Re:Mating Problems

#4420
Pete Giwojna
Guest

Dear Sean:

Yes, sir, I do recall the incident in which you’re pregnant male aborted his pregnancy prematurely. I am surprised to hear that there have not been subsequent mating attempts since that time.

The best way to help the process along is to obtain a mated pair of seahorses, give them a nutritious diet of Vibrance-enriched frozen Mysis, maintain optimum water quality at all times, and provide them with a stress-free environment in which to live, as discussed in greater detail below. Assuming that your seahorse tank is tall enough to allow your pair to mate comfortably, which I assume much be the case since they have already mated successfully once and accomplished the transfer of eggs, it sounds like you’re doing just about everything right.

For whatever it’s worth, here are some more suggestions for encouraging breeding, Sean. You seem to be well aware of most of the factors that can have an adverse affect on breeding in the aquarium, so I realize that little of the following information will apply in your case, but let’s review it all again once more just for the sake of thoroughness:

Breeding Problems

Basically, to encourage courtship in breeding in domesticated seahorses, you simply need to provide them with optimum water quality, a highly nutritious diet with proper enrichment, and a stress-free environment, and then let nature take its course. Make sure they have enough hitching posts and shelter to provide them with a sense of privacy, yet adequate space and swimming room to perform their courtship displays, conduct their mating dance, and carry out the copulatory rise and transfer of the eggs.

A great many factors influence courtship and breeding in the aquarium, ranging from hours of daylight or photoperiod to water depth to diet and nutrition. Breeding may be inhibited in shallow tanks or by ambient noise and vibrations, disruptive tankmates, stress, poor water quality, or even inappropriate aquarium decor.

Photoperiod.

Surprisingly, it isn’t falling water temperatures alone that determine the breeding season for many seahorses in the wild but rather decreasing temps combined with the decreasing hours of daylight that control their reproductive activity. Dwarf seahorses (Hippocampus zosterae) are a perfect example of this, breeding best when the days are longer than 12 hours (Strawn 1953; Strawn 1954; Strawn 1958). They stop breeding altogether when the period between sunrise and sunset is less than 11 hours (Strawn 1953, 1954, and 1958). So you may have literally been turning off your seahorse’s breeding instincts with the flick of a switch if you are in the habit of switching off your aquarium reflector after 8-10 hours each day! Keep your aquarium lighted for 12 hours a day and your breeding problems may be a thing of the past.

To understand why the photoperiod is so important, we must first understand how the light-dark cycle regulates the levels of key hormones that control breeding. Gonadotropin (GtH) is a hormone that stimulates the growth and activity of the gonads and thus controls reproductive activity in vertebrates. It is secreted by the pituitary gland and stimulates the growth and function of the ovaries and testes. The levels of gonadotropin in the body are in turn regulated by melatonin, a hormone secreted by the light-sensitive pineal gland in response to darkness. Among a great many other functions, melatonin switches on a recently discovered enzyme known as gonadotropin inhibitory hormone, thus reducing the levels of gonadotropin in the body and shutting down reproduction (Sanders, 2005).

In other words, when the days are shortest and there is less sunlight, melatonin secretion is high and the levels of gonadotropin are reduced accordingly, causing the gonads to shrink and turning off reproduction. Likewise, when the days are longest and there is more sunlight, melatonin secretion is low and the levels of gonadotropin are high, stimulating the gonads and triggering reproductive activity (Sanders, 2005).

For best results, I recommend going beyond simply lighting your aquarium for 12+ hours every day. The best option is to provide your seahorses with a natural photoperiod that changes will the seasons (Indiviglio, 2002) and includes twilight periods at "sunrise" and "sunset." The simplest way to achieve this is to use power compact (PC) light fixtures. Choose a dual ballast fixture that includes two bulbs — one actinic tube and one daylight fluorescent tube – each controlled separately by its own ballast (Jennifer Myerscough, pers. com.). Each ballast can be placed on a separate automatic timer, making them perfect for this application. Adjust the timers so the bluish actinic tube comes on before the daylight tube and stays on after the daylights go off, thereby providing your seahorses with a simulated dusk and dawn (Jennifer Myerscough, pers. com.). You can also adjust the timers to lengthen or shorten the daylight periods in accordance with the changing seasons, which will help the seahorses maintain a natural reproductive cycle (Indiviglio, 2002). Since courtship is conducted primarily in the twilight hours just after dawn, a photoperiod of 2 hours half-light (actinic only)/12 hours full light (actinics + daylights)/2 hours half-light (actinic only)/8 hours darkness is highly recommended. If you cannot afford PC lighting, the half-light periods can be easily arranged by positioning a room lamp a short distance away from the tank instead, which comes on before and remains on after the aquarium reflector does.

