The aim of this study, which was carried out on the main course of River Gurghiu and on some of its tributaries over the year 2009. was to assess the state of the fish communities in the basin of River Gurghiu, and also to highlight significant changes in fish communities. 12 native fish species were found, with an amount of 469 individuals and 4941.5 g. Based on the ecological indices of the fish associations, two fish zones were found in the catchment of the River Gurghiu: brown trout zone and mediterranean barbel zone. Biodiversity in the sampling sites is variable. The highest value of biodiversity index was found on the main course of the River Gurghiu in 2009. The biological integrity index has recorded high values, corresponding with the first integrity class (excellent) in the most of the sampling sites. The overall state of the fish communities in the catchment of River Gurghiu is very well. Consequently, the fish populations have a good self-support capacity.