Fry Development Cycle - From Egg to Horse

By Mike Gilbert and Bethany Watson

The following images all come from dropped eggs or stillborn embryos:

Eggs

Four eggs dropped from female

Eggs are cone shaped, approx. 3/32" in length

Birth Defects

Siamese twin taken after specimen died

Development of an Embryo:

The egg is deposited in the male's pouch and fertilized:

Stage 1

At this point the embryo is developing recognizable characteristics such as a snout, eyes, body, and tail. However, it still resembles an egg more than a seahorse:

Stage 2

At stage 3, the features of a seahorse embryo become far more recognizable. You can clearly see detailed eyes, a developing (albeit short) snout, and the tail is beginning to appear at the base of the body of the embryo. You can also still clearly make out the embryonic "sac" that is around the baby:

Stage 3

At stage 4 the seahorse has eyes that are easily distinguished, and you can clearly see that the snout is beginning to "cleave" or split to form the upper and lower half. Their internal organs are beginning to develop (as seen in the many red spots), and the tail is more pronounced. The big "belly" they seem to have is pink and looks like a part of their yolk sac:

Stage 4

At stage 5 the seahorse has eyes that are readily distinguished and very large, and you can clearly see that the snout is beginning to fully "cleave" or split to form the upper and lower half. They are significantly bigger in size, and you can see their body, tail, and even their dorsal fin when you look closely at them. Upon observation under a microscope or a magnifying glass, you can also see other distinguishing features such as their heart, gills, and air bladder:

Stage 5

At stage 6, their snouts are fully cleaved, but still blunt and short. As you can see, their "triggers" are developing, and their eyes are clear and more in proportion. Under a microscope or magnifying glass, you can see their fins, internal organs, and spinal column. Their tail is long. As you can see, they are still very pink, and "yolky" looking in their bodies:

Stage 6

This is a picture of a fully developed baby Hippocampus reidi as seen under the macro lens of our camera. As you can see, it is fully developed and has a snout that is to length and cleaved, eyes that are more in proportion to its head, etc. Under a magnifying glass, you can see the internal organs such as the heart, gills, and spinal column. The red line that runs the length of the body vertically may be one of its main arteries. These babies even have the beginnings of a small crown developing when they are born, and are also born with spines (ouch!) on their body. Structurally, they are a perfect replica of their adult parents in a much smaller form.

Fully Developed

Rearing: Tank Design

Designing your rearing system can be a real challenge or a simple task depending on what type of fry you're working with. I've tried several designs and setups for H. reidi, as they seem to be the most difficult species I've encountered to raise. My current system is the culmination of many hours and alot of work but seems to work well consistently. Below I've shown just a few of the possible designs, the ones that work for us. By no means are theses the ultimate setups or the only way to go. The main things to remember are to provide the best environment possible. Power filters may become death traps as can the wrong type of foam used on a drain. As each brood comes you make improvements to your system until it's perfect (haven't got there yet :-).

Option 1: The Simple System

The simplest rearing tank is simply a plain square with a heater, foam filter, and something for the fry to hold onto. The above tank is actually a ten gallon with dividers siliconed in to make three tanks. The orange square seen inside on the left is "plastic canvas" available at most craft stores and is a favorite to grab onto at night. This type of system works well for most species. As a rule of thumb if the seahorse can hitch (grab onto something) right after birth they most likely can be reared in this system.

Option 2: The Advanced System

This system is more involved both in construction and function. Focusing on Hippocampus reidi as a reference species, this tank works very well. This system consists of a 3.5 gallon rectangular tank equipped with drip bars along the edges to create surface turbulence. This prevents small fry from getting stuck on the sides of the tank. This system also features a flow through design, where as the water is pumped into the tank from a wet/dry filter below and returned through a drain in the bottom of the rearing tank. In addition to the wet/dry filter it also utilizes an 8 watt UV sterilizer as well as a 5 micron mechanical filter.

