GILL AND SKIN FLUKES OF FISH
21-04-99
By Jim E. Quarles.

Believe it or not gill and skin flukes are common flatworm parasites of fishes. When adult, the worms are translucent pink to white with a yellow yoke.

Are they a problem: Yes in aquariums they can become 'Epidemic', resulting in massive fish kills. A very large percentage of sick and dying fish can be traced back to these parasites.

Fill flukes graze on gill filament blood, slime and epithelial tissue and when present in large numbers can cause severe irritation.

In the wild, a species of gill fluke may live on only one kind of host fish or on several with like life histories. A single kind of fish may be host to several kinds of gill flukes.

The known number of species is about 1900 types and this is far from the total in nature, since the study of parasites is on going and still in its early stages so to speak.

The head end of gill fluke has a mouth and four light sensitive eyespots. At the rear end is an attachment organ, called the opisthaptor. The structure of this opisthaptor divides the flukes into two groups.

The study of the two groups is beyond my intent in this article, but is a interesting subject in and of its self. However, it needs to be understood that these two groups use different methods to attach themselves to the host fish. Some have a single attachment, these intimidating anchors don't burrow into the fish but rotate to raise up the haptor and create suction to help hold the suction disc in place. A second group comes with multiple attachment structures called clamps.

There are lots of flukes that live on the skin and not the gills of fish and these are always of the mono or first group. There are some that live in the urinary bladder of tree frogs.

Reproduction: Hermaphroditic, gill flukes transfer sperm to each other and produce fertilized eggs all their adult lives. The eggs of some species sink to the bottom, and in other species are embellished with entangling filaments that give them lift in the water column and also can wrap around the fishes gill arches. Within one to four weeks the egg hatches into tiny ciliated larva. Under the microscope it looks like a ciliated protozoan with tiny hooks. It swims around until it dies or finds a suitable host fish, most of them settle down, loses it cilia and becomes a miniature or juvenile worm that grows and feeds on the gills of the new fish, and when it is fully adult it will search for another of it's kind with which to mate.

So what are the odds of any one dislodged egg entangling in the gill of the right kind of host fish before hatching? That depends on what kind of fish the host fish is and how crowded they are in a given collection off eggs. In the home or hatchery tropical fish tank the odd are pretty good the egg will find a host fish.

By keeping fish in captivity, you increase the odds of a epidemic out break of gill and or skin flukes. This produces extensive gill irritation, erosion, and heavy bleeding from the gills and even provide cuts and sores for opportunistic bacteria and fungi to invade the bloodstream.

When this occurs you have overwhelming systemic infections. It is a condition found frequently in hatcheries and sometimes in home aquaria, especially in tanks densely stocked with one species of fish, ( breeding tanks ).

Fortunately, we have several treatments for gill flukes, but not all treatments are effective on different kinds of fluke, and you might have to try several before eliminating an outbreak. I will cover some of those treatments in part 4 of this article.

But every hobbyist should be aware of damage by gill flukes and keep on hand different medications recommended for their control. Most often by the time you are aware of the danger, and rush out looking for the proper medications, you are to late to head off the outbreak in a timely manner.

In part 3 of this article I will cover Roundworms (Nematodes.) Which include the tapeworm which is commonly a problem in captive fish.