Parasites: Dactylogyrus (Gill fluke)

Dactylogyrus is a worm-like organism and is therefore multicellular. It is closely related to the previously discussed Gyrodactylus (skin worm) . This worm is about 0.3 millimeters long and, as the name suggests, lives on the gills of fish (ectoparasite), attaching itself with two large hooks and a ring of smaller hooks. The damage this can cause to the gills in the event of a massive infection is considerable. An infected fish often makes scraping movements with its gill covers on a rough or sharp surface. In addition, the fish will try to rid itself of these pests by flushing its gills with a gulp of air (leaving a bubble trail) or sand (if available). In a severe infection, the fish may also keep one gill closed.

Description

The gill fluke (Dactylogyres) should not be confused with the closely related skin fluke (Gyrodactylus). The gill fluke lays eggs, while the skin fluke gives birth to live young (viviparous). For this reason, a different approach is required. The head of the gill fluke absorbs food from the environment and consists of four parts. This immediately reveals the first difference from the skin fluke. In the skin fluke, the head consists of two parts. However, this distinction is difficult to see through a microscope. A much more distinctive difference is that the gill fluke has four clearly visible "eye spots," which allow it to distinguish between light and dark. This gives the gill fluke a somewhat clownish face. These eyespots are absent in the skin fluke. A final essential difference is that the gill fluke lays eggs, while the skin fluke gives birth to live young. If the worm lacks an "embryo" and has four eyespots, you can be sure you are dealing with a gill fluke. Finally, the trained eye will notice the size difference between the skin fluke and the gill fluke. The skin fluke (0.5 mm) is larger than the gill fluke (0.3 mm).

Diagnosis

Diagnosis can be made by taking a skin swab. The worm is a relatively large parasite and can be identified at 40x magnification or higher. It's best to look at it with 100x or 200x magnification to avoid mistaking gill flukes for skin flukes and vice versa.

Treatment

First, identify and resolve the primary cause. Treat with a dewormer in the event of an outbreak and/or visible irritation of the host. Eliminate UV and ozone, and remove absorbents such as activated carbon and zeolite. The eggs are resistant to most pesticides, so multiple treatments are necessary: ​​one to kill the worms and then one (or two) later to kill any larvae that have hatched from the eggs. The rate of egg laying and hatching is closely related to the water temperature. The warmer the water, the faster the entire cycle completes, and therefore the sooner the second treatment should be administered. Perform a check-smear test seven days after the last treatment to see if the problem has been resolved.

Author: Joop van Tol (www.koitoday.nl)