Water Depth:

Some breeding projects are doomed to failure from the moment the aquarist picks out the aquarium for his seahorses (Giwojna, Jan. 1999). This can happen when a hobbyist selects a tank that is simply too shallow for the type of ‘horses he wants to raise (Giwojna, Jan. 1999). Seahorses are vertically oriented, and their upright swimming style is best suited to tall aquaria. More importantly, they rise vertically through the water column in order to mate, and if the aquarium is too shallow, they may be physically unable to copulate and transfer the female’s eggs into the male’s pouch for fertilization (Vincent. 1995b). This is an important consideration when breeding the largest species such as Hippocampus ingens, H. abdominalis, H. erectus and H. reidi. For instance, Australian breeders report that reducing the water level to below 500cm or about 20 inches deep can completely interrupt reproduction in Potbelly seahorses (H. abdominalis; Michael Dickson, pers. com.).

As a general rule of thumb, seahorses must have a minimum of 2-3 full body lengths of open water (top-to-bottom swimming space) above the substrate in order to mate comfortably (Giwojna, Jan. 1999). This will allow them to swim upwards for at least one full body length when they rise from the bottom and attempt to transfer the eggs. In other words, if you want to breed that prize 10-inch Potbelly seahorse of yours, you will need to provide him and his mate with a tank that is at least 20-inches tall; 24-30 inches of height would be safer (Giwojna, Jan. 1999).

When selecting a breeding tank, bear in mind that the ”two-to-three-body-lengths” rule applies to the depth of the water in the aquarium, not the height of the tank per se (Giwojna, Jan. 1999). If you keep the water level in the tank an inch from the top and have an inch of calcareous gravel or crushed coral on the bottom, a 12-inch tall aquarium only has 10 inches of vertical swimming space. With such a tank, the hobbyist would thus be restricted to one of the small or medium-sized species that attain an adult height of no more than 3 to 5 inches from the tip of their coronet to the tip of their tail. For example, a pair of 7-8 inch Hippocampus erectus may have difficulty mating in a tank that is only 16-inches high, since they need around 15 inches of vertical swimming space for the copulatory rise, and you must account for the air space at the top of the tank as well as the depth of the substrate (Giwojna, Jan. 1999). I always recommend keeping seahorses in aquariums that are least 20 inches tall, and tanks that are 24 inches tall and above are even better.

The urge to breed is very strong in Hippocampus, however, and if kept in a shallow tank, pairs will do their best to improvise, adapt, and overcome such depth limitations. I have seen pairs whose copulatory "rise" was more horizontal than vertical, yet which managed to mate successfully. Typically, the shallower the tank, the more difficult coitus is to achieve and the more likely it becomes that eggs will be spilled during the transfer. Eventually this reaches the point where entire clutches are being lost, which is when most pairs cease trying and no longer attempt to breed (Giwojna, Jan. 1999). But breeding can be inhibited in large seahorses that are kept in aquaria less than 20 inches tall.

Worse still, shallow tanks increase the danger that an overripe female may become egg bound. In a tank with inadequate water depth, a courting female that has hydrated her clutch may be unable to make the egg transfer, yet she will be reluctant to dump the eggs while a receptive male is still standing by eager to receive them. If she is overly optimistic and retains her clutch too long, hoping to pull off the tricky egg transfer despite the lack of depth, she may become egg bound. Her lower abdomen will become very swollen and prolapsed tissue may protrude through the vent as the pressure builds up. If she is unable to release the eggs at this point and relieve the pressure, death will result. An egg-bound female is thus a very serious complication of depth limitations (Leslie Leddo, pers. com.)
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Disruptive Tankmates:

Seahorses are shy, secretive creatures that rely on camouflage as their sole means of protection. During courtship and breeding, however, they suddenly become quite conspicuous, exchanging their drab, cryptic coloration for bright courtship colors. The couple is at their most brilliant at the climax of courtship when they rise to mate.

