Re:Seahorse Breathing Question

Dear Grant:

A simple rule of thumb to apply regarding the water depth required for seahorses to breed successfully is that most species require vertical swimming space equivalent to about three times their total length in order to accomplish the copulatory rise and transfer of the eggs comfortably, as discussed below:

Water Depth:

Some breeding projects are doomed to failure from the moment the aquarist picks out the aquarium for his seahorses (Giwojna, Jan. 1999). This can happen when a hobbyist selects a tank that is simply too shallow for the type of ‘horses he wants to raise (Giwojna, Jan. 1999). Seahorses are vertically oriented, and their upright swimming style is best suited to tall aquaria. More importantly, they rise vertically through the water column in order to mate, and if the aquarium is too shallow, they may be physically unable to copulate and transfer the female’s eggs into the male’s pouch for fertilization (Vincent. 1995b). This is an important consideration when breeding the largest species such as Hippocampus ingens, H. abdominalis, H. erectus and H. reidi. For instance, Australian breeders report that reducing the water level to below 500cm or about 20 inches deep can completely interrupt reproduction in Potbelly seahorses (H. abdominalis; Michael Dickson, pers. com.).

As a general rule of thumb, seahorses must have a minimum of 3 full body lengths of open water (top-to-bottom swimming space) above the substrate in order to mate comfortably (Giwojna, Jan. 1999). This will allow them to swim upwards for one or two full body lengths when they rise from the bottom and attempt to transfer the eggs. In other words, if you want to breed that prize 10-inch Potbelly seahorse of yours, you will need to provide him and his mate with a tank that is at about 30-inches tall (Giwojna, Jan. 1999). Or, in order for a pair of 6 inch Mustangs to mate comfortably, you should provide them with 18 inches of unencumbered swimming space.

When selecting a breeding tank, bear in mind that the ”three-body-lengths” rule applies to the depth of the water in the aquarium, not the height of the tank per se (Giwojna, Jan. 1999). If you keep the water level in the tank an inch from the top and have an inch of calcareous gravel or crushed coral on the bottom, a 12-inch tall aquarium only has 10 inches of vertical swimming space. With such a tank, the hobbyist would thus be restricted to one of the smaller seahorse species that attain an adult height of no more than about 3 inches from the tip of their coronet to the tip of their tail. For example, a pair of 6 inch Hippocampus erectus may have difficulty mating in a tank that is only 16-inches high, since they need around 18 inches of vertical swimming space for the copulatory rise, and you must account for the air space at the top of the tank as well as the depth of the substrate (Giwojna, Jan. 1999).

This is where your 14-gallon Biocube is problematic, Grant. Those tanks are a bit less than 17 inches (16.7") tall to begin with, and if you have your mini reef established with a deep live sand bed (DLSB), you will have 3 or 4 inches of sand on the bottom plus a 1 inch air gap at the top of the tank, meaning the water depth of the tank is only 12-13 inches at best. And that’s in an area of the aquarium where there would be no live rock or corals or decorations of any kind above the level of the sand bed, which probably is a situation that does not even exist in a nano reef which is chock-full of life.

The urge to breed is very strong in Hippocampus, however, and if kept in a shallow tank, pairs will do their best to improvise, adapt, and overcome such depth limitations. I have seen experienced pairs whose copulatory "rise" was more horizontal than vertical due to a lack of water depth, yet which eventually managed to mate successfully. Typically, the shallower the tank, the more difficult coitus is to achieve and the more likely it becomes that eggs will be spilled during the transfer. Eventually this reaches the point where entire clutches are being lost, which is when most pairs cease trying and no longer attempt to breed (Giwojna, Jan. 1999).

Worse still, shallow tanks increase the danger that an overripe female may become egg bound. In a tank with inadequate water depth, a courting female that has hydrated her clutch may be unable to make the egg transfer, yet she will be reluctant to dump the eggs while a receptive male is still standing by eager to receive them. If she is overly optimistic and retains her clutch too long, hoping to pull off the tricky egg transfer despite the lack of depth, she may become egg bound. Her lower abdomen will become very swollen and prolapsed tissue may protrude through the vent as the pressure builds up. If she is unable to release the eggs at this point and relieve the pressure, death will result. An egg-bound female is thus a very serious complication of depth limitations (Leslie Leddo, pers. com.).