Option 3: The Green Tank

Although I have not experimented much with this method, I have raised a few fry with just a tank of green water. This type of system is simply a tank set up in a well lit area and seeded with copepods once the micro algae has taken off. The micro algae acts as the filtration. I've had a few H. kuda fry at one point that were lying on the bottom of the rearing tank not doing well so we decided to try just putting them into a tank of green water with some copepods. We just kind of forgot about it until one day I saw three pairs of eyes peeking out at us. The algae culture started crashing eventually so I took them out and raised them as usual.

Raising the Fry

Once you have your rearing tank setup you're ready for the babies. I'll basically discuss dealing with H. reidi fry as they are the most sensitive and the topics covered can be applied to any species. There are three basic things to remember when raising fry other than having quality fry to begin with. They are described below.

Factor 1: Water Quality

The first factor is water quality. H. reidi fry is very picky when it comes to this, but not as picky as you may think. The most important aspect other than your basics is pathogens. You can have the best water quality possible but if there are parasites eating holes through your fry or bacteria infecting them it doesn't matter. So how do you know if you have parasites?  Things to watch for are excessive twitching, grabbing themselves with their tail like they're scratching at something (they usually are). The most effective treatment for the parasites that have attacked the fry is formalin at a quarter or half the recommended dose. The fry tolerate it very well, and it won't hurt them any more than the parasites. Beware however that any invertebrates such as snails, etc. won't like it either and it can actually kill them. Copepods tolerate it well however. Temperature is best around 80F. They do fine at a specific gravity of 1.024. As a point of note you can lower the specific gravity to as low as 1.011. This lower level inhibits some of the bacteria and parasites and lessens the stress on the babies. I lower it over 2 days usually. Lower it gradually so they don't go into shock. And I also raise it gradually for the same reason. My reidis typically grow to 4–5 times the size they were when they were born by week one, with survival rates in the 90% range. Of course there are other factors, but this is an important one. By the way I also use synthetic sea water and we live at the base of the mountains, so it is possible to raise these guys without natural sea water. Bacteria can usually be controlled with a slight dose of methylene blue. A recent batch of H. fuscus were dropping like flies until one drop of methylene blue and 1/4 tsp. formalin were added. A week later I have not lost any.

Factor 2: Food Quality

The second factor is food quality. This is where it can get really tough. Brazilian fry is famous for not eating, eating then dying, etc. Unless you have no other options they shouldn't eat baby brine until week 2. There is something about it that clogs them up or gives them some severe problems. The biggest problem is that it just plain isn't nutritious enough for them to develop on. If you must feed them brine your best bet is with very newly hatched, such as under 2 hours old. Decapsulating the cysts will also help as the brine won't use up all their energy reserves breaking out of the cysts. For details on decapsulating I have the procedure outlined here.

Of course other species can do well on newly hatched artemia, just be sure to enrich it with a HUFA booster prior to feeding. For more on enrichment click here.

Rotifers are the next most common food offered. In order to have a good chance with them you'll need to enrich them first also. It's also a good idea to rinse them before feeding, which is an art in itself.

The absolute best food for reidi fry in our opinion is copepods. Larval or not doesn't matter. I've seen a reidi only a few hours old scarf down a full grown copepod larger than a newly hatched brine shrimp, which only adds to the mystery of brine killing them. Copepods don't need to be enriched, they are naturally high in fats, lipids, and waxy esters. For more information on culturing copepods click here.

I feed our broods twice a day,  once in the morning and once at night. They seem to do just fine on this schedule and I believe it's actually beneficial as it gives them time to digest their food.

Factor 3: Environment

The third factor is tank and environment. In the wild H. reidi fry most likely float amongst the plankton layers. I assume this because they don't hitch until two weeks old when they are developing in our tanks. This presents all sorts of problems. In the ocean there are no glass walls to crash into. I've tried several tank designs, some just plain crazy. My current system is the one outlined above as the Advanced System. Most other species will do fine in the Simple System and this is all that is necessary.

4 week old H. reidi

With alot of patience and a little luck you'll be up to your ears in seahorses :-)  I'll add more soon regarding getting them onto frozen food, development, etc. In the mean time feel free to contact me if you have any questions or comments.

Most recent revision: 2002

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Mike Gilbert, Bethany Watson & Seahorse.org
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Seahorse fact: Most seahorses are found in shallow waters.
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