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The aims of this study were to determine the influence of the factors affecting fin damage under different rainbow trout production systems and to compare the findings with the known experimental reports. The study was based on a questionnaire that included information about the main factors i.e. oxygen level in exit water, water temperature, stocking density, daily feed ration, number of meals and grading frequency on seven rainbow trout farms. Standard multiple regression analysis, based on a previously published fin damage dataset, was used to assess the relationship between the level of fin damage per fin and the factors. Daily feed ration received the strongest weight in the model for the caudal, anal and both pectoral fins, whereas number of meals received the strongest weight in the model for both pelvic fins. Grading frequency received the strongest weight only in the dorsal fin model. Lower levels of daily feed ration and number of meals combined with higher water temperature increased the level of fin damage, whereas stocking density had no effect. The results conform to the experimental research on fin damage in rainbow trout. The research model contributes to the overall assessment of fish welfare and the regression analysis used in this study could be used on rainbow trout farms to evaluate the effect of the main factors on the level of fin damage.

Trichodinids are probably the most commonly encountered protozoan parasites on fishes in marine and freshwater environments. They are typically found on the gills, skin and fins of fish. The aim of this study was to evaluate the prevalence and mean intensity of Trichodina sp. in freshwater fish from cyprinid aquaculture facilities in Macedonia. This study was carried out by seasons, in a period of three years. A total of 578 specimens of common carp (Cyprinus carpio, Linnaeus 1758), 76 specimens of grass carp (Ctenopharyngodon idella, Valenciennes 1844), 47 specimens of silver carp (Hypophthalmichthys molitrix, Valenciennes, 1844) and 53 specimens of bighead carp (Hypophthalmichthys nobilis, Richardson, 1845) from the most significant and larger cyprinid aquaculture facilities in Macedonia, including fish farms and reservoirs, were examined for parasitological investigations. Infestation with Trichodina sp. was found in 206 specimens of common carp in all aquaculture facilities examined, in all seasons, as well as, in 9 specimens of grass carp from two fish farms, only in autumn season. Total, the prevalence with Trichodina sp. was 11.84% (grass carp) and 35.67% (common carp), while the, mean intensity was 7.56 (grass carp) and 4.56 (common carp). The prevalence with Trichodina sp. in common carp by season was as following: spring-11.82%, summer-3.44%, autumn-7.85%, winter-7.05%, while the mean intensity was: spring-4.55; summer-4.67; autumn-4.40; winter-4.72. Our findings of Trichodina sp. in grass carp in the present study is considered as the first record in Macedonia. Also, this fish species is regarded as new host for Trichodina sp. in Macedonian waters. Pasożyty zewnętrzne ryb słodkowodnych Macedonii z rodziny Trichodina (Ciliophora: Peritrichida) Słowa kluczowe pierwotniaki, Trichodina sp., amur biały, karp, akwakultura Streszczenie Trichodinidae są prawdopodobnie najczęściej spotykanymi pierwotniakami pasożytującymi na rybach słodkowodnych i morskich. Zazwyczaj spotykane są na skrzelach, skórze i płetwach ryb. Celem artykułu jest określenie częstotliwości i intensywności zarażenia ryb karpiowatych przez Trichodina sp. Badania trwały trzy lata. Łącznie przebadano pod kątem parazytologicznym 578 osobników karpia (Cyprinus carpio, Linnaeus 1758), 76 amurów białych

A total of 958 specimens of common carp from the most significant and larger cyprinid aquaculture facilities in Macedonia, including fish farms and reservoirs, were examined for parasitological investigations. Eudiplozoon nipponicum was found on gills in 121 specimens of common carp in spring, summer and autumn, with a prevalence of 10.67 %, and a mean intensity of 2.55. Our findings of E. nipponicum in common carp from aquaculture are first recorded in Macedonia.

Large freshwater mussels (Unionida) are long-lived, have large bodies, and produce thousands to millions of larvae (glochidia) that usually must attach to host fish tissue to complete their life cycle. This is an obligate parasitic stage of mussel larvae. However, less than one in onemillion find a suitable host and survive. The degree of host specificity varies among unionid species, from specialists that can successfully parasitize only one or a few closely related fish species to generalists that can complete development on a taxonomically broad range of fish species. In addition, freshwater mussels are among the most threatened groups of animals. This is due to habitat destruction, the introduction of non-native species, and the loss of host fish on which their larvae (glochidia) are obligate parasites. Glochidiosis harms fish by affecting their growth; on the other hand, freshwater mussels play an important role in freshwaters by improving water quality and ridding the water of bacteria, algae, and pollutants, they are an indicator species of water quality. During our parasitological survey of fish from the Macedonian part of Lake Prespa in April 2022, many glochidia were found on the gills, skin, and fins of two endemic fishes, Prespa roach (Rutilus prespensis) and Prespa nase (Chondrostoma prespense), in the range of tens to thousands on one host. We thus recorded these two endemic species as new hosts of A. cygnea.