Argulus or fish louse
Argulus or fish louse is a small lobster like animal which lodges on the skin of cypriniformes fish, like koi, but also goldfish. Fish louse can be observed with the naked eye. The fish that have been infected will get red spots. These fish will start behaving differently, like rubbing against stones and jumping above the water.
Fish louse can be treated with special means against diseases including skin worms, gill worms and tape worms. It is wise to put diseased fish in quarantine outside the pond, in order to prevent a plague. It is of course better to prevent fish louse by observing newly introduced fish in order to find out whether they have been infected. In rare cases birds might pass on Argulus to a pond. It is therefore advised to observe fish regularly.
To improve resistance of fish it is important to feed fish during the summer months on good quality feed. Feed, containing a large amount of all important nutrients, vitamins and minerals. Healthy fish can resist attacks of fish louse more easily.