Department of Parasitology, Faculty of Veterinary Medicine, Islamic Azad University, Science and Research Branch, Tehran, Iran

Ligula intestinalis worm is the cause of ligolosis. It is the most common parasitic infection of freshwater fish in most parts of the world and causes many economic losses including weight loss, fertility decline and mortality in baby fish. Therefore, taking measures to diagnose and control it become very important, in breeding pools and fish farms management. The adult Ligula intestinalis worm can be found in the small intestine of the angry birds and the larva stage of the worm (plerocercoid) in the abdominal cavity of fish. The aim of this study was to detect Ligula intestinalis parasitic infection in river whitefish in Alborz dam, Mazandaran Province. To this end, in September 2016, 60 fish of the species were captured randomly and referred to the laboratory for morphometric and parasitic examination. The results showed that all fish caught were infected. Since Ligula intestinalis plerocercoid can reduce or not fertilize young fish, it is essential. to consider strategies to combat this parasite.