difficulty acclimating pregnant Erectus

Dear Tom:

I think you on the right track, sir – I strongly suspect that the problem with your pregnant male is an oxygenation issue. As you can imagine, being deprived of oxygen really wipes a seahorse out, and the type of lethargic behavior you describe, with the affected animal being unable to hold itself upright and having to lay prostrate on the bottom for extended periods of time is very typical of seahorses that are not getting enough oxygen.

Seahorses are more vulnerable to low O2/high CO2 levels than most fishes because of their primitive gills. Unlike most teleost (bony) fishes, which have their gills arranged in sheaves like the pages of a book, seahorses have rudimentary gill arches with small powder-puff type gill filaments. Seahorses are said to have "tufted" gills because they appear to be hemispherical clumps of tissue on stems. Their unique, lobed gill filaments (lophobranchs) are arranged in grape-like clusters and have fewer lamellae than other teleost fishes. Because of the difference in the structure and efficiency of their gills, seahorses are unsually vulnernable to hypoxia when CO2 levels are high and/or O2 levels are low.

Gravid males are especially susceptible to low dissolved oxygen levels because they have an increased metabolic demand for oxygen as a result of their pregnancy. In your case, Tom, the gravid male was a new arrival that you had drip acclimated following long-distance shipping, and the stallion may therefore have been having a problem with methhemoglobin as well, further diminishing its ability to oxygenate its blood and transport oxygen through its body. I am thinking that that is why your new stallion was affected whereas none of the other seahorses suffered any adverse effects.

I suspect that your 110-gallon seahorse setup may be somewhat undercirculated, Tom, which may be contributing to the low levels of dissolved oxygen. In my experience, having too little water movement is a very common situation for home aquariums that house seahorses.

This is what I usually advise home hobbyists regarding the water flow in their seahorse tanks, sir:

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Water Circulation for the Seahorse tank

Many seahorse keepers are overly conscious of the inactive life style and limited swimming ability of Hippocampus, and have adjusted their flow rates accordingly, resulting in undercirculated tanks with too little water movement. That’s a serious mistake for a small, close-system aquarium.

In actuality, seahorses prefer moderate water movement, including some areas of brisk current, providing there are also sheltered spots and some areas of relatively slack water they can move to when desired. Slack water means comparatively low flow, NOT stagnant conditions! As with any aquarium, avoid dead spots and stagnant areas in the seahorse tank at all costs (Giwojna, unpublished text).

Contrary to popular opinion, seahorses are quite effective swimmers that can hold their own in strong currents as long as sheltered areas are available (Delbeek, Oct. 2001). I have often discussed this matter with professional divers and collectors who regularly encounter seahorses in the ocean, and they report that the horses are often found where you would least expect them — well offshore and thriving in areas with powerful currents. For example, here is how Paul Baldassano, a commercial diver in New York who makes his living collecting sea urchins, describes the behavior of his local seahorses:

"In regard to seahorses in the wild, I occasionally see Hippocampus erectus in the wild while SCUBA diving but never in the places where they are supposed to be. I see them in the open sea far from shore and also in areas with large rocks and very strong currents. The last one I saw was in a channel off the south shore of Long Island New York in water about 12 feet deep. The current was so strong that I had to hold on to the rocks so as not to be swept away. This Hippocampus erectus was having no trouble staying there munching on the abundant plankton. Apparently they find places near the rocks where there is no current because as you know they are lousy swimmers. There is also a large population of seahorses in a similar area in another part of the New York shore, but I think it is best not to divulge that location for obvious reasons (Baldassano, pers. com.)."

Neil Garrick-Maidment, a very successful seahorse breeder in the UK, reports much the same thing, noting that seahorses in the wild seem to thrive amid strong currents:

"Whenever I have dived on Seahorse sites I have always been amazed by the currents and tides that this very fragile looking Seahorse lives in. We often find Seahorses in flat muddy/silt areas nowhere near rocks or weed. These areas are often scoured by strong currents and the Seahorses do well in them and seem completely unperturbed by the current (Garrick-Maidment, pers. com.). In setting up a tank for them I try to remember the feeling I had in those areas and replicate them. I have now started to use wave surge devices, so that the current in the tank, although strong (they seem to thrive in strong currents) varies in its direction (Garrick-Maidment, Jun. 2002)."

Kirk Strawn, who earned his Master of Science thesis studying Hippocampus zosterae in the field, echoes Neil’s thoughts on the matter:

"The aquarist is not giving his seahorses natural conditions when he keeps them in a still-water aquarium. In nature tidal currents, wind, and waves are usually mixing the well aerated surface film water with the deeper water."

