Reply To: Seahorse Breeding

Pete Giwojna

Dear Car Doc:

Dwarf seahorses (Hippocampus zosterae) are prolific breeders and if you provide the newborns with a nutritious diet, good water quality, and suitable conditions then is likely that they will also pair up and breed when they mature.

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:

<open quote>
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
<close quote>.

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, Tim – 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, Car Doc, and it would probably work with your pigmy seahorses if you can maintain the right conditions (reducing the water temperature and shortening the hours of daylight in the aquarium).

Good luck.

Pete Giwojna, Ocean Rider Tech Support

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