Correlation between water quality and prevalence on Koi (Cyprinus carpio) which infested by Argulus in Mungkid Subdistrict and Muntilan Subdistrict, Magelang Regency, Central Java

Koi (Cyprinus carpio) has an interesting added value which one of the most famous freshwater ornamental fish. There are a lot of factors which have to be faced when we were trying to cultivate or culture Koi; one of those factors is the disease. Ectoparasite is one factor that can be the decline on koi selling because the ectoparasite can reduce the selling point caused by the effect on koi. One of ectoparasite known as attack koi is Argulus. The purpose of this research to determine relations between water quality and the prevalence of Argulus on Koi (Cyprinus carpio). The research was conducted at Magelang, Central Java (on Mungkid's and Muntilan's region). Measurement of water quality was temperature, pH, DO, and ammonia. This research use survey method and take the sample with random sampling. The result of this research shown that the prevalence of Koi that infested by Argulus in Mungkid subdistrict are 30.77 %, and in the Muntilan sub-district are 55.17%. There was a positive correlation between water quality and the prevalence of Argulus especially at the temperature, which has a significant correlation. Higher temperatures will also increase the Argulus prevalence.