Needless to say, the brightly colored seahorses are extremely vulnerable and entirely defenseless as the female transfers her eggs to the male’s pouch while hanging suspended in midwater, and they will not put themselves in this vulnerable condition if they feel threatened in any way (Giwojna, Jan. 1999). Unruly tankmates are one such threat. As always, aggressive or territorial fishes must be assiduously avoided. In a small tank, even the normal day-to-day activities of harmless, nonaggressive tankmates may be enough to inhibit courtship and mating if they are active fishes that are always on the move, constantly swimming back and forth (Giwojna, Jan. 1999). Certain wrasses and tangs or surgeonfish fall in this category.

Aquascaping:

Hippocampus relies on camouflage and remaining hidden for its very survival. Seahorses can thus become distressed and agitated if their tank is too barren to provide adequate cover (Vincent, 1995b). This is particularly true during courtship and mating when the increased activity level and heightened coloration make them highly conspicuous and vulnerable, and breeding may be severely inhibited under these conditions (Giwojna, Jan. 1999). It’s important to keep the seahorses’ need for privacy in mind when aquascaping your seahorse tank. Be sure to provide enough shelter and sight barriers to allow them to completely conceal themselves from view should they want to be alone.

In order to accommodate them, I like to use an amphitheater-style arrangement when decorating my seahorse setups that provides plenty of cover at either end of the tank, while leaving the center of the aquarium relatively bare to act as a sort of ”dance floor” for the seahorses’ breeding ballet. On the other hand, a sparsely furnished, utilitarian design scheme, perhaps with nothing more than a few holdfasts and a bare bottom, is to be avoided (Giwojna, Jan. 1999). (Such sterile environments are commonplace when seahorses are being maintained under laboratory conditions.) A Spartan setup such as this facilitates feeding, water changes and maintenance, in general, but it can adversely affect the behavior of the inhabitants and prevent seahorses from breeding (Giwojna, Jan. 1999).

Ambient Noise — Shock and Mechanical Vibration:

Hippocampus has excellent hearing and the medium of water transmits sound wonderfully well — far better than air, in fact — so it’s not surprising that seahorses are acutely sensitive to ambient sound, external noises, and outside sources of shock and vibration. Certain frequencies can completely shut down breeding.

Excessive noise and vibration must be eliminated from the breeding tank no matter what the offending device may be — a clunky air pump or compressor, the buzzing ballast from an aquarium reflector, the rattling impeller from a noisy power filter or something totally unrelated to the aquarium, like a nearby clothes washer/dryer, dishwasher, stereo, television or some such appliance (Giwojna, Jan. 1999). The successful breeder must therefore choose the location for his seahorse tank with care. All potential sources of shock and vibration should be dampened. A cushioning pad placed beneath the tank will serve to deaden vibrations and soften any shocks that might otherwise be absorbed through the base of the aquarium (Giwojna, Jan. 1999). The aquarium pad should consist of a sheet of cork or Styrofoam at least 1/4-inch thick that extends slightly beyond the base of the aquarium on all sides (Giwojna, Jan. 1999).

Balky air compressors are best kept in another room while running a separate airline from there to the aquarium (Giwojna, Jan. 1999). Other damping measures include mounting noisy equipment such as air pumps on thick blocks of foam rubber. Try using a 4-6 inch block of foam with a shallow 1-2 inch deep cut out area that conforms to the contours of the device in question to hold it securely in place (Giwojna, Jan. 1999). Raise the aquarium reflector above the rim of the tank so that it is not in direct contact with the cover or the rim of the aquarium itself (Giwojna, Jan. 1999). The reflector can either be suspended over the tank or propped up on shims of cork, Styrofoam, or heavy cardboard. The idea, as far as possible, is to isolate the seahorse-breeding tank from outside noise and vibration (Giwojna, Jan. 1999).

Water Quality:

As with all fishes, even trace amounts of toxic ammonia and nitrite can be harmful to seahorses and prevent mating. Although nitrate is relatively harmless, high levels of nitrate will also affect breeding. In my experience, breeding is inhibited in many species once the concentration of nitrates rises above 20 ppm.

