancy will once again turn to thoughts of love.
In other words, John, now that April has arrived, you can expect the courtship activities of your seahorses to gain steam and I wouldn’t be surprised if you have some successful matings and broods of young being produced by late spring/early summer. As you noted, the stallions are always in the mood, and the females are more likely to be receptive and respond favorably as summer approaches.
Best wishes with all fishes, John! Here’s hoping that your H. erectus prove to be prolific ponies that produce plenty of offspring for you in the months and years ahead.