All Things koi and H2O


Give it a shot


Duncan Griffiths


This short article is to give an insight into the possible injection sites and some of the more popular injection methods for koi.

There are three main ways to inject an antibiotic

IM, intramuscularly

IP, Intraperitoneally

IV, Intravenous

We will take the last first, IV, Intravenous,

IV, Intravenous as the name implies involves delivering the medication into a vein of the fish, this involves an injection site under the caudal peduncle just ahead of the caudal fin.
The main vein run directly under the spinal column, so the needle is inserted vertically at this point until it comes up under the spine and actually very lightly hits the spine, at this point the syringe is withdrawn away from the spine a very minute distance about 1ml the actual point of the syringe should now be in the vein.

A slight pull back on the syringe plunger should draw blood into the main body of the syringe, this is an indicator that you are in the exact spot needed and at this point you should depress the plunger and deliver the medication.

It has to be mentioned this is not a well-practised protocol for many reasons all of which should be apparent, and is not recommended for the amateur fish fixer.

  1. Small fishes do not adept well to this method
  2. Possible Damage to the spine
  3. a possibility of a severed vein
  4. A very definite need to anaesthetise the koi
  5. Not a very easy technique to master


x marks the spot for an Intravenous injection




This leaves two methods for our purpose IM and IP injections



There is much debate over these two mainstream methods of injecting, which type is better and more effective than the other.

IP is considered the better method in the USA, where as IM is by far the common practice in the UK.

There is only one site for an intraperitoneal injections, that is midway between the anal fin and the ventral fins and further involves turning the koi upside down, so more often than not anaesthetic is involved, in order to avoid handling damage and needle damage if the koi were to move whilst the injection process is taking place.

IP or intraperitoneal injections involve delivering the antibiotic injection into the stomach cavity of the fish, there it is absorbed into the blood stream very quickly indeed, this is said to be a more effective way to deliver the medication over IM injections. There may be some element of truth to this, but this is to do with the way the koiís blood circulation works.

IM or intramuscular injections given into the muscle, the substance ie,antibiotics given this way diffuses into the tissue and then into the blood stream, then the circulation of the substance begins, trouble with this is, antibiotics circulating in this way have to go through the kidney, which in itself is a sieve for impurities and as the antibiotic itself is an impurity the kidney may purge some of its usefulness out of the blood stream to waste.
IP injections given into the stomach cavity and diffusing into the blood stream do not go this route through the kidney, with obvious benefits

But its not all good news for IP injections, as there is an abundant flora of beneficial bacteria living in the koiís gut that aid digestion, the first port of call to an injected substance given the IP route is the gut and this self same bacteria. We cannot afford to destroy these beneficial digestive bacteria.

Additionally with IP injections, there is a slight risk of damage to a major organ or a puncture to the intestine with fatal consequences

However,for those who, practice IP injections, such occasions are very rare.


Anaesthetise the koi once the koi is calm, turn it upside down, this has the effect of allowing the internal organs to drop down in the stomach cavity in the direction of the spinal column, thus out of the way of the impending intrusion of the syringe needle.
Draw and imaginary line between the vent and the ventral fin,down the centre line of the fish

Pick a spot midway between these two points and begin to place the needle, at this point before inserting the syringe in to the abdomen, move the needle about 2 ml off the centre line, this avoids a very hard piece of cartilage running dead centre, either side of centre line is OK, pointing the syringe forward at a very shallow angle, as thought, if the needle were long enough it would emerge out of the koiís mouth. insert the needle keeping the needle running just under the skin, once most of the needle is inserted try a depress the syringe plunger down if resistance is met push the needle in a little further till the plunger moves easilyand fluid runs out. If resistance is still encountered, back the needle out a little then very slightly increase the angle of the injection, but not to much and try again.
T his type of inject is unlike IM injections, when the right spot is obtained the fluid in the syringe will move out into the abdomen with little or no resistance.


IM, intramuscularly.

There is virtually no muscle that cannot be injected on a koi but again there are three main sites with a few less common sites, but in theory there is no end to the possible sites.

This is the main protocol for injections in koi in the United Kingdom. Only very few in the UK do IP injections

The most common site is the in the tail muscle or caudal peduncle

This starts at the base of the caudal/tail fin and moves forward to an area just before the vent region

To pick a point for this type of injection, anaesthetising the koi is preferable.

As the koi lays on its side count four or five scales from the base of the caudal fin along the lateral line, at this point go one scale below the lateral line and slide the needle under a scale (remember only 20% of the full size of the scale is on show) so if you have 5 ml of scale showing you will need to travel another 15 ml under the scale before you can attempt to turn the needle point down into the flesh of the muscle, otherwise you will likely hit a scale and the injection will not penetrate the tissue

Remember to massage the area as the injection substance enters the fish, as this is entering a restrictive muscle area and will expand that area of muscle tissue.

The next popular site is the dorsal area, pick an area level with the leading ray of the dorsal fin and move about 5 ml to one side, as the needle enters under the skin the angle you want again, is to point the needle as though it were too come out through the fishes mouth, this type of injection in this area is prone to blowing back some of the antibiotic because the muscle contracts and pushes the substance back the way it came once the needle is removed, try sealing the entry point with Ora powder as the needle comes out


The ball muscle at the base of the pectoral fin

This is a very popular site as it does not have any scales and has a very high distribution capability, via the pectoral girdle

As the description suggests you insert the needle at the back of the pectoral fin in the ball muscle whilst the koi is anaesthetised

Recommended site, but not for large injections, although it is a very good site for low volume high active ingredient percentage injections

This is also my preferred site for forward fin, Body, mouth or head & face, infections.

In the case of mouth rot I have been known to save a little of the total volume to be injected, about 0.1 ml, and give that right into the upper or lower lip/jaw, to get things moving

Another popular site is under the base of the caudal peduncle again in the tail muscle, this has the distinct advantage of, if an injection related infection sets in as a result of the injection itself, it will not show a scar, much the same can be said of the pectoral ball muscle. Although if you have observed hygiene rules and cleaned the injection site both pre and post injection this should not arise, it does happen on the odd occasion no matter how hygienic you are.

Some examples of IM injection sites

Down side of IM injections are blow back of antibiotic out of the injection site, the risk of infection from the injection site, plus antibiotic distribution is generally not as good as IM


Eliminating air from the syringe

This is a very easy technique and essential

If air find its way into the blood stream an embolism takes place end result dead fish.

After filling the syringe hold up the syringe vertical with the needle pointing upwards pull back on the plunger to create space about 2/3 ml from the top of the syringe this in effect has created an air gap at the top of the syringe, now repeatedly flick the plastic side of the syringe with your finger nail until the air bubbles in suspension in the antibiotic rise and burst on the surface of the fluid. After all evidence of air in suspension has gone, whilst still holding the needle vertical push the plunger up till the fluid rises out of the top of the needle and no more air can be seen, job done.



What ever site you choose, do what you are comfortable with be it IP or IM there is very little to choose between either when comparing the end result I.E. the cure