To assure ongoing reproductive success it is important to maintain optimum water quality and keep nitrate levels as low as possible. For best results, consider adding live rock, a live sand bed (preferably situated in your sump), and a good protein skimmer to your seahorse setup. Don’t overstock, don’t overfed, remove leftovers promptly, grow and harvest macroalgae, practice good aquarium management and maintain a sensible schedule for water changes. If necessary, add a denitrator to keep your nitrate levels low.

As a rule, the better your water quality, the healthier your seahorses will be and the better they will breed.

Stress:

As we all know, chronic stress can put a strain on even the strongest relationship, and that holds true for Hippocampus as well as Homo sapiens. There are a great many things besides water quality can be stressful for captive seahorses. These factors must also be addressed if you expect to have success breeding these amazing animals. Suffice it to say stressed seahorses will have little interest in breeding.

Diet:

Obtaining healthy, well-conditioned broodstock is a vital first step for anyone who hopes to breed these fascinating fish (Giwojna, Jan. 1999). This was a major problem for breeders back in the Dark Ages of seahorse keeping when wild specimens were the only option. By the time they finally arrive at your local dealers, wild seahorses have spent a long time in the collector’s holding tanks followed by an indefinite stay at a wholesaler and then a long trip to a local retailer. Due to their need for live foods, they are very likely to have gone unfed during this entire period, and they are often malnourished by the time they reach your neighborhood fish store (Giwojna, Jan. 1999). Fattening them up and keeping wild-caught seahorses in top condition is equally problematic, since they are finicky eaters that require hard-to-provide live foods in large amounts on a daily basis.

Fortunately, the advent of captive-bred seahorse has made obtaining well-conditioned broodstock a great deal easier. Tank-raised seahorses that have been born and bed for life in captivity through several generations make ideal broodstock. Such specimens reach the hobbyist in prime condition, at the very peak of health and stamina, and are already accustomed to eating aquarium fare and well adjusted to aquarium life.

Nevertheless, it is still important to assure that your breeders receive a nutritious diet rich in highly unsaturated fatty acids (HUFA) and other lipids. Producing clutch after clutch of eggs, and churning out brood after brood of fry, is very energetically demanding and places a serious strain on the bodily resources of breeding seahorses (Giwojna, Jan. 1999). Pairs that are receiving a marginal diet won’t be able to keep up and will thus lose interest in breeding sooner or later as a result (Giwojna, Jan. 1999). To avoid this, use a variety of good enrichment products to fortify their food and liberally supplement their staple diet of frozen Mysis with choice live foods, if possible. Remember a pregnant male is not just eating for two, as the cliche goes — rather, he must keep up with the metabolic demands of several hundred embryos.

It is equally important to make sure that gravid males receive adequate amounts of bioavailable calcium (Giwojna, Jan. 1999). Seahorses and pipefish that receive a diet deficient in calcium suffer from "soft plate" syndrome, which is characterized by decalcification of the bony plates that cover their bodies like a suit of armor (Greco, 2004). In the olden days, seahorses commonly developed this condition after being fed a diet consisting solely of Artemia, which contain inadequate levels of calcium and an imbalanced ratio of calcium to phosphorus (Greco, 2004).

For example, the New York Aquarium reports that pipefish and seahorses that are fed Artemia salina (brine shrimp) as a major portion of their diet, exhibit shortened lifespans, decalcification of their exoskeleton, and poor survival rate amongst their fry (Greco, 2004). Seahorse fry are known to incorporate calcium provided by their father into their skeletons (Vincent, 1990), so if Dad is deficient in calcium, his offspring will lack it as well. In that event, the rapidly growing fry will thus suffer high mortalities due to a condition akin to rickets in human children.

Breeding seahorses can be provided with adequate levels of calcium in either of two ways — by enriching their food supply or by enriching the aquarium water itself (minerals can be obtained by fish directly from the water). For instance, Heather MasonJones was successful breeding Hippocampus zosterae by enriching the brine shrimp she fed them with Kalkwasser (MasonJones and Lewis, 1996). Other aquarists prefer to add Kalkwasser (calcium hydroxide) directly to the breeding tank via an automatic doser in the same manner as many reef keepers enrich their systems (Giwojna, Jan. 1999). Many commercially made calcium supplements are available for reef aquaria that should work equally well.

