Mariculture is a branch of aquaculture that deals with the cultivation of marine organisms. Croatia, considering the relief and resources, has very good opportunities for the growth and development of mariculture. Given that the demand for fish is increasing, and the amount of fish in the wild is decreasing, the production of sea bream (Sparus aurata) and other species is increasing, there is an expansion of farms and a larger number of cages, but in parallel there is also an increase in the number of pests and the spread of pest diseases. Sparicotyle chrysophrii (Van Beneden and Hesse, 1863), a gill pest that has a direct life cycle, is the most dangerous pest for the culture of cultivated sea bream (S. aurata), which is often found in mixed infections with other pests and secondary bacterial infections, so many times responsible for large losses in production. The goal of this thesis was to determine the number of diseased sea breams, that is, the amount of parasites on the gills of the fish, and in relation to the temperature, it must follow the severity of the infection of S. chrysophrii. The research was carried out on the Cromaris farm, which is located on the island of Ugljan, more precisely, right next to the bay of Lamjana, in the period from March 2017 to May 2018. For the purposes of this research, 100 individuals were taken randomly from four production cages during the mentioned research period. Biometric measurements include weight, length and fish condition index. Parasitological examinations of the gills were performed using a microscope, and the hematocrit value was read using hematocrit tubes and a centrifuge. The average abundance and prevalence of pests was recorded. Given that the research began with the planting of fish in March, with an average weight of 6.80 grams, the increase in temperature in the following months affected the faster growth and development of the observed fish, so already in August the fish reached a weight of over 100 grams. The increase in the average abundance and appearance of the pest was greater during the warm months, especially in August when the abundance was over 4. The increased average abundance during the summer months did not have a great impact on the health condition of the underlings, and the drop in the hematocrit value was caused to a lesser extent by the infection of the intruder, while the main part was due to the drop in temperature during the winter period.