Parasites (Costia)

Costia is one of the most feared parasites that lives at the expense of our koi. It can reproduce incredibly quickly (through cell division), becoming a true plague that can significantly deplete your stock if adequate action isn't taken.

Description

Costia is a protozoan (also called a protozoan). This is a unicellular animal organism. Costia has two "families," Ichtyobodo necatrix and Ichtyobodo pyriformis. Ichtyobodo necatrix is ​​much more common than Ichtyobodo pyriformis. However, the distinction between the two families is not so important to us, as the external characteristics and control methods are virtually the same. A protozoan can be divided into three categories: Celiates, Flagellates, and Sporoza. Costia falls into the flagellate category. A flagellate is a (usually comma-shaped) protozoan with one or more flagella (whiplike threads) that serve for locomotion and/or attachment and/or feeding. Costia has four flagella, one pair of which is long and one pair short. The long pair is initially used for propulsion and later for attachment, while the short pair is used for feeding.

Features

Costia is an ectoparasite, which parasitizes the koi's exterior. This can affect both the skin and the gills. A characteristic of Costia is that the fish produces excessive mucus as a defense against attack, giving it a somewhat whitish appearance, which is particularly noticeable against a dark substrate. The fish becomes listless and often lies on the pond floor or hangs crookedly in the water ("headstand"). In advanced stages of the infection, frayed fins and wounds can develop. If the gills are severely congested, this is characterized by labored breathing and frequent gulping of air. Sometimes white, calloused patches appear where the skin is severely affected.

Diagnosis

Diagnosis can be made by taking a skin swab. Costia is particularly visible in the area around the mucous membrane, starting at 100x magnification (preferably 200x). It is a very small parasite (15-20 microns) and therefore difficult for the untrained eye to find under a microscope. Therefore, it is often overlooked during microscopic examination of the mucous membrane. Do not use too much mucous membrane for your slide, because Costia is not recognizable against the mucous membrane as a background. Costia is visible in the free areas around the mucous plugs and is characterized by its characteristic locomotion. The parasite rotates on its axis while swimming. Costia is therefore only recognizable in the free-swimming stage; in the attached stage, it blends into the background.

Treatment

First, identify and resolve the primary cause (water quality, stress, etc.). If you don't do this, you're just treating the symptoms and waiting for the next infestation. Formalin is often used for this treatment (sometimes in a so-called FMC mix with other products), but formally, you should only do this on the advice of a veterinarian. Carefully follow their instructions and/or those on the instructions. You are dealing with toxic, harmful substances! A control swab after the treatment can help you determine whether the treatment has been successful.

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