Seasonality

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.

Incompatibility:

If all else fails, you may simply be dealing with an incompatibility problem. Even when seahorses are in the mood and actively courting, a certain percentage of courtships still fail to produce a pair bond for reasons largely beyond our understanding. Suffice it to say either partner may reject the other at any stage of their prolonged courtship ritual, although when initial pairings fail, it has been my experience that it’s almost always the female who rejects her suitor(s) (Giwojna, Jan. 1999).

The most common cause for rejection is a discrepancy in size. Seahorses tend to select mates of equal or greater size since both males and females can benefit from robust partners (Vincent and Sadler, 1995). Males prefer large females, which can provide bigger clutches and eggs with a greater supply of yolk, thereby producing more progeny (Vincent, 1990). Females likewise prefer robust males, since the bigger the brood pouch, the more eggs the male can carry and the more offspring the pair can produce (Vincent, 1990). When considering brood stock, it is advisable to select males and females that are closely matched in terms of body size and weight.

But when it comes to seahorses, such matchmaking is far from an exact science. Even under the most favorable circumstances, when the aquarist has carefully selected prime specimens of comparable size, one of the partners will still be rejected for no apparent reason in a certain percentage of the proposed pairings (Masonjones and Lewis, 1996).

For example, in one laboratory study of Hippocampus zosterae, 4 out of 19 pairs of seahorses specially selected for similarity of body size failed to court or mate (Masonjones and Lewis, 1996). This indicates that despite our best efforts, we can still expect roughly 1 out of 5 pairings to fail. So the bad news regarding seahorse compatibility is that the aquarist can do everything right and still fail to obtain a mated pair roughly 20% of the time. The good news is that such incompatibility problems are easy to overcome.

When your seahorses consistently fail to pair off despite your best efforts, there is one sure cure that seldom fails to put your breeders back on the fast track: simply add a new bachelor/bachelorette or two to the mix! Adding some fresh blood will almost always trigger a flurry of renewed activity and greetings as the seahorses reassess their shifting social dynamics and check out their prospective new partners (Giwojna, Jan. 1999). As an added bonus, the newcomers increase the genetic diversity of your herd and help prevent inbreeding, strengthening your seahorse’s gene pool.

The mere presence of a potential new rival (or rivals) will often stimulate the reluctant seahorses’ interest in courtship (Giwojna, Jan. 1999). Under such circumstances, just occasionally, seahorses may even end up bonding with partners they had formally rejected (Giwojna, Jan. 1999). It’s funny how an old beau can suddenly seem more attractive when your rival shows an interest in him.

Incompatibility is a much greater problem with wild seahorses than it is with gregarious farm-raised specimens. Captive-bred seahorses are simply not that picky when it comes to selecting mates. Put enough captive-bred Casanovas and frisky farmed-raised fillies together under favorable conditions, and the sparks are sure to fly!

Either way, whether it’s new pairings forming or former rejects reuniting, you can expect renewed interest in courtship and mating to result and your seahorses will soon reward your efforts with lots of breeding and babies.

Okay, Sean, that’s the quick rundown on encouraging your seahorses to breed and provide you with lots of babies on a regular basis. Judging from your description, it sounds like you have a compatible pair and that nutrition, water quality, incompatible tankmates, insufficient water depth, and stress are unlikely to be preventing breeding in your case.

But you may want to consider monitoring the calcium levels in your seahorse tank and adding a good source of bioavailable calcium, if necessary, as explained below:

Calcium (Ca): natural seawater has a calcium level of 400 mg/L and the seahorse keeper should strive to maintain the calcium level between 350-400 mg/L at all times.

Calcium is a very important element in the water in any marine aquarium and is a vital element in reef tanks. Along with carbonates and bicarbonates, it is required by calcifying organisms such as stony corals, snails and other mollusks, coralline, Halimeda and other calcareous algae, and certain sponges (Trevor-Jones, Apr. 2003). Calcium is a critical parameter for coral growth in reef aquariums, and chronically low levels will cause coral mortality and loss of coralline algae and
other invertebrate species.

