Keeping a single-sex herd?

Dear Darrell:

That’s a good question and it deserves a thorough response, since I know there are many home hobbyists like yourself, Darrell, who are either unprepared or unequipped to attempt raising the young.

Under those circumstances, there are three good options that will prevent the seahorses from breeding or enable you to adopt out any offspring they produce to other hobbyists:

(1) You can segregate the sexes to prevent the seahorses from reproducing, and keep either all females or all male seahorses in your aquarium.

(2) You can keep a mated pair of seahorses and allow them to breed freely, but then disburse the babies to other hobbyists in your area that would like to try their luck at raising seahorses.

(3) You can keep a mated pair of seahorses in your aquarium and then manipulate the environmental cues – especially the photoperiod – in order to prevent your male and female from breeding.

Let’s discuss these three options in greater detail below, sir.

It is certainly possible to keep seahorses successfully in a same-sex setup, Darrell, and a number of home hobbyists do so for various reasons. The highly domesticated Ocean Rider Mustangs and Sunbursts (Hippocampus erectus) are typically very gregarious, sociable animals that very much appreciate the company of others of their kind, so a tank that houses only only males or females is doable. The females are subject to fewer health problems in many cases, because they lack a heavily vascularized brood pouch and never suffer from any of the complications of pregnancy, but even in the wild, the normal social unit for both seahorses is the mated pair, and I am much less certain as to whether the seahorses are truly happy when the sexes are segregated over the long term…

So although it isn’t necessary to keep seahorses in pairs, I do feel that seahorses are happier and healthier if they have a chance to court and breed, which I think is just as true for us seahorse keepers as it is for our charges. The seahorses certainly enjoy a richer, more natural life when they have the opportunity to interact, court one another, pair up and reproduce. And maintaining a mated pair allows the hobbyist to witness the fascinating courtship displays and mating dance of the seahorses – one of the grandest spectacles a home aquarist will ever be privy to!

Over a period of days, the partners perform a series of ritualized maneuvers and distinct displays — brightening, reciprocal quivering, pumping, pointing, and several delightful dancelike displays (the carousel dance, Maypole dance, and the parallel promenade) — all culminating in the copulatory rise and exchange of eggs. Once a pair has bonded, these maneuvers are repeated regularly in a daily greeting ritual that strengthens and reinforces the pair bond. In my opinion, the seahorses have a better quality of life when they are allowed to engage in these activities in the aquarium, even if it means sacrificing their young.

In short, keeping mated pairs provides behavioral enrichment for the seahorses and they are happier and healthier as a result. Not only is it good for the seahorses, it’s also fascinating for the fishkeeper to observe their social interactions and charming courtship rituals.

A group of males can also be kept together successfully if necessary, and maintaining a group of stallions together often makes for a very entertaining exhibit and allows the aquarist to observe dynamic social interactions that do not take place when a group of females are confined together. For example, the urge to reproduce is very strong in the young studs and they will often go through all the motions of early stage courtship, even when confined with other stallions. This includes brightening, head tucking, and quivering, as well as some of the dancelike displays.

It’s not uncommon to see same-sex courting behavior or even homosexual mating attempts in male seahorses maintained in the same-sex environment. Even solitary males often go through the motions of courtship when there are no other seahorses present in their aquarium (Abbott, 2003). They may court their own reflection and sometimes even direct their courtship displays toward their keepers (Abbott, 2003). If no females are present, over-stimulated stallions will sometimes soothe themselves by basking in the air stream from an airstone, content with the tactile stimulation provided by the gentle barrage of bubbles. They may even flirt with inanimate objects. If all else fails, a hitching post may actually suffice as a suitable surrogate when no better alternative is available (Abbott, 2003)!

In addition to courtship activities between the irrepressible males, the aquarist is also often privileged to witness competitive behaviors between the stallions that are not displayed among females, Darrell. This includes sparring, headbutting, and tail wrestling as the males sort out a dominance hierarchy of sorts, all of which are fascinating to observe. I should emphasize that such competitive behaviors are highly ritualized in Hippocampus. The idea behind such harmless tussles is to assert dominance, not inflict bodily harm. Tail wrestling and snapping are forms of ritual combat — little more than glorified shoving matches and tug of wars — with clear-cut submission signals that are always honored. They seldom do any real damage and the combatants are so well protected that serious injuries are virtually unknown when these armor-plated adversaries throw down the gauntlet. In short, intrasexual competition among the stallions in a same-sex tank can sometimes be intense, but it’s normally nothing to be concerned about and is always extremely interesting to observe. However, when males are segregated from females for a long period, there tends to be an increase in such aggression and a corresponding increase in stress levels.