Likewise, David Warland, a fish farmer and commercial seahorse breeder in Port Lincoln, Australia, reports he often finds Hippocampus abdominalis perching on the tuna net enclosures at the farm in deep water:

"The Horses that are around the farms have traveled vast distances over plain sand/mud to get to the farms, which are in at least 20 meters of water, and are miles from the nearest land or shallow water (Warland, pers. com.)."

And Jorge Gomezjurado, the Senior Aquarist at the National Aquarium in Baltimore, recommends the following when it comes to water movement:

"I personally believe that current and water dynamics are very important for Syngnathids. In nature they live in areas with active water movement.(i.e., tides in mangrove lagoons and estuaries, coral reefs, kelp forests, etc.). Why don’t we give them the same environmental conditions in captivity? Our small tanks (90 gallons) have large turnovers on an average of 5 gpm (or 300 gph). It is very important that the current is steady and directionally constant, which allows the animals to find a good spot to hold and they will not be pulling in different directions all the time."

Most seahorse keepers feel it’s best to keep the current steady and nonvarying so they can find slack-water areas and sheltered spots downcurrent to hold in when they want to get out of the current. The more brisk the water flow, the more important this becomes. However, in a large aquarium with low to moderate water movement, alternating currents should not present much of a problem, and would help to provide good circulation throughout the tank.

The point is that, as long as slack-water retreats are available, the greater seahorses can tolerate far more current than most folks suspect and good circulation is as important for a seahorse setup as any other aquarium. What seahorses lack as swimmers is not agility, but rather stamina (Evans, 1998). They can hold their own against strong currents, but not indefinitely, so low flow areas where they can move out of the current and hold when they want to rest must be provided in addition to good circulation.

For example, along with an external power filter, my seahorse setup also has a 200 gph powerhead with a sponge pre-filter positioned right near the top for surface agitation and extra water movement, with additional small powerheads used as needed to eliminate any dead spots along the substrate or behind the rockwork. I like to give my seahorses as much current as they can handle without getting blown around.

In short, if your filtration is not turning over the entire volume of the aquarium a MINIMUM of 5 times per hour, your seahorse setup is undercirculated. With a spray bar return raised above the surface of the water to diffuse the outflow, you can safely achieved much higher turnover rates without producing too much turbulence or current for seahorses. A waterfall return is another good way to diffuse the output from your filter, and also works well for seahorses. There will be an area of relatively vigorous water movement at one end of the aquarium underneath and nearby the waterfall, while the other end of the tank is a relatively low flow area. (By the same token, however, if the filtration system in your seahorse tank is turning over the entire volume of water much more than five times per hour, it may be too overpowering for the seahorses unless it is diffused by a spray bar or waterfall return.)

As with anything, too much of even a good thing can be undesirable, and too much current can overwhelm the limited swimming ability of Hippocampus. One indication that you may have too much water movement in your seahorse tank is if the seahorses are getting buffeted around by the currents, and whisked away uncontrollably when they tire of fighting the current. Or alternatively, they may stay perched in one place all the time and refuse to swim around and explore their tank for fear of getting swept away by the current if they relax their grip on their hitching posts. So you can get a pretty good gauge of how well the seahorses are able to cope with the water movement than their tank by observing how the current affects the swimming ability.

Likewise, if a mated pair of seahorses is consistently spilling eggs during the copulatory rise, that’s another pretty good indication that there may be too much turbulence or water movement in the upper reaches of their aquarium.

If the seahorses are having difficulty tracking their prey and eating because the current whisks the frozen Mysis past them too quickly to target it accurately and slurp it up, that’s another red flag. Often that situation can be corrected simply by adjusting the output from your filter to reduce the current during feeding time or turning it off altogether while the seahorses are eating.

But as long as your seahorses aren’t getting buffeted around, aren’t routinely dropping eggs during disrupted mating attempts, and aren’t having difficulty targeting their prey and eating, there’s really no such thing as too much water movement. In general, the stronger the water flow, the more important it is to keep the water currents steady and unvarying so the seahorses can establish holding areas in the sheltered spots and low-flow zones without getting blindsided by unpredictable currents. Just make sure your seahorses are not getting trapped against overflows and be sure to screen off the intakes for any powerheads. Powerheads can be switched off at feeding time, if necessary.
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Okay, Tom, that’s my first impression regarding your problems with the new pregnant male. I am thinking that it is indeed a problem with low dissolved oxygen levels and/or high CO2 levels in your seahorse tank. Most likely, all you need to do to correct the situation is to increase the water flow and improve the circulation throughout your 110-gallon seahorse setup, taking care to provide good surface agitation to facilitate better oxygenation and promote better gas exchange at the air/water interface. Adding a good protein skimmer if the tank does not already have one may also be especially helpful for a situation such as this, because protein skimmers naturally increase the levels of dissolved oxygen in order to produce foam fractionation.

Best of luck with your pregnant stallion, sir!

Respectfully,
Pete Giwojna