Calcium reserves must therefore be replenished on a regular basis. Regular water changes may achieve this, but reef keepers may require the addition of biologically available calcium to maintain adequate levels (Trevor-Jones, Apr. 2003). Seahorse keepers should be aware that brooding males provide calcium to the developing fry in their pouches, which the embryos probably incorporate into their skeletons. Deficiencies in calcium could thus adversely affect your seahorses’ reproductive success and the health of the fry. In fact, seahorses that receive a diet deficient in calcium often suffer from decalcification of their exoskeleton, a debilitating condition commonly known as “soft plate” disease (Greco, 2004).

In addition to maintaining the calcium in your seahorse tank at the proper levels, Sean, I would also suggest providing your mated pair with a little competition to spice up their romance and help stimulate production of the key hormones that govern reproduction in Hippocampus. This would normally be accomplished by adding at least one other seahorse, either male or female, to provide your ponies with a choice of mates and a little healthy rivalry.

But you can sometimes accomplish the same thing by using the old mirror trick to give your seahorses the illusion that there is another pair nearby. Try taping a decent-sized mirror up against the aquarium glass where your ponies can get a good look at their reflections. Seahorses will often interact with their own reflections in the aquarium glass, so having a mirror-image seahorse that moves in response to his own actions can give the seahorse the impression that he or she has some competition, and that may trigger a little one-upmanship. It’s can be an effective technique for a situation like yours and can fool the resident seahorses into thinking they are actually in the presence of other seahorses that may try to beat their time. That may also be worth a try.

Finally, Sean, in the light of the problem you’re male had carried his pregnancy to full term the last time, let’s go over some of the factors that are known to influence the secretion of sex hormones and gestation one more time. As you know, sir, gestation may vary due to hormonal influences. 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

Some of the factors that influence these hormonal responses are the presence of the female, low oxygen levels, diet and, of course, stress. 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 (Vincent, 1990). 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 (Vincent, 1990). 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 (Vincent, 1990). The male is thought to further expand his pouch and develop the placenta-like internal structures to a greater degree as a result (Giwojna, Feb. 2002). More of the eggs can then be successfully implanted and carried to full term (Giwojna, Feb. 2002). 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. Consider monitoring the dissolved oxygen levels in your aquarium and make sure the tank has good circulation and surface agitation to facilitate gas exchange at the air/water interface and to promote good aeration and oxygenation.

Poor water quality — especially ammonia and/or nitrite spikes — are one of the most common aquarium stressors that can disrupt hormones and interrupt a pregnancy. Stress hormones such as cortisol will be released in response to such stressors, at the expense of other adrenal hormones, which can have a negative impact on the pregnancy and the developing fry.

Heat stress is doubly bad news for gravid males. Not only can abnormally warm temperatures disrupt the secretion of these key hormones and shut down breeding, they can also directly denature long chain polymers and macromolecules (e.g., proteins, enzymes and hormones) by altering certain bonds and changing the three-dimensional shape of the molecule on the atomic level. And, of course, water temperature also directly affect the metabolism of the seahorse and therefore its gestation period. Up to a certain point, increasing water temperatures will shorten the normal gestation period, just as decreasing water temperature will prolong or extend gestation.

Past a certain point, however, when the increasing temperatures exceed the comfort range for the seahorses, elevated temperatures will bring reproduction to an abrupt halt. For example, the Mexican population of H. ingens begins breeding in late September when the water temperatures decreases below 81°F (27°C), and keep breeding until late May when the water temperatures increase above 80°F again (Eliezer Zúñiga, pers. comm.).

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 (Tamaru, Aug. 2001). 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 actions of the aquarist and the aquarium conditions can have a big effect on how well a pregnancy progresses, and whether or not the fetal fry develop normally and are brought to full term, or are aborted, delivered prematurely, or resorbed as embryos. In short, Sean, it’s important to handle your stallion with care the next time he becomes pregnant, to keep him and his mate together, and to provide him with a nutritious diet, optimum dissolved oxygen levels, optimal water quality, and a stress-free environment at all times.

Best wishes with all your fishes, Sean! Here’s hoping your seahorses are soon reproducing and churning out brood after brood for you again.

Respectfully,
Pete Giwojna


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