Anchor Worm/Lernaea
This crustacean parasite, a relative of the crab and lobster, is more commonly known to the Koi keeper as Anchor Worm. It is obviously named because of its body shape, but this can be very misleading as usually half of its body is embedded in the flesh of the fish, the anchor shape is not immediately obvious. There is a small bonus to the shape of this parasite, having removed an Anchor Worm with tweezers, you need to look closely at the parasite, if it is not anchor shaped then you have left half of the parasite in the flesh of the fish. You need to have another look at the wound and remove the other half; it is essential that the other half be removed. Having completed the total removal, dab the wound with a bactericide suitable for topical application; some bactericides are for pond use only.
It is advisable to check the whole body of the fish on which you have found Anchor Worm. They are masters of disguise and frequently attach themselves near the fins, but will equally burrow under the scales anywhere on the body, leaving only the rear end of the body exposed. This itself resembles a a very thin fish bone, and this is sometimes what the Koi keeper assumes they are observing, a small protruding piece of bone. When the Anchor Worm is located near a fin, the observer could easily mistake the parasite for one of the rays of the fin that has lost its fine membrane.
Anchor Worm has a very complex life cycle compared to other parasites. During its life this parasite is continuously changing its form in order to perform new functions as it matures, this process is called metamorphosis. Its is only the female that is parasitic to Koi, the only objective of the male is to fertilise the female, once that has been achieved it dies. The fertilised female burrows into the flesh of the host fish in order to lay her eggs safely. She continues to metamorphose, and develops the anchors after she is embedded in the fish. The ovaries then move position down the body, just before she is about to produce her eggs, the yellow egg sacs can clearly be seen on the reproducing female. It is inside these paired egg sacs, that the eggs themselves mature. The sacs are shed and the new generation of Anchor worm actually break out of the egg sacs.
At this early stage, the young Anchor Worm are known as naupilii, and are oval. Water temperature has a great deal of influence on their development, but around 50 hours after birth, they moult to become metanaupilii. Then begins a series of stages in which the organism is termed a copepodid, and each development stage has a number. They reach sexual maturity at the sixth copepodid stage, and that is when fertilisation of the female takes place, and she seeks a host fish.
It is only the final stages of the complex life cycle of this parasite that can be seen with the naked eye, all other stages are not visible to the eye.
Larger fish cope better with Anchor Worm until the numbers parasitising the fish are very high, and then the fish will become debilitated. It is also possible that bacteria and other diseases could enter the body through the wound created by the parasite. Fry and smaller Koi are far more vulnerable to Anchor Worm, as there is fat less body area they are likely to succumb to high numbers.
In Japan Anchor Worm is not in itself ever regarded as a serious parasite, it is the possible secondary problems that are the main risk. The only time pond treatment is required is when the parasite is seen to be breeding out of control.
Whilst this parasite can cause a marked behavioural reaction in some fish species, in Koi the Anchor Worm seldom cause any change to their normal behaviour pattern. Neither does it affect the appetite of the affected Koi, in the way other parasites can do. Although if any Koi become very heavily infested by any parasite it is not likely to want to feed, particularly if secondary complications were developing.
There may be some localised irritation to the body of the Koi that give rise to slight flicking, but in most Koi there is no reaction to a few Lernea. It will take a substantial attack to upset Koi, larger fish cope very well, obvious smaller Koi are more threatened.
Constant improvements in medication are made to eradicate this parasite, please contact us for treatments and correct use of dosage for your pond and Koi.
It is advisable to check the whole body of the fish on which you have found Anchor Worm. They are masters of disguise and frequently attach themselves near the fins, but will equally burrow under the scales anywhere on the body, leaving only the rear end of the body exposed. This itself resembles a a very thin fish bone, and this is sometimes what the Koi keeper assumes they are observing, a small protruding piece of bone. When the Anchor Worm is located near a fin, the observer could easily mistake the parasite for one of the rays of the fin that has lost its fine membrane.
Anchor Worm has a very complex life cycle compared to other parasites. During its life this parasite is continuously changing its form in order to perform new functions as it matures, this process is called metamorphosis. Its is only the female that is parasitic to Koi, the only objective of the male is to fertilise the female, once that has been achieved it dies. The fertilised female burrows into the flesh of the host fish in order to lay her eggs safely. She continues to metamorphose, and develops the anchors after she is embedded in the fish. The ovaries then move position down the body, just before she is about to produce her eggs, the yellow egg sacs can clearly be seen on the reproducing female. It is inside these paired egg sacs, that the eggs themselves mature. The sacs are shed and the new generation of Anchor worm actually break out of the egg sacs.
At this early stage, the young Anchor Worm are known as naupilii, and are oval. Water temperature has a great deal of influence on their development, but around 50 hours after birth, they moult to become metanaupilii. Then begins a series of stages in which the organism is termed a copepodid, and each development stage has a number. They reach sexual maturity at the sixth copepodid stage, and that is when fertilisation of the female takes place, and she seeks a host fish.
It is only the final stages of the complex life cycle of this parasite that can be seen with the naked eye, all other stages are not visible to the eye.
Larger fish cope better with Anchor Worm until the numbers parasitising the fish are very high, and then the fish will become debilitated. It is also possible that bacteria and other diseases could enter the body through the wound created by the parasite. Fry and smaller Koi are far more vulnerable to Anchor Worm, as there is fat less body area they are likely to succumb to high numbers.
In Japan Anchor Worm is not in itself ever regarded as a serious parasite, it is the possible secondary problems that are the main risk. The only time pond treatment is required is when the parasite is seen to be breeding out of control.
Whilst this parasite can cause a marked behavioural reaction in some fish species, in Koi the Anchor Worm seldom cause any change to their normal behaviour pattern. Neither does it affect the appetite of the affected Koi, in the way other parasites can do. Although if any Koi become very heavily infested by any parasite it is not likely to want to feed, particularly if secondary complications were developing.
There may be some localised irritation to the body of the Koi that give rise to slight flicking, but in most Koi there is no reaction to a few Lernea. It will take a substantial attack to upset Koi, larger fish cope very well, obvious smaller Koi are more threatened.
Constant improvements in medication are made to eradicate this parasite, please contact us for treatments and correct use of dosage for your pond and Koi.