Worst of all, even if the seahorses can manage to mate successfully in your Biocube, we are still disregarding the more serious problem of gas bubble syndrome (GBS). As you know, the shallower the aquarium, the more likely chronic problems with GBS are to occur, which is a very dangerous situation because GBS is a fatal condition if untreated. In a nutshell, large seahorses in aquariums less than 20 inches tall are very susceptible to various forms of gas bubble syndrome. So in a 14-gallon Biocube set up as a mini reef, which may have only 12-13 inches of water depth, seahorses will be predisposed to problems with GBS in the long run.

As I said before, you may certainly add another seahorse to your 14-gallon Biocube to keep your female company, even if they don’t mate successfully, but to do so will not be conducive to the long-term health of the seahorses due to the increased risk of egg binding and the likelihood that chronic problems with GBS will develop sooner or later. The small Gulf pipefish we discussed earlier are a much better bet for your particular system, sir.

There is only one species of seahorse that can be found in the coastal waters of North Carolina, and that is the lined seahorse (Hippocampus erectus), Grant. That is one of the larger species that can grow to well over 6 inches in length at maturity, so it is not a good candidate at all for a 14-gallon Biocube. A juvenile specimen may be comfortable in such an aquarium for a matter of months, but H. erectus normally achieves its maximum size at an age of 6-12 months, so the long-term prospects for such seahorses in a small tank like yours are very poor.

Yes, pregnant males are likely to pair up eventually with an available female of the same species at some point after they deliver their brood. They do not remain faithful to an absentee partner indefinitely. They will often miss the next breeding cycle (usually about a month) waiting to see if their missing partner reappears, but usually begin to seek out a new mate in the subsequent months. But, as I said, I would not count on any breeding taking place in a shallow tank like yours, and adding a mature male from a large species like H. erectus would be over stocking your mini reef and increasing the bioload in the tank to a precarious level.

The problem of algae growing on your seahorse is a common occurrence, especially in shallow aquariums with high-intensity lighting such as your nano reef, Grant. Algae often grows on the exoskeleton of seahorses, typically on their head and neck which are closest to the light source. That’s perfectly normal and nothing at all to be concerned about. Seahorses often encourage algae to grow on them as a protective device to enhance their camouflage, and it’s often best simply to ignore any such growth.

We are all well aware that seahorses can change color to blend into their backgrounds, and that Hippocampus is capable of growing or shedding dermal cirri, which are long filaments and branching extensions of its skin, as called for in order to match its environment. To complete its disguise, the seahorse allows algae, bryozoans and other encrusting organisms to grow on its body, thereby rendering it all but invisible in its natural habitat. In fact, its skin contains polysaccharides which are believed to encourage algal growth, thereby helping it disappear into its surroundings. This vanishing act is so convincing that, even when they are collected by hand seining, seahorses often go undetected amidst the plant matter that accumulates in the net. Unless the collector is really diligent, he will lose a large proportion of his catch simply because many specimens will be overlooked and thrown back with the debris. In short, it’s perfectly normal for algae to grow on seahorses.

If you find the algae growth to be unsightly, you can certainly brush it off using a soft camel’s hair artist’s paint brush. Just be very careful when you are handling the seahorse and gently brushing away the algae so that you don’t remove any of the seahorse’s protective slime coat if you can possibly avoid it.

The seahorse’s pliant skin or integument is of course its first line of defense against disease. It contains mucus glands, and the slime covering the skin acts as a barrier to ectoparasites and infection. The protective slime can contain antibodies and antibacterial substances, and excessive mucus production is often the first sign of an infection or parasite problem. On the other hand, healthy seahorses often have small bright dots on their heads and torsos, which are actually mucus deposits. These beads of mucus glisten like little diamonds and are a sign of vibrant good health. When handling a seahorse, it’s important to wet your hands first in order to avoid removing too much of the protective slime coat.

Marine fish are always in danger of dehydration because the seawater they live in is saltier than their blood and internal body fluids. As a result, they are constantly losing water by diffusion (osmosis) through their gills and the surface of their skin, as well as in their urine. The mucus layer acts as a barrier against this, waterproofing the skin and reducing the amount of water that can diffuse across its surface.

So feel free to very gently brush away the algae as long as you take the necessary precautions and don’t disturb your seahorses’s protective slime coat any more than necessary, but you should be aware that the algae is very likely to regrow if you don’t also address the conditions that are promoting the algae growth. Reducing the photoperiod and/or switching to fluorescent lights or a combination of fluorescent and actinic bulbs would help to eliminate the algae growths on your seahorse, but adjusting the light levels in your reef tank may not be an option. However, mushrooms and soft corals usually don’t require high-intensity lighting, so reducing the photoperiod and intensity of the lighting would be the first option I would explore.

Best of luck with your 14-gallon nano reef, Grant!

Respectfully,
Pete Giwojna