There is also a slightly increased risk of egg binding when females are kept in a same-sex environment, but I wouldn’t let that deter you. Egg binding is quite uncommon and I have only seen or heard of a handful of cases in all my years, so the risk is really rather remote. In the vast majority of cases, even if a female should ripen a clutch of eggs in the absence of any receptive males — which in itself would be quite unusual — she normally will not hesitate to drop a clutch of ripe eggs and spill them on the bottom of the tank when there are no stallions present.

All things considered, it is generally preferable to obtain pairs of ponies, Darrell. If you are concerned that the pair-bonded seahorses will produce babies that you are unprepared to deal with, there are usually better ways to deal with that possibility than segregating the sexes.

First and foremost, Ocean Rider allows hobbyists to freely disburse their fry any way they see fit up until they reach the age of 30 days. If they are overburdened with a baby boom, the best bet for most hobbyists is therefore to adopt the newborns out to surrogate parents who live within driving distance. Of course, this works best if they have a friend or neighbor or know a fish guy down at your LFS who are interested in rearing and can take the excess fry off your hands. It is more difficult to ship seahorse fry to interested parties long distance and the newborns often don’t tolerate long-distance shipping well.

But for the hobbyist whose only other recourse is to euthanize the fry and sacrifice the entire brood, shipping newborn fry overnight is still preferable to the alternative. However, shipping is definitely a better option for fry that have grown a little. Seahorse fry that are 2-4 weeks old are tougher and withstand shipping much better than newborns. (This is true when it comes to disease treatments as well; once fry have reached the age of 2-4 weeks, the can generally tolerate the same medications/chemotherapeutics and treatments as the adults.) So once your fry have reached 2-4 weeks, you can ship them off to surrogate parents if need be and clear out your nursery tanks just in time for your seahorses’ next brood.

If there is a Marine Aquarium Society in your area, Darrell, you can bet that they will have members who would love to get their hands on some of Mustang or Sunburst babies and take a crack at rearing them if your pair of ponies proved to be prolific breeders. In most cases, that’s an excellent option and worth a try when it comes to distributing the offspring from a new brood of babies.

If dispersing the young to surrogate parents is not a practical alternative for you, Darrell, then I am told that it is relatively easy to alter the photoperiod and water temperature in your seahorse tank in order to mimic seasonal cues in order to shut down the breeding behavior in your ponies. To be more specific, if you gradually drop the water temperature (no more than 2°F per day) to as low as 68°F-72°F, if possible, and provide the seahorses no more than eight hours of light each day, you can in effect duplicate the seasonal cues that cause the seahorses to lose interest in courtship and mating after the breeding season has passed.

I have never tried manipulating the environmental cues in order to prevent my ponies from breeding, since I’m always happy to have another brood of babies on my hands. (If I don’t have the time for rearing personally, I have lots of friends who love to serve as surrogate parents when I have a surplus of babies.) But if you deny the seahorses sufficient daylight and keep their aquarium darkened long enough each day, that should shut down the production of key hormones and prevent your seahorses from breeding, Darrell, as explained in more detail below by Steven Young, the Aquarium Biologist at the Seattle Aquarium, Darrell:

I haven’t altered temp and lighting seasonally but I have done so to control mating behaviour in my erectus. I’ll usually drop temps down to 74 and light cycle to 10 hrs when I don’t want mating. Normal parameters are 78 and 12 hrs. I don’t do much in terms of salinity, but since we do use NSW, we get fluctuations from 26-31ppt depending on rainfall.

Steven Yong
Aquarium Biologist
AZA PMP Leader and Studbook Keeper – Lined Seahorse
Seattle Aquarium
1483 Alaskan Way, Pier 59
Seattle, WA 98101
.

To understand why the photoperiod is so important for regulating breeding, 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 selectee: through or 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). So that’s something to keep in mind when you are hoping to curb the romantic tendencies of your Hippocampus erectus, Darrell – you need to make sure that the main tank is darkened enough to trigger the secretion of melatonin by the pineal gland in response to the hours of darkness.

Manipulating the seasonal cues in this way is very effective in shutting down the breeding of wild-caught seahorses, Darrell, and it would probably work well for you.

Finally, I should also point out that most seahorse breeders, including Ocean Rider, prefer to sell seahorses as mated pairs. For one thing, most of their customers want male/female pairs and many home aquarists look forward to the challenge of breeding and raising their ponies. Indeed, for some hobbyists, the primary appeal of seahorses is the relatively ease with which they can be bred and raised under aquarium conditions.

I’m sure you can understand that is therefore undesirable for the aquaculture facility or supplier of seahorses to be left with a heavy preponderance of either males or females. For this reason, and due to the factors we discussed earlier, seahorse breeders may be reluctant to fill large orders that specify that all of the seahorses must either be males or females.

Okay, Darrell, those are some things to keep in mind when deciding whether or not to order pairs of ponies or to stick with a same-sex seahorse setup.

Best wishes with all your fishes, sir.

Respectfully,
Pete Giwojna, Ocean Rider Tech Support