Dear Sherry:

Pete Giwojna

Dear Sherry:

In the wild, the breeding season for our native American H. erectus begins in April and lasts until the seahorses move into deep water with the onset of winter. So the heart of the breeding season is during the warm summer months, whereas late fall and winter are normally the off-season.

But the Southern populations of erectus (in Florida, the Gulf of Mexico, and parts of Central America) may breed year-round in the wild, and that’s also often the case when they are kept under aquarium conditions, although breeding still may taper off during the winter months.

With highly domesticated cultured seahorses such as Ocean Rider Mustangs and Sunbursts (Hippocampus erectus), which have been born and raised in captivity for many generations, it is pretty typical for the ponies to continue to breed year-round in the aquarium.

If you’re breeding pair is producing more fry then you can keep up with, Sherry, you may want to try gradually adjusting your aquarium conditions, especially the amount of time you keep the aquarium lighted every day, as discussed below:

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 and 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, as explained in more detail below by Steven Young, the Aquarium Biologist at the Seattle Aquarium, Sherry:

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 (natural seawater), we get fluctuations from 26-31ppt depending on rainfall.

Steven Yong
Aquarium Biologist
AZA PMP Leader and Studbook Keeper – Lined Seahorse
Seattle Aquarium

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 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 if you are hoping to curb the romantic tendencies of your Hippocampus erectus, Sherry – 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 usually very effective in shutting down the breeding of wild-caught seahorses, Sherry, and it may also work well for you.

Of course, unless you have an aquarium chiller, it is very difficult for the home hobbyist to gradually reduce the water temperature in order to simulate seasonal changes, Sherry. But it’s the photoperiod or light-and-dark cycle that is the primary key to regulating breeding in many tropical seahorses, and the home aquarist can easily adjust his or her aquarium lighting.

In my experience, the photoperiod of the aquarium – the length of time the aquarium is lighted each day – has a much more profound effect on the breeding behavior of tropical seahorses in captivity than water temperatures within the range of 72°F-78°F or so. In a nutshell, seahorses breed best when provided with a photoperiod of at least 12 hours a day, and providing your ponies with significantly less light each day can inhibit breeding.

But in order for this to work, the aquarium cannot be situated where it will be receiving natural sunlight from the windows in your fishroom, or the hours of daylight will have a bearing in addition to the time the aquarium lights are left on…

Best of luck with your prolific ponies, Sherry! Here’s hoping the survivorship rates of the newborns continues to improve with each subsequent brood as you gain more experience at rearing.

Pete Giwojna, Ocean Rider Tech Support

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