Dactylogyrus

Also known as: Gill Fluke

Introduction

The parasites of the Dactylogyrus species are monogenean trematodes of the family Dactylogyridae.

Members of the Dactylogyrus species prefer to live on the gills of host fish, most often cultured Cyprinids (common carp, grass carp, silver carp). The adults are oviparous and the eggs are released into the water to hatch. These eggs are often very resistant and can survive chemical treatment. The emerging ciliated larvae are carried to a new host by water currents and by their own movement.

The maturation time of Dactylogyrus species from egg to adult depends on the temperature. At approximately 20°C it only takes a few days, but at approximately 2°C it can take several months.

The adult fluke attaches itself to its host by the opishaptor which hooks into the surface of the skin. The flukes live on mucus and skin debris and in small numbers do not seem to cause any harm.

In moderate numbers, the flukes can lead to severe destruction of the gills resulting in haemorrhage and metaplasia of gill tissue. Secondary bacterial infections can occur and result in death of the fish.

Clinical Signs

Grossly, the gills appear swollen, with excessive mucus secretion and increased opercular movements.

The fish may be lethargic and anorexic and swim on the surface of the water.

Diagnosis

Diagnosis is based on the identification of the fluke during examination of the gills. The gills can be completely removed or gill clippings can be taken from the infected fish to prepare a diagnostic sample. The parasite can then be removed from the gill and placed on a slide under a coverslip.

Dactylogyrus species have 4 eye-spots, 14 marginal hooks, two anchors, one to two connective bars and two needle-like structures and spindle-shaped dacrylogyrid-type seminal vesicles.

Treatment and Control

Chemicals are the main method of treatment and control.

Chemical treatments via dips or baths in salt, formaldehyde or organophosphates are all possible.

Potassium permanganate is also effective and is the treatment of choice if bacteria or fungi are invading the damaged tissue.

Repeated chemical treatments may be necessary as the eggs are very resistant. Cleaning of tanks may help eliminate the eggs.

Prevention relies on effective quarantine measures to prevent the introduction of the fluke to a group of fish.

Dactylogyrus Learning Resources
Flashcards Test your knowledge using flashcard type questions	Ornamental Fish Q&A 25

References

Woo, P. (2002) Diseases and disorders of finfish in cage culture CABI

Reed, P. (2009) Monogenean Parasites of Fish University of Florida Publishing