Christopher:
First off, how did she get the laceration?  Was she attacked?  Is there something dangerous in the tank?  Or did she come with this wound?  This is a very important issue, as even healing the wound, if the source is not found, you could end up in this same predicament again.  Repetitive injuries to captive seahorses are huge stressors as well, and if this continues, you definitely run the risk of losing her to stress-related illness.  So, I leave it to you to ferret out the cause and resolve it.

It is almost impossible to tell if there is infection visually... an infected wound is white in color and often has hanging skin... so what you are seeing may or may not be an infected wound site.  You will want to take some preventative measures, though, just in case.

I couldn't agree with you more on not treating the tank if you don't have to.  I think this method of treatment is WAY over-recommended, and more often than not causes more harm than good.  Antibiotics are non-discriminating, and will therefore, decimate all of the beneficial bacteria in your bio-filter.  Most invertebrates do not handle antibiotics well either, so you run the risk of losing them and causing water chemistry problems from the resulting decomposition, or will need to remove all of them from the tank.  If you have live rock, you probably understand that this will be virtually impossible to do.  How do you remove that large sponge that you have not noticed because it is mostly contained within the cavities of a rock? Hospitalization is a much better option for treating with meds, but is a stressor for the fish, and often interferes with the healing process.  So, how can we help her with all of the odds stacked against us? Fortunately, you mentioned something in your arsenal that will allow us to safely treat your girl in her home, with little to no collateral damage to the tank in general.

Polysporin is one of my favorite secret weapons.  It is thick and gel-like so it tends to stick very well.  This topical medication is a mix of two powerful antibiotics and Lidocaine, which is a relatively strong analgesic.  Because of the consistency of the gel, you can safely use it in the tank without fear of destroying your inverts and bio-filter.  What you need to do is get her upside down so her head remains submerged but her wound is exposed.  Dry the wound with a paper towel, and then apply the Polysporin.  Do this over about three days, twice a day (am and pm), and she should heal up with no problems.  One thing though, be sure to have carbon running somewhere in your filtration system to absorb the dissolving meds.  This will ensure that the inverts and nitrifying bacteria are as minimally exposed as possible.

Best of luck!

Question:
I recently got my seahorses in (one month ago) and one was lying down in the bag.  The others looked fine.  I thought she needed to get in a tank and she would be fine.  I acclimated them and all are fine except her.  She eats every night, but is skinny.  She still lays on the sand some, but can get up and swim if she wants.  Just acts like her balance isn't right.  She will swim catch on something with her tail and lay down.  She seems to be breathing faster and harder than the others also.  Please help.  The other seahorses swim and stay by her side.  Thanks Tina

Christopher:
Hi Tina,
First, let me say that this is not a problem! Please do not think that you must treat your fish with meds or that she is suffering from some insidious disease.  Chances are she is just fine, but has a slight birth-defect, or more accurately, a post-natal developmental defect.

I must tip my hat to David and Tracy Warland from South Australia Seahorse Marine Services (www.saseahorse.com) for this tidbit of info.  It turns out that some fish, including seahorses, MUST fill their swim-bladder with air shortly after birth, which is why many seahorse fry are found stuck to surface of the water through adhesive forces of surface tension. They are gulping air to fill their swim-bladder.  The swim-bladder is a buoyancy control organ that allows some fish, like cardinalfish, to sit perfectly still, almost hovering in the water.  This means that the fish must expend less energy keeping itself upright and stable as it swims, as in seahorses.

Now, if there is a layer of protein or oil on the water surface, this impairs the ability of the little horse fry to get their snouts through the water's surface in order to gulp the air, and thus the swim-bladder does not get filled properly.  When this happens, the swim-bladder atrophies, and cannot be used to its full efficacy.  This can also happen if for some other reason the fry is not able to reach the surface to perform this function for whatever reason.

An atrophied swim-bladder results in a fish that cannot perform proper bouyancy functions, and will, therefore, swim at odd angles, fall through the water, and have a generally more difficult time locomoting.  This increased difficulty in swimming results in much more energy expending, and consequently the fish remains thin, much like a person with a very high metabolism who works out regularly.  No matter what that person eats, they will always be very thin and lean. I have had a horse like this for 2 years, and he is always a bit thin, but other than that healthy.  He has tried MANY times to mate, albeit unsuccessfully.  So, don't worry about and just love the dorky little bloke!