Fish Leech Piscicola geomtra fish parasite

This is the most common fish leech that is found in garden ponds. Whilst being a parasite it differs from Anchor Worm (Lernea) and Fish Louse (Argulus) as it only attaches to the host fish to feed, dropping off afterwards and hiding at the bottom of the pond in order to digest it's meal.
It can survive for long periods without feeding. Piscicola geometra is often introduced to ponds on plants.

Being clearly visible without magnification, it measures up to 25mm in length and appear to be pale brown, or brown and white striped, in colour.  Piscicola geometra is a strong swimmer and can move rapidly across the pond searching for it's next host.
The leech can attach to any part of the fish with it's sucking disc, it then pierces the skin with it's specialised mouth parts and will stay attached, sucking blood, until satiated. The wounds caused by this action may develop secondary bacterial infections or fungus. Piscicola geometra is also known to be a factor in the spread of viral diseases such as (Spring Viremia of Carp) SVC.

Life Cycle

Piscicola geometra reproduce after several meals, they are oviparous (producing eggs that hatch outside the body), laying their eggs in dark brown oval cocoons which are attached to the debris on the bottom of the pond, plants, planting baskets, etc.

The life cycle of Piscicola geometra takes up to 30 days. The life cycle of other species may take anything from 24 days to several months depending on water temperature and availability of hosts.

Symptoms

flashing
rubbing against side or bottom of pond
lethargic
stop feeding
sitting on the bottom with their fins clamped
skin may have a milky appearance due to an increase in mucus secretion

Due to their size attached fish leeches can be easily seen without magnification.

Treatment

The most effective chemical treatments against fish leeches were organophosphates, Dimilin, Masoten and Malathion, but they are now banned in the UK for use in fish treatments.

Attached leeches may be carefully removed with tweezers, the fish may need to be anaesthetised for this. After removal the wound needs be treated with antiseptic spray or gel to reduce the risk of secondary bacterial infections or fungus.
Alternatively, Malachite Green can be applied topically with a cotton bud.
Unless you eradicate leeches the fish will become reinfected on return to the pond.

The only way to eradicate leeches is:

Remove the fish from the pond to an aerated holding/quarantine tank. be sure to check each fish over and remove any leeches. Salt may be added to aid recovery and reduce the risk of secondary infections.

The pond should then be left empty of fish for about one month to break the life cycle. Newly hatched leeches will soon die with no hosts to feed on. Alternatively, drain the pond and leave it dry for about a week. Dehydration will destroy the eggs as well as the adult leeches.
This of course will depend on the size of your pond, it is fairly easy to do with a small pond but obviously not     practical for a larger pond or lake.