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At any given time I have about ten or fifteen lined seahorses. This species (Hippocampus erectus) is one of the very few coldwater-tolerant varieties in the world. This particular type of seahorse is found in coastal waters of the western Atlantic Ocean from Nova Scotia to South America.

Although tough to keep alive in captivity, healthy ones will readily breed in an aquarium. Over the past ten years I’ve had roughly three or four thousand born in my tanks. Because the tiny young are so difficult to raise, I normally release my babies immediately into Narragansett Bay. I’ve noticed recently that the small, sheltered cove I’ve been putting mine in now has one of the largest seahorse populations in the bay.

Normally seahorses breed in the spring, but in captivity this fertile season can be extended throughout the summer and into the fall. Up until now mine haven’t bred in the winter, but this weekend one of my young males gave birth to about two dozen young. The usual clutch for a male seahorse is about 100 babies at a time. However two factors can cause smaller broods to occur. The first is a change in mate. Seahorses mate for life, and for some reason when a pair is separated the stress causes the number of young from a new pairing to be halved. Second is a young seahorse's first reproductive experience. This little male probably meets both of these conditions. I didn’t get a photo of dad, but here’s his new mate.

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The male seahorse has a brood pouch on his abdomen where the eggs incubate for several weeks before hatching. Once the eggs hatch, the young are ejected out of the pouch and released into the surrounding water. Although they are able to care for themselves, the young are very small. The ones pictured here are three days old and only about a quarter of an inch from the top of the head to the tip of the tail.

Even though seahorses are found in New England all year round, the water in the bay is much too cold right now for the young to be able to survive the transition into the wild. So I figured this would be a good time to try to raise some seahorse fry.

Baby seahorses need to start eating within an hour after being born. This means they must be removed from the parent’s aquarium and placed into a rearing tank. In the ocean they would start feeding on tiny planktonic crustaceans, so a substitute has to be on hand. The easiest food to grow are newly hatched Artemia, or brine shrimp. Dried shrimp eggs can be purchased from any pet shop, and when added to aerated water will hatch in a couple of days. These can then be fed to the seahorses. Because they can only eat a small amount at a time the plankton must be given to them at least six times a day. You can see the tiny Artemia this one is about to snap up near the bottom left corner.

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Sounds pretty simple, but there is a catch. Baby seahorses have very delicate immune systems, and brine shrimp egg capsules are covered with fungus and bacteria. This won’t harm an adult animal, but even a mild infection can wipe out an entire brood. To prevent this from happening the dried eggs are decapsulated before they hatch. This involves bathing the eggs in bleach and then washing them with a declorinator. If done correctly this will dissolve the protective protein covering of the eggs without killing the embryos inside.

One factor that dooms most seahorses born in captivity is air absorption. The young are buoyant and without proper water circulation they will drift to the surface and actually become trapped by the adhesive properties of water molecules. The same factor that allows water striders to glide across the surface of a pond traps baby seahorses to the surface where they slowly absorb air, rendering them helpless and unable to feed. The solution to this involves maintaining a circular water flow in the rearing tank and providing anchoring substrate for the little tails to wrap around.

Some tropical species of seahorses have non-hitching fry. Their babies are pelagic and simply drift with the currents until they are large enough to settle down on the bottom. The lined seahorse has hitching fry, meaning the young need to be able to grasp onto something within hours of birth. If a suitable substrate isn’t provided they will quickly die from exhaustion. I’ve found that plastic canvas from a craft store works great since it is fine enough for the tiny prehensile tails to grab on to, and because it’s made of smooth plastic it won’t cause abrasions on the delicate skin.

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One final note: A good survival rate, and one that is probably typical of those born in the wild as well, is four out of a hundred making it to a year old. Which means if just one seahorse in this brood is still alive this time next year we’ll have done extremely well. Although not pictured here, one of the babies is an albino. I’m rooting for her.

All photos by Rebecca Bray.

For more details on seahorse reproduction see my diary Dad Loves His Work. That post was followed up by Seahorses Part II.

Other diaries in this series can be found here.

Originally posted to Mark H on Thu Feb 05, 2009 at 04:58 PM PST.

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