Emergency Seahorse Care Part III: Injections

By: | Date: 02/20/2004 | No Comments |
Editors Note 08/13/2015:
I no longer do injections on seahorses and would not without the guidance of a vet. I am keeping this article intact because I am aware that there are some people unable to access the aid of a veterinarian. However, this is a very invasive procedure, and really needs to be practiced under the care of someone with medical care.


Injecting medications is sometimes the only way you’re going to get an effective amount of medicine in a seahorse. Bath treatments often fail miserably because very little of the medicine is actually absorbed by the seahorse. Injections are even more important if the infection is internal.

Performing injections is dangerous. You may end up with an infection at the injection site, or other complications, such as overdoses. However, experience will teach you the best way to do it, and as you perform more injections you will get better at it. It is a risk, but like force feeding and sedating, there are times that taking the risk is the only chance of survival for the seahorse. And for the love of god, don’t stab yourself with a needle. I have no idea what medications would do to you, or especially a dirty needle since some diseases are zoonotic (can be transferred to humans).

You’ll need needles small enough to perform the injections. I prefer 29 gauge, but I have heard of 28 gauge being used on seahorses as well.

Antibiotic being drawn into a syringe.

Antibiotic being drawn into a syringe.

Obtaining medicine for injection can be tricky as well. If you can get a vet to help, all the better. DON’T — USE MEDICINE NOT MEANT FOR INJECTION. Crushing up a pill and adding it to sterile water is a bad idea. There may be additives that are safe in the digestive system but not injected directly into the tissue. If you can’t get a vet to prescribe the necessary medication, you’ll likely have to obtain it from a livestock store. Oxytetracycline is effective against many aquatic diseases. The problem is that most are concentrated for larger animals. What you will need to do then is dilute them to make it possible to actually measure the medication, otherwise the amount needed is so small its impossible to measure.

To find out how much medicine to use, you need to first know the correct dosage amount. If you’re lucky, its a drug that is commonly used for fish and you can find the recommended amount. If not, then you’re going to have to use established treatment regiments for other animals. For example, my bottle of Oxytetracycline says to use 5mg/lb. Then you will need to weight your seahorse. Weighing is quick so you shouldn’t need to sedate the seahorse for this. Place a shallow dish on the scale, zero it out (adjust the scale so that with the tray it is at 0) then quickly place the seahorse on it and get its weight. If you’re quick enough, the seahorse will only be out of the water for a few seconds.

"Dummy" seahorse being weighed.

"Dummy" seahorse being weighed.

Seahorse weight varies, but so far I’ve encountered seahorses as little as 8 grams and as big as 34 grams. For our example, we’ll say that the seahorse weighs 20 grams. Now, you must adjust the dosage to have a standard weight. I would convert pounds to grams. So you have
5mg/454g (rounded). That’s great, but how much to inject into the seahorse? To figure that out, you need to look at the equation:

5mg      Xmg
---  =   ---
454g     20g

X = .22mg. So, you need to administer .22mg of oxytetracycline to a 20 gram seahorse.

But, this is where it gets problematic and why you have to dilution. The concentration of oxytetracycline is 200mg per ml of liquid. That would mean, at the current concentration, you’d only be administering .0011ml of the antibiotic.

You aren’t going to find any syringes that go down to 10,000 of a milliliter!! Most small ones are graduated to either .01 or .02ml (cc). The way to achieve a concentration low enough to measure this is by dilution. YOu’re going to be attempting to reach a concentration low enough to measure. If we get it down to something like 10mg/ml, we will have a more manageable amount to work with. To determine exactly what concentration you want to dilute to, you will have to do some figuring here. We want it a small enough amount to not overwhelm the seahorse with liquid, but not so little we still can’t measure it. I would try doing the math on a few possible target dosages and see what made the most sense.

0.1mg       0.22mg
-----   =   -----
1ml          Xml
X=2.2ml -too much liquid

0.2mg       0.22mg
-----  =   -----
1ml          Xml
X=1.1ml -still too much

2mg         0.22mg
-----  =   -----
1ml          Xml
X=.11ml -better

4mg         0.22mg
-----  =   -----
1ml          Xml

x=.055ml better – I would then round up or down based on the medicines description (do the instructions say its it easy to overdose, or not?)

Now that we know the target, we need to dilute the stock so it’s a measurable amount. First we take the original concentration of 200mg/ml original concentration and do a serial dilution on the that is 10 in one. That’s 1 part medicine and 9 parts sterile water, i.e. 1 ml oxytetracycline and 9ml water, or .1ml oxytetracycline and .9ml sterile water.
That gives us 20mg/ml.
Now we need to do a more precise dilution using the following formula:
V1 C1 = V2 C2

V1 = volume of starting solution needed to make the new solution
C1 = concentration of starting solution
V2 = final volume of new solution
C2 = final concentration of new solution

(1ml)(20mg) = (4mg) (v2)

----------   =  V2

V2 = 5ml (The total volume of liquid in diluted solution)
Then subtract 1ml from 5 ml, which leaves you with 4ml of diluent. So to get the solution down to the target of 4mg/ml, add 1ml of the 20mg/1ml to 4ml of sterile water.

NOTE: Some of you may have noticed that you can do the V1 C1 = V2 C2 equations straight from the initial concentration, rather than diluting down to 20mg/ml. However, the serial dilutions are useful to do for the sake of precision. Unless you have extremely accurate tools, doing the equation from the initial concentration may end up with an incorrect solution. You would also waste a lot of sterile water for injection, which tends to be very expensive. In the above situation, you would have had to use 50ml of water. Or you’d have to start going into fractions of numbers, which could end up being confusing or easy to miscalculate.

Oops. No, I didn't do this on a seahorse, but accidentally to myself. Becareful with needles!

Oops. No, I didn't do this on a seahorse, but accidentally to myself. Becareful with needles!

Once you have the correct concentration, you’ll draw the medicine into the syringe. Its likely you’ll get air bubbles, which you don’t want, so usually draw in more medicine than you need. Then hold the syringe, needle end up, and tap the side until the bubbles rise to the center. Depress the plunger to release the bubbles (this is, in my opinion, the toughest part because the bubbles never go where you need them to to release them).

Now you’ve got your syringes ready, you can sedate the seahorse. Once sedated, you will hold it just below the water surface. You will inject in the underside of the tail, between the tail ring ridges.

Underside of tail, just below the body.

Underside of tail, just below the body.

Do it as high up on the tail as you can, with males it will need to be below the pouch area. You want to insert the needle at an angle, and only go a few mm in, just enough so that the whole tip goes in. The hole at the end of the needle is cut at an angle, so if you don’t go deep enough, you’ll end up just squirting it out into the water.

Here is where it gets tricky – MOST of the time, the needle goes in freely without resistance, some times it does not. I suspect this is due to the bony plating below the seahorses skin. If I encounter one of these areas, I remove the needle and move a mm or two away and try again. In one seahorse, I had to try 5 times before I had it go in smoothly. I was worried it would get infected because each time it was going through the skin, just not the plating. Fortunately, I’ve never had the injection (or attempted injection) sites get infected. Once it’s in, simply depress the plunger to inject the medication. Revive and the seahorse is all set.

Once again our "dummy" seahorse gets the abuse while demonstrating where to administer the injection

Once again our "dummy" seahorse gets the abuse while demonstrating where to administer the injection

Special thanks to Nadine who endured my endless questions on diluting medicine

On to Emergency Seahorse Care IV: CPR
Back to Emergency Seahorse Care Part II: Tube Feeding
Back to Emergency Seahorse Care Part I: Sedating

Document last updated 8